Fraser Cain:  Ninety-nine episodes Pamela!

Dr. Pamela Gay: I know [Laughter] it’s amazing how far and how long we’ve been doing this.  

Fraser:  The Milky Way is our home galaxy but we’ve only understood its true nature for about a century.  We share this beautiful barred spiral galaxy with at least 200 billion other stars.   

Let’s trace back the history, see how we learned about the Milky Way and then compare it to other galaxies out there.  What does the future hold for the Milky Way?

Pamela: The future holds death, because that’s kinda what happens in the Universe. [Laughter]

Fraser:  Shhh….we’re supposed to keep that as a surprise!  It all ends in tears.  But, let’s go back to the beginning.  [Laughter] I find that kinda interesting.  My dad had an antique book about Astronomy.  It had all the constellations and stuff.  It was back from like the 1920s or earlier.  It had nebula for the Andromeda nebula and other stuff. 

Let’s go back like as far as we can and talk a bit about the history of the Milky Way.  You could see the Milky Way in the night sky so people knew that there was something there.  What did they think was going on?

Pamela: Well the term Milky Way is actually derived from a Latin term.  We’ve had that name for it for a long time.  It basically comes from the fact that there is this band of light that to the naked eye is perceived as this light patch, this illuminated patch that spreads in an arc across the sky.  

If you’ve ever gone somewhere truly truly dark, someplace where the nearest light is miles away and there are no cities for hundreds of miles, in these truly dark locations when you look up and there’s a cloud, the cloud is the blackest thing in the sky.  When you see a band of light, it is just like what is that?  That’s not supposed to be there.  

The Milky Way is that unusual band that crops up in the sky in dark locations and startles you.  In our modern light polluted world, we’re used to the clouds being the bright things in the sky.  To someone living in a world illuminated by fire it was the Milky Way and it literally looked like someone had spilled milk across the sky and that’s where the name came from.  

It wasn’t until we had telescopes that it was possible to look up at this band of what appeared to be continuous light and see that it was nothing more than thousands and thousands of stars all packed closely together.

Fraser:  That was sorta the first major discovery.  I thought it was Galileo when he turned his telescope on the Milky Way about 1610 I think and that’s what he saw was just stars everywhere he looked.

Pamela: It sounds almost like an episode of 2001 – stars it’s all stars.  In looking at this band of stars what’s neat is we see structures.  We see dark striations through it.  We see that it expands out and gets brighter when we look toward the Constellation Sagittarius.  

As you travel around the globe you can see it from both hemispheres.  It’s something that we share.  It comes up higher in the north and lower in the south so there is this ring of light that essentially goes all the way around our Solar System at this crazy angle and it is symmetricish so that we see the same amount in the north and south.  

All of this says that we’re basically embedded inside of a disk that’s tilted relative to the Solar System and that we must be located pretty much in the center of that disk.  If we weren’t in the center of the disk then we’d see more of it to the north and more of it to the south.  

When I say that we’re in the center of the disk it sounds like you sorta stick your head in the center of a hoola-hoop and because you’re head is in the center of the hoola-hoop, everything is orbiting around you.  

Another way to perceive this is what if you’re inside of a disk that’s really big and you can only see a small section of it?  That small section might appear to be a perfect circle that you’re embedded in the center of.  People originally thought hey, we’re in the very center of – well not the Solar System – but at least in the center of the Galaxy.  It turns out that’s not the case.

Fraser:  Right, I know that William Herschel took a shot at trying to map out the shape of the Milky Way.  He counted stars in all the directions and drew a diagram and he thought that the Solar System was sorta in the center of the Milky Way.  Herschel discovered Uranus, right? 

Pamela: Right, yeah.

Fraser:  He was one of the most famous Astronomers at the time so he took a good shot at it.

Pamela: In looking at the stars and counting the stars around us, you end up with equal numbers of stars more or less in all directions.  Now the problem is there is also dust.  So we can’t see all the way out to the edges of the Milky Way using normal colors of light that our eyes can see, at least not when we look out through the disk.  

If instead you look above or below the disk you can see these blobs of stars called Globular Clusters.  If you start mapping the distance to the Globular Clusters, you start realizing that they aren’t symmetric.  There are more of them when you look above and below the Constellation Sagittarius. 

There are fewer of them when you look in the opposite direction and as you start to plot them it looks like in reality we’re roughly a third of the way out from the center of a spheroid that is marked by these Globular Clusters.  

Fraser:  I see, so it’s like you can see all of the Globular Clusters that are just above the center of the Galaxy.  You can see the ones that are embedded in the disk with us, but all of the ones that are obscured by the dust on the other half of the Galaxy you just can’t see them.

Pamela: Right.  In plotting those that are above and below and trying to get at this three dimensional structure we realized the Globular Clusters form a halo of objects, a sphere of objects and we’re not in the center of that particular sphere. 

So, let’s step back and figure out why is it that when we count stars, that doesn’t work.  The reason it doesn’t work is that there is so much gas and dust blocking light that we can only see a little way out into the Milky Way’s disk when we use visible light.  

One of the neat things about light is different colors act in different ways.  While the blue light that might come off of a party light bulb won’t pass through the walls of my house, a wireless internet passes quite happily through house walls.  Wireless internet is just a beam of light that is coming away from the little wireless router sitting in my kitchen and passing through floors and ceilings and walls and everything else I have in my house.  That color goes through stuff.  Wireless internet is really just a red shade.  It’s off in the microwave radio part of the color continuum.  Often that part of the electromagnetic spectrum.  Now as you get redder and redder in general, light is able to go through things more easily.  

So, if you try and shine blue light through a cloudy fish tank, you’re not going to get a lot of that light through to the other side. But if you try and shine red light through a cloudy fish tank, you’ll get more of the light passing through.  What is really cool is if you take a 2-liter bottle and put a little dried milk in it and shake it up with water and shine white light through it you’ll see the blue light scatters left and right and the red light goes straight through.  

Those little particles of dried milk in that 2-liter water you mixed up act the exact same way that dust in our Galaxy works.  So blue light from stars in the center of the Galaxy gets scattered in all directions – it doesn’t make it to us.  But red light from stars in the center of the Galaxy can pass right through that gas and dust and get to observers.  

You just need build the instruments to look at the center of the Galaxy, the infrared and the radio.  By going to these longer wavelengths we’ve been actually able to see stars orbiting the central Super-Massive Black Hole in the middle of the Milky Way.  We’ve been able to see that there are a lot more stars when you look toward the center of the Milky Way than when you look away towards the outer part of the Galaxy.  

Fraser:  So what finally clinched the argument?  What finally told people that we live in an island of stars and that those other things aren’t nebulae but actually other Galaxies?

Pamela: That was actually the first time that we were able to see variable stars in another Galaxy.  When we looked out at the Andromeda Galaxy with a big enough telescope and were able to make out Cepheids there and work out the distance, that was the key.  There are these very bright stars called Cepheids that vary in such a way that their period is directly related to how much light they give off.  It is directly related to their luminosity.  

When you look at one of these stars, you measure how long it takes to go from being really bright to being faint and being bright again.  Then you look at a chart and you can figure out how far away that object is.  We’d figured this out for the large and small Magellanic Clouds.  

Globular Clusters don’t tend to have those particular types of stars.  We knew that pretty much all the stars in the large and small Magellanic Clouds are affectively going to be the same distance, the same way everyone in Beijing is the same distance from me even though there are slight variations depending on if they are on the near side or the far side of the city.  The distance between here and Beijing is just that much bigger than the size of Beijing.  

Using the relationships that we worked out using the Magellanic Clouds, Astronomers then went and looked at the Cepheids in the Andromeda Galaxy and basically had a moment of, “oh dear, I need to sit down now,”  and realize just how much further away the Andromeda Island of Stars, the Andromeda Galaxy is away from the Milky Way.  They realized that’s an entirely different type of object.  

So, all of a sudden we were the Milky Way Galaxy, the Andromeda Galaxy and we started to sort out that these other spiral shaped and elliptical shaped, smudges in the sky in some cases were Island Universes – Galaxies all in their own right.  

It took us awhile to sort out which object is a Globular Cluster, which object is a Planetary Nebula and this object is….we had to go through and build bigger telescopes to be able to make some of the final decisions on what the different smears of light were on the sky.  We made it and we have an entirely new understanding of the Universe.

Fraser:  With our current modern understanding of the Milky Way, let’s talk about some of its dimensions.  How big is it?  

Pamela: [Laughter] This is actually one of those things that is kinda fun to look up because the numbers are all over the map.

Fraser:  Oh, this is one of those textbook out of date questions, isn’t it?

Pamela: Right, right.  The problem is we can’t see the whole thing.  We’re sorta inside of it and even if we weren’t inside of it there are problems with looking in all the right colors to catch all the parts of the Galaxy.  

It is only by mapping things in detail using infrared that we’re able to finally make out the full extent of just the luminous matter in galaxies.  There was a big science article a year or so ago where all of a sudden the Andromeda Galaxy pretty much doubled in size because we were able to find more stuff than we knew about when we started looking in infrared.  

The canonical number that you see pretty much everywhere is the Milky Way Galaxy is 100,000 light years in diameter.  You’ll find numbers that go up to 120,000 light years when people start including tidal streams.  

I suspect that number may still go up even further as we identify a shredded object in one location that clearly been completely destroyed and these stars now belong the Milky Way are just going to be claimed as our suburbs.  

Fraser:  Right.  It’s almost like you have to calculate what is the theoretical limit of the force of gravity from the Milky Way?  That would give you a certain number and you won’t be surprised if you keep turning up objects that fit within that.

Pamela: And it is also a matter of where are the edges of the gas and dust that has been stripped out of things?  Where are the edges even to the Dark Matter Halo?  That’s really going to be the final answer of once something is embedded in that Halo it’s ours.  We own it?

Fraser:  How big is the Halo?

Pamela: This is something that we’re still sorting out.  There are all sorts of different models that lead to different sized halos.  So, as we get better at mapping Dark Matter hopefully someday in the future I’ll be able to answer that question for you.  Right now I’m going to stick to as far as we know the luminous part of the Milky Way is about 120,000 light years in diameter.  

Fraser:  Okay, we know the size, so what about the stars?  How many stars?  

Pamela: Well that’s still up for debate.  It’s hard to find the little ones.  Current estimates are somewhere between 200 billion and 400 billion.  Which is a lot and it is just kinda cool that the number of stars is basically 100 times the number of people we have on the planet Earth.

Fraser:  Isn’t it like kind of the same number as the number of galaxies there are in the Universe or something like that?

Pamela: Well that presumes we actually know how big the Universe is.

Fraser:  Right, right.  We’ve done a whole show about that.

Pamela: Right we have no clue. [Laughter]

Fraser:  Okay, are there any other interesting dimensions to the Universe then?  How far away are we from the center?  

Pamela: It looks like we’re about 27,000 light years from the center.  The other number that is kind of interesting is if you try and look at the thickness of the disk – how much above and below – us there is of gas and dust and stars that makes up this disk.  Most websites you find will say it is about 1,000 light years thick.  

But there is a group down in Australia led by Brian Gansler, an absolutely wonderful fellow who puts out more brilliant press releases than any other one person I can easily identify.  His team decided to go through and work out those calculations.  

When they worked the calculations they discovered that the number that everybody quotes is wrong.  It turns out that the disk of the Galaxy is actually about 6,000 light years thick.  It suddenly got six times bigger when someone bothered to redo the numbers.  The way we get it is that we look at how light from Pulsars travel through the disk of the Galaxy.  The light actually gets changed when it hits the gas and dust in the disk.  

So if you look at a bunch of Pulsars that have known distances, and you measure how their light travels to us, the amount that it is distorted by the Milky Way gives us an estimate of how thick the Milky Way is toward that star.  

You do this for a bunch of stars and you eventually figure out what is the thickness of the disk.  They increased the number by six by just doing the calculation a new time.  That’s kinda cool

Fraser:  What kind of Galaxy are we?  I know we’re a spiral but more specifically.  

Pamela: We’re actually a Barred Spiral and this is fairly new knowledge.  There has been a lot of work between Spitzer and the Sloan Digital Sky Survey and all these new great technologies that have only been around since about 2000.  They have been systematically going through and plotting anything out there to be plotted in a 3-dimensional map of the Galaxy.  

They found that on the inner part of our Galaxy is a bar that is about 20,000 light years in length.  The center of the bar marks the center of the Galaxy.  This bar is a completely new discovery.  It has only been known really well since 2005 and this makes us a Barred Spiral Galaxy.

Fraser:  Right and I think I’ve seen this.  You take the center Halo of the Milky Way and you extend out two directions with a bar and then at the ends of the bar, you make right hand turns in both directions then you spiral out the spiral arms from there, right?

Pamela: Right.  Exactly.

Fraser:  So does that give us two spiral arms?  

Pamela: We have two spiral arms but we didn’t even know that until this year (2008).  It was thought that well there were two spiral arms but we also thought we saw these two other spiral arms so somehow we had one bar and four arms and no one knew where anything was connected.  This is kinda weird and doesn’t generally happen in the things that we see when we look out in the Sky.  

But it turns out that a couple of the bars were just places where we thought we saw more stars.  When you take the time to observe in infrared and look through the dust and gas and see what’s actually there, you see there are really only two arms.  That was a kind of cool discovery.  

Then if you can imagine flying out of the Milky Way and looking down on it from a great distance, it appears there is actually an outer ring of stars as well from something we decided to consume and just store as the ring.

Fraser:  The arms have names.  Which arms are there and which arm do we live in?

Pamela: Once upon a time when our Galaxy, which I think both of us have now called the Universe at least once in this show, we know it’s a Galaxy but it slips.  Once upon a time the Milky Way Galaxy had four arms.  

We called them normones which I just find the funniest name ever for a galactic arm: the Scutum- Centorus arm, Sagittarius and Perseus arm. We live in the ‘A’ spur called the Orion Spur.  It turns out my favorite named arm Norma isn’t actually there and neither is the hard to pronounce Scutum-Centorus Arm.  Now we’re left with just the Sagittarius and Perseus arms of the Milky Way.

Fraser:  There you go.  We live in the Orion Spur which comes off which arm?

Pamela: The Orion Spur appears to be part of the Perseus Arm.  It is still complicated trying to map out everything from the inside.  But we’re making progress so if you truly wanted to give the planet Earth an address, it would be:  Planet Earth, in the Solar System in the Orion Spur of the Perseus Arm of the disk of the Milky Way Galaxy.  

Fraser:  Of the local group of the Virgo Super Cluster of the Universe.

Pamela: I’m sure that there is some sort of large-scale structure junction that we can say that we belong to.

Fraser:  Right.  I was such a Geek as a kid; I did that as my return address on letters that I would send out. [Laughter] I did Earth, Solar System, Milky Way, Local Group, Virgo Super Cluster, Universe.  Yeah, I did that.

Pamela: I had a friend that I met at Space Camp and he and I would do that as well.  And in retrospect now what amazes me is the U.S. Post Office.  If you have kids’ handwriting the Post Office will actually deliver letters that have that level of obnoxious addressing on it.

Fraser:  Well if they will deliver to Santa Claus, you know….. [Laughter]

Pamela: That’s true.

Fraser:  So I think we have the characteristics, now how old is the Milky Way and how do we know?  

Pamela: That’s one of those questions that we can’t really answer because what do you use to measure that?  If we look out at the older stars – yeah we’ve got old stars.  Some of the oldest stars we are part of the Milky Way.  We don’t know if those stars formed before the Galaxy, with the Galaxy or after the Galaxy. 

We really can’t say how old the Milky Way is.  But what we can say is it is going to cease being the Milky Way in somewhere between five and seven billion years from now when it merges with the Andromeda Galaxy.

Fraser:  But I guess the question is, did the Milky Way as a Galaxy form super early or is it one of those situations where it has just been a long collection of mergers between Dwarf Galaxies until you got something substantial?  That’s the controversy, right?  

Pamela: Right, well that’s actually not a controversy with our Galaxy.  One of the prior controversies was how the Galaxy is formed.  Is it a top up or a bottom down approach where they either form all at once or they form through the merger of a bunch of smaller objects?  

It’s now thought that some of the largest galaxies in the Universe did initially form right off the bat as giant Galaxies in place.  With our own Milky Way Galaxy we have lots of evidence pointing to the fact that we probably were a merger of lots of smaller things coming together.  We still see small things falling in today.  We’re in the process of eating a small innocent Dwarf Galaxy called the Sagittarius Dwarf Spheroidal Galaxy.  

As we look with the Sloan Digital Sky Survey at individual stars in the Halo around the Milky Way we are able to make out all sorts of different Tidal Streams – elongated streams of stars that were left behind as the small baby Galaxies were disrupted as they fell in.  We talked about this some in the last episode.  

Everything indicates that we probably formed a bit at a time, coming together building our large Spiral Galaxy.  What’s kinda neat is as we look at star formation we can see that not all parts of the Galaxy formed at the same time.  This is more evidence.  The Globular Clusters seem to be some of the oldest objects in the entire Galaxy.  

Also, as we look in at the bar, the bar of the Galaxy is made predominantly of old red stars.  But what’s kinda neat is in the very center of the Milky Way orbiting the Super Massive Black Hole are – depending on who you talk to – either one or two collections of very young stars including about 100 bright blue giant stars.  So we know that there was at least one not too distant burst of star formation in the center of the Galaxy embedded in this bar of old stuff.  

We also see a ring of star formation towards the center of the Galaxy.  The disk of the Galaxy is just full with open clusters of various ages.  The Orion star forming region will eventually be a full-fledged open cluster too.  

Older systems like the Heyedes open cluster are just barely visible as a star cluster because they have spread out so much at this point.  There are stars that are on their final legs.  There are stars that are still forming.  It’s an active and lively population that is mixed in all sorts of different properties.

Fraser:  And so how many of these Dwarf Galaxies, like the Sagittarius one, are recurrently consumed?

Pamela: Every time we have a new American Astronomical Society meeting there seems to be a new press release on new Tidal Stream just discovered.  It’s an ongoing field where thanks to every new data release of the Sloan Digital Sky Survey they get a little bit better and we find a few more of these.  

We’re about to have a new data release so I’m sure there will be more Tidal Streams in the future.  We’re finding these constantly.  There are I think on the order of ten Tidal Streams now known enwrapping the Milky Way Galaxy. 

And there’s the Sagittarius which is just plunking itself into the disk and just dying as it does it right now.  I’d say we know of order of ten and one that is particularly spectacular as it dives into the disk and more are going to be found.

Fraser:  That’s inevitable, right.  It’s an interesting way to do Astronomy – I’m on a completely different tangent here – in the past if you wanted to answer a question, you’d take a telescope and go out and look and record your images and come back and analyze them.  Then you would do your science that way.  

But now, a lot of Astronomy is being done with these surveys, these robotic surveys.  You grind through a database of millions of stars to determine if there are more of one kind of stars in a certain location.  You come out with interesting answers just like that.  

More and more work seems to be done by the surveys of robotic telescopes that gather a tremendous amount of information about the night sky.  Then Astronomers can kinda crunch through and follow their interests after the fact.  A lot of stuff gets done. A lot of analysis of Quasars, discoveries of Asteroids…..

Pamela: It is completely changing how we do science.  It used to be once upon a time any question I wanted to answer I had to go out and basically fill out a bunch of paperwork – because that’s what Astronomers do – and justify to a Telescope Time Allocation Committee attack why I deserved telescope time.  Often I wouldn’t be allocated as much time as I needed to actually answer my question. So I would try to find shortcuts or change my protocol so it wasn’t as good as it could be, all to try and get the very minimum data needed to try and answer my question.  

Nowadays, rather than me going out and desperately pleading with a consortium of people who are going to choose my fate, I simply write a my sequel query and download all the data I need from the Sloan Digital Sky Survey.  It doesn’t answer a lot of questions.  

Once you find something really cool using Sloan Digital Sky Survey, it’s possible to then go to a Time Allocation Committee and ask for one specific question rather than a broad question requiring a ton of telescope time.  It reduces the individual need to get lots of telescope time because you can first go out and use this community survey.  

It’s going to continue to change it as Pan Stars and Large Synoptic Survey Telescopes continue to come online and the amount of data available on the entire sky reaches terabites and terabites per night of newly acquired information.

Fraser:  Thank you for following me on that tangent.  There are two last things I just want to get through.  What is the Super Massive Black Hole?

Pamela: We think that the Super Massive Black Hole in the center is about 3.2 million or 4 million Solar Masses. All that mass is confined to an area smaller than the Earth’s orbit.  

So take the Sun multiply it by 4 millionish and cram it within the Earth’s orbit.  Not only is it crammed within the Earth’s orbit, but we think that it is actually crammed into a space one tenth the size of the Earth’s orbit.  That’s just kinda cool.  

Fraser:  Yeah and I know that some of the most amazing Astronomy was done a few years ago where they were mapping the paths of stars as they orbited around the Super Massive Black Hole.  They just make these U-turns.  A star comes down it makes a quick U-turn and heads off in a completely different direction.  

Nothing but a Super Massive Black Hole, nothing except something with 4 million times the mass of the Sun [Laughter] could crank a star into a whole new direction like that.

Pamela: There are hundreds of stars crammed into the inner parsec or so of Space in the Galaxy, crammed in close to the Super Massive Black Hole.  We’ve been lucky enough to be able to catch some of these making basically fish hooks around that Super Massive Black Hole.  This was the final piece of evidence that allowed Astronomers to say no, it’s not 1,000 neutron stars, it’s not 10,000 white dwarfs or I guess 4 million white dwarfs.  It has to be some singular object crammed into a very small space.  

It’s a beautiful piece of work.  It was all done with infrared imaging but peered through the gas and dust.  It was done with high speed imagers so you could stack the images that were getting distorted by the Earth’s atmosphere such that the least distorted ones from high speed images got stacked one on top another to catch the individual stars.  It’s really amazing.

Fraser:  And the last topic is the future.  You already gave away the ending.  What does the future hold for the Milky Way?

Pamela: In about 4 to 7 billion years we are going to merge with the Andromeda Galaxy.  For awhile we’re going to look a little bit like the merger system called Mice or the Antenna.  Over time we’re going to settle in to probably being a nice Elliptical Galaxy.  We’re going to keep eating our children.  

The large Magellanic Clouds will eventually become part of our Galaxy, not necessarily in that order.  Then over time we’ll probably start merging with other Galaxies in the Local Group.  The Local Group itself is going to join in with the Virgo Cluster and the Virgo Super Cluster is going to grow in mass and consolidate in volume.  

Eventually who knows just how bad it’s going to get – there are those who say it’s all going to be one big Black Hole – I’d like to hold out that there are going to be a few white dwarfs that don’t quite get consumed.  That’s trillions of years in the future.

Fraser:  We’ve done two whole shows just about that.  You can take a look back at those.  Okay Pamela I think we’ve covered our home Galaxy the Milky Way.

Fraser Cain: Last week we talked about Galaxies in general and hinted at the most violent, energetic ones out there. Active Galaxies, specifically Quasars have been a mystery for more than half a century. What kind of object could throw out more radiation than an entire Galaxy?

A Black Hole, it turns out with a mass of hundreds of millions of suns can do this feat. Let’s trace back the history of Quasars and find out exactly what they are.

So Pamela, I actually find the history of Quasars really interesting because it was this amazing discovery and they had no idea what was causing it.

Dr. Pamela Gay: Well you’re exactly right. This is one of those things that really confused people for a while. Back in the 1950s we started looking at the skies through radio telescopes. We started to realize that even objects like Jupiter emit light in radio waves and if you tune a radio dish to the right color of radio light and look around the sky you can find all sorts of cool objects.

One of the common wavelengths to look at is about 20 centimeters. But there is everything from millimeters to many meters long that we look at as we try to gain more information about these objects. In one of the surveys that is now affectionately referred to as the “3C Catalog”, they found all of these little point sources of radio light around the sky.

They started following them up with progressively larger telescopes and found that some of these points of radio light were actually associated with points of optical light. But they were fairly faint so they started looking with spectrographs. They were questioning what they were seeing. What type of star were they looking at?

When they looked at them, they saw emission lines. They saw patterns of lines that didn’t match any known type of star and there was a lot of head scratching. There were a few people who made early claims that it was just something at really high red-shifts. It took awhile before someone was able to look at these lines and recognize the pattern of hydrogen.

Fraser: Right but to say something was at really high red-shifts when what they were seeing was something moving away very quickly, right?

Pamela: Yes, that’s exactly right. Astronomers like to sometimes confuse our terminology. It’s not really very friendly of us. When we say something is at high red-shift, what we mean is that it is moving away from the planet Earth at an extremely large velocity. As a result of its motion we see that the color appears to change and appears to move toward the red.

This reddened light is just part of the Doppler shift. It’s the same thing that affects sound when a fire truck passes your house and you hear the pitch appear to change.

With Quasars, these are objects that are billions of light years away and some of them are red-shifted sixteen percent. This means that the color is sixteen percent of what it should be. Some of these objects are moving 37, 38 or more percent of the speed of light as you look at things further and further out into the Universe.

Fraser: So Astronomers noticed all of these points that look like stars but when they analyzed the spectra of them, they were moving like a Galaxy really far away.

Pamela: And at the time, we still weren’t consistently able to find Galaxies at that high of a distance. This is one of the things that really confused us. Here are these points of light that seem to correspond to the edge of the Universe and they were so bright. They looked like stars and they didn’t have morphologies that looked like any type of Galaxy we’ve ever seen.

There was a lot of head scratching. It wasn’t until about 1962 that we figured out that these lines are the spectral lines of hydrogen. These are objects that are moving more than 40,000 kilometers per second away from us and this is some sort of new Physics, some sort of a new object.

It was only in the 1980s that we started to build big enough telescopes to look at these points of light and see that the point was just the center of a very distant Galaxy. It now appears that at some point in their history probably just about every type of large Galaxy could have been a Quasar.

Fraser: And the term Quasar comes from?

Pamela: It’s actually an abbreviation. These things were found in the radio. They looked like stars. But they weren’t so we called them Quasi-stellar Radio Sources. But that’s a pain to write out so a fellow by the name of Hong-Yee Chiu pointed out this is a lot of words to write so let’s abbreviate it to Quasar.

Some of these objects don’t actually give off radio light so we call those QSOs – Quasi-stellar Objects, which isn’t nearly as much fun to say. So the name Quasar is the one that is most frequently used.

Fraser: So with the advent of more powerful telescopes Astronomers were able to actually see that these weren’t just really bright star-like objects in the sky but they actually were at the heart of a Galaxy.

Pamela: These were the cores of distant spirals. They were the cores of distant ellipticals. These were just regular Galaxies that for whatever reason had an angry monster in their centers.

Back before we even knew for certain that Galaxies actually had super-massive Black Holes in their centers; we knew that there was some sort of angry physical entity that was rapidly spewing out more energy than anything else in the known Universe.

Fraser: And just to give some amounts out, a Quasar can put out as much energy as the rest of the Galaxy, right?

Pamela: It can put out more energy than the rest of the Galaxy. That’s one of the cool things about it. Take all of the energy in the Galaxy, up the ante a little bit, and you start to get the brightest of Quasars.

Fraser: Wow. Okay, so they’re starting to realize that there is some kind of exotic object, something at the middle of the Galaxy that is pouring out all of this energy. When did the Black Hole connection finally come back?

Pamela: People started to make guesses about that in the 1980s once we started to realize that these were objects at the center of Galaxies. But the first super-massive Black Holes weren’t confirmed until the mid-90s. There were a lot of talks between the mid-80s and mid-90s where Astronomers stood up there and talked about the angry monster and that was actually the phrase that was usually used in scientific talks: “The Angry Monsters in Centers of Distant Galaxies.”

They talked about how you could generate this with the Black Hole. There are actually a lot of different pieces of evidence coming out from many different directions. In the most distant parts of the Universe we had Quasars with enormous brightness. Sometimes these objects would be a hundred times the brightness of the Milky Way all compacted into the center of a distant Galaxy.

The other thing that we knew was they were capable in some instances of varying in brightness very rapidly. When you have rapid variation that means you can’t be dealing with a large object.

One of the things that happens is if you take a light and you embed it the center of a media and you turn the light on and off, the light is traveling both toward you and backwards through the media. It’s going to reflect off of it and come back at you later.

The first light that you get is from when the light is originally turned on and it starts propagating straight towards you. Now you turn the light off and you’re still going to keep getting light for a while. The last bit of light that you get is the light that comes from the furthest back edge of that object that hit the back edge of the object and then reflected back towards you.

Fraser: I understand, you’ve got almost like a ball around the center and you see the light coming down from the front side of it. You’re also going to see reflections off of the back of that imagined like some sort of silver ball. So the last amount of light that you will see is the light that is bouncing off the back of that.

Pamela: So the shortest flicker you can possibly see is defined by the size of that object. With these active Galaxies we see flickering that seems to indicate we are dealing with an object maybe only the size of the Solar System.

So you have something that is roughly Solar System sized and is also giving off huge amounts of life. This is really confusing and pretty much the only way to do this is to cram a Black Hole in there, it’s the only thing dense enough, put an Accretion disc around it (a disk of dust and gas and other material that is streaming in towards the Black Hole) and try to jam that material into the Black Hole so quickly that the Black Hole gets jammed up and magnetic fields form.

You start jetting the material out the rotational axis of the Accretion disc. If you put all of these pieces together, you start to get the things that we identify with Quasars. You start to get the amazing amount of luminosity. You start to get the fact that these things don’t look the same at all angles.

Some of these give off radio light while others don’t, which is probably an effect of the angle we are looking at them. If you’re looking at a system straight down the jet, straight down toward the Accretion disc such that the Accretion disc would appear like a plate down at the base of this jet, then you will get all the radio emission.

If instead you are looking at the system sideways, such that the radio jet goes straight up and straight down on your image of the sky, the rest of the Galaxy will probably block the central radio emission. That’s how you end up without getting radio luminosity as you look at it. It’s all different affects of angle and of how much feeding is going on.

The other clue that these might be something unique to the edge of the Universe that fits with our cosmological models is Galaxies had more dust and gas when they were younger. Over time this gas and dust clearly fell into Black Holes. It also was wrapped up into star formation.

So as we look at the nearby Universe we don’t see any Quasars. We also don’t see systems that have a lot of gas and dust down in the centers of the Galaxies. This fits with the model where early in the Universe we had these Galaxies forming and they had too much gas and dust and all of this material fell in towards the center of the system and lit up an angry monster, an angry super-massive Black Hole that was feeding. This created these radio jets, dense regions of emission that flickered and changed over time and that we now see as these highly variable objects.

Fraser: There is one last really important piece of data that was uncovered in our own Milky Way, right?

Pamela: Yeah, as we look out and start looking at the high-energy gas around our own system, we see shock waves that look like sometime in the past our own Milky Way was indeed a Quasar. Echoes of this angry history are still out there being discovered.

You can almost imagine this amazing period in the Universe when all of the Galaxies were lit up like Quasars and everywhere you looked all of the Galaxies were these bright shining nuclei of jets and radio, and gamma ray and x-ray emission. Once going through this terrible Quasar phase everything calmed down to the normal Galaxies that we see today.

Fraser: So let’s talk a bit about the phases then. I know that the thinking right now is that the super-massive Black Hole and the Galaxy kinda seem to grow together.

If you have a big Galaxy it has a big super-massive Black Hole and if you have a smaller one then it has a smaller Black Hole. And so the Black Hole goes through phases, right? What sets it into an active feeding phase when we see the Quasar?

Pamela: It needs to be eating something. This is one of the cool things about looking around the modern Universe. We may not see these things that have two trillion times the energy output of our Sun, but we do see Galaxies that have active Black Holes in the center that are giving off radio emission.

These systems are often irregular systems that are in the process of consuming things, or that sit in the very center of Galaxy Clusters, places where they are getting extra gases and dust from somewhere.

What seems to dictate the anger – to abuse an adjective I shouldn’t – of a super-massive Black Hole what seems to dictate the luminosity of the Accretion disc in the jettison material it is giving off is the rate at which it is consuming material.

Today we don’t have as much stuff to feed a super-massive Black Hole. However, you can imagine a point in the future where when Andromeda and the Milky Way collide.

What gas and dust is left in our two systems will be shocked into both forming stars and plunging into the two system’s central massive Black Holes and as it does that our two different super-massive Black Holes are going to come to life. They are going to become active. There will be bright nuclei in the centers of our two Galaxies that over time are going to coalesce and over time those Black Holes are going to coalesce.

We can see this as we look out at other emerging Galaxies – the Mice for instance. They have active Black Holes in their centers, bright cores of light in what’s left of their two nuclei. It’s a whole range of objects. “Active Galactic Nuclei” is the parent term. It incorporates everything from M87, a Galaxy in the center of a cluster that is giving off amazing radio jets. It is an elliptical Galaxy whose central Black Hole is angrily feeding on gas and dust and it sits in the center of a high-energy x-ray emitting cloud of gas.

There are other systems such as BL Lac a Galaxy that was originally thought to be a star that was a variable. It’s a Galaxy that has amazing jets that are pointed almost directly at us and we see the center of the Galaxy flicker and change with light over time as the Accretion disc fluctuates with time.

There’s a whole range of objects. We have too many different names because we originally didn’t know these were all the same thing. For instance there are two different types of systems called Seyfert One and Seyfert Two.

Early on when I was in graduate school people made a big deal about how these were two different systems and one had only narrow emission lines, bright thin spikes in their rainbow where one particular color was given off more than any other. Seyfert Ones had these bright narrow spikes but they also had bright broad spikes. You get narrow lines when something isn’t moving that fast. You get broad lines when something is moving extremely fast.

The Seyfert Twos didn’t have these broad lines. They only had the narrow lines. People made a big deal about how these were different systems with different physics. But then slowly a picture began to emerge where we realized that the broad lines, this was when we were looking at material that was close in to the super-massive Black Hole, material that was moving extremely rapidly and the stuff on the left edge would be moving rapidly toward us and the stuff on the right edge would be moving rapidly away from us.

We would see this line, this particular color of light get both red-shifted and blue-shifted depending on where it was in the center of the Galaxy. Whereas the narrow lines came from looking at material that wasn’t moving quickly, material that was further out. So you only got both broad and narrow lines when you could see all the way down into the center.

Fraser: So, you’ve gone over this a few times but if you can imagine a Galaxy with a super-massive Black Hole at the center and the super-massive Black Hole is rapidly spinning, it has magnetic fields around it that are interacting with all of the gas and dust that it is feeding on. Then around that there is like a ring or a donut of dust that obscures the Galaxy, right?

So if we see it, and I know that the angle can really matter on what we think we’re looking at right? If we see right down into the Black Hole then we don’t see that obscuring donut of gas and dust around it. It’s like we’re seeing it almost directly, right?

Pamela: The model that gets used a lot is actually one of these foldout Christmas or party decorations you can get. They’re fan-shaped with a pivot point in the center. We’ll put a link to one of these things on our website so you can buy one at the local party store if you want.

When you fan them out, they have a very narrow center and then they get wider out towards the middle, as in middle of the distance from the center to the edge. Then they get thinner out towards the edge.

So, you have this three-dimensional disk. The center of the disk is basically a few millimeters thick. Out halfway from the center to the edge it is many millimeters thick. Then it gets thinner again.

If you hold this thing you can tilt it such that the thick part that is near you blocks you from being able to see the very center, the thinnest point of the disk. You can still see some of the stuff back beyond it.

It’s this three-dimensional shape that is thinnest in the center and then gets wider as you move away from the center that we think represents the Taurus of the center of one of these Galaxies.

So, you have the gas and dust of the main part of the Galaxy that obscures your ability to see in toward the center. The Accretion disc itself has structure so you’re basically looking at this disk of random distribution of matter in it. It’s a disk. It has spiral arms and it all depends on how things are lined up what part of the core you’re able to see.

Fraser: But we can look right down the throat of it and see the Black Hole pouring out the radiation or we can see it from the side where this disk is completely obscuring the Black Hole.

Pamela: It’s the angles in-between that make life interesting.

Fraser: Right, but isn’t that where the classifications come from, whether it’s a Seyfert Galaxy or a Quasar or I know they have some other names as well.

Pamela: Well, Seyfert One and Seyfert Two seem to come from what angle you look at it. Quasar is something that is feeding at an enormous rate. Quasars are sort of taking any of the other active Galaxies, turn up the mass consumption level, and you can turn them into a Quasar.

Turn down the mass consumption level and you start to get things like the Seyfert Ones and Seyfert Twos, which are generally spiral Galaxies or irregular Galaxies. You also end up with just plain active Galaxies like M87. It’s an elliptical with jets. It’s a radio Galaxy.

We try to make the definitions we use based on physics. The physics that we’re looking at for things like this are if you call something a Blazar. That is something that you’re looking straight down the throat of the jet. You’re looking straight in at the Black Hole. If you call something a Seyfert One or a Seyfert Two, you’re talking typically about a spiral or an irregular Galaxy that you’re able to see varying amounts of the center and that changes the definition of what you’re looking at.

The energy matters, whether it has radio emissions or not does matter. We have dozens of words that we use to describe these things and put them into little tiny, tiny bins.

The important part is Quasars have lots of luminosity, active galactic nuclei that includes the Quasars but most of the time you are talking about things that are a little less violent.

Fraser: The measurement is just how much material is being consumed today.

Pamela: Yeah.

Fraser: And if you could look back in the past things might be Quasars a million years ago but not be Quasars today. Or, things might become Quasars in the future. It just depends on when things happen to fall into the center of the Galaxy. And it often happens after you have these collisions.

Pamela: This is what keeps the Universe interesting. It hasn’t always looked the same. So as we look at more distant objects, we see more Quasars. As we look around today we still see the radio Galaxies.

They’re close enough that we can start to get a detailed view of the basics of what’s going on. They’re not quite as violent today as they used to be. The Universe is a bit more peaceful today.

Fraser: Now if our super-massive Black Hole at the heart of the Milky Way went into an active feeding phase what would we see?

Pamela: Well the Sagittarius Constellation would sure light up a lot. We’d see it as a combination of different things. There would first of all be a whole lot more optical luminosity.

We’d also see what is called synchrotron emission, which is a type of radio light that comes from accelerating electrons. We would see x-rays and gamma rays from all the material being heated up in the Accretion disc.

All of these different things would also light up the dust and gas in the center of the Milky Way making it pretty much impossible to see through to the other side as everything was lit up more and more.

We’d be safe. Luckily we’re in the disk of the Galaxy so any jets that happen to have formed would be pointed in other directions. It would certainly be an amazing light show.

Fraser: Right. I know that we get little hints of it every now and then when something even fairly small like asteroid-sized chunks of material drop into the super-massive Black Hole let off so much energy.

Pamela: Yeah, there’s definite x-ray flickering that we see and occasionally you’ll see reports of planet-sized objects falls into center of Milky Way….

Fraser: Yeah, it’s almost like they’re tracking them now. They can report that something this big fell in on Thursday [Laughter] and they will see reflections. They can even know when larger things happened hundreds of years ago because as we talked earlier, you get these reflections coming off of the gas around the super-massive Black Hole.

So, you’ll see almost like light beams moving through this material and you think oh yeah, that was like 200 years ago when that burst happened. It’s quite amazing.

Pamela: We can keep track of the destruction of things in this way and watch the flickering. It is really amazing how much we can learn about the center of our Galaxy today by looking at the material around it and by looking at how materials orbit around it.

There are some amazing videos out there online. A lot of them are by a woman named Andrea Dupree who has been tracking the motions of stars in the inner part of the Milky Way for well over a dozen years now.

She can see these objects in their quick turn around motions around a central object that has to be exceedingly small to explain the closeness that the stars are able to get to it.

We know there’s a super-massive Black Hole there. There’s no longer any observational doubt. Nothing else could fit into so small of a space. We watch the x-ray flickering.

Our first hint that our Galaxy had a super-massive Black Hole was this anomalous x-ray object that we call the Sagittarius A*. We now know that it’s coincident with the object that Andrea is able to see in her observations.

Fraser: And so we’re absolutely safe from our super-massive Black Hole? Even if it turns into a Quasar?

Pamela: Well, I don’t see it turning into a Quasar. We don’t exactly have that much gas and dust hanging out. We should be safe.

Fraser: All right, good. I think next week we’re going to take a look at another Galaxy our own home Galaxy the Milky Way.

This transcript is not an exact match to the audio file. It has been edited for clarity. Transcription and editing by Cindy Leonard.

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Fraser Cain: This week we are going to look at some of the biggest objects in the Universe: galaxies. It was the discovery of galaxies in the early 20th century that helped astronomers realize just how big the Universe is and how far away everything is.

They learned how galaxies formed, how they evolved and changed over time, merging with their neighbors and what the future holds. Now, you know a lot about galaxies, don’t you Pamela? This is like one of your specialties, right?

Dr. Pamela Gay: It’s one of my areas of research. I did my Master’s Thesis studying the Ursa Minor Dwarf Spheroidal Galaxy which is one of the smallest ones out there and deciding to mix it up a bit for my dissertation, I worked on studying galaxy clusters.

Currently I’m working on a project with a graduate student and Chris Lintott of Galaxy Zoo among other things to study galaxy clusters in the Sloan Digital Sky Survey.

Fraser: Crazy.

Pamela: They’re fun.

Fraser: Well, let’s start with a galaxy that we’re fairly familiar with, Milky Way, and then see how we got here from there over the lifetime of the Universe. [Laughter] So can you give us some dimensions of the galaxy that we live in and then we’ll go from there?

Pamela: Our giant galaxy wasn’t always one beautiful, glorious spiral system. It actually started out once upon a time as a lot of smaller galaxies, elliptical galaxies of various forms that emerged out of the small irregularities in what we now see as the cosmic microwave background. These small galaxies merged together. Gravity pulled them together.

Because different sections of the Universe tended to have motions that were in similar directions, you ended up with a lot of things coming together and joining in a way that they ended up spinning a lot like pizza dough that gets thrown into the air is spinning. That spinning motion caused them as they collapsed and coalesced together to form a disk of material.

Fraser: So, after the Big Bang, we have these irregularities in the density of everything that remained. Material started to pool together, turned into stars. The stars were gravitationally attracted to each other and formed little irregular blobs of stars.

Those blobs came together into larger and larger collections. After enough of them came together, if you added up all the motions of all the stars, you ended up with this spin and that’s how they disked out, right as opposed to being a bit of a ball.

Pamela: Most of the way there. There’s one curiosity though. We don’t know which formed first, the galaxy or the stars. There were these pockets, dark matter halos of gas and material that we believe started to collapse and form the dwarf galaxies. At the same time, these pockets of material are solidifying out of the murk of the Universe.

These stars started forming inside the pockets. So, the galaxy just sort of came together all at once with the stars forming in these pockets. You ended up with an entire galaxy of star formations.

Fraser: Wasn’t the dark matter almost acting like a funnel?

Pamela: A box.

Fraser: A box, yeah. That was the dark matter. Once that was in place, that’s what pushed all of the matter and pulled it all together to form the structures that we see. With all the dark matter it all would have just flown away, right?

Pamela: One of the crazy things about the Universe is that while we’re pretty sure that galaxies like our own Milky Way formed from a whole bunch of small galaxies that formed independently and then gravitationally merged to form the Milky Way, we think that some of the largest galaxies in the Universe formed in situ as they were giants from the beginning.

That’s kinda cool to think about that the largest irregularities in the original stuff of the Universe just sat there and said “Hi, I’m going to be a giant galaxy”.

Fraser: Right and that’s kind of overturning a lot of the thinking which as you mentioned with the Milky Way was merge, merge. Small galaxies coming together, bigger, bigger and bigger until you get like a big classic spiral.

With the dark matter doing the pushing of the material together, you could just get it all coming together in one fell swoop.

Pamela: What’s crazy is just to watch how all this has evolved in just the past ten years. When I was a graduate student taking classes on galaxies we talked about if it was a top down or a bottom up approach or do you get big thing and big thing forms. Or, do you get a bunch of small things that fall together.

Now we’re realizing it’s not an either or, it’s an and where at the very beginning of the Universe you did end up with this giant galaxy forming in one place. And you ended up with smaller galaxies forming that merged to form progressively larger structures that eventually formed more giant galaxies.

Fraser: So as we got to the point where the galaxy has spun up and has flattened itself out into a disk. Where would that have been in the history of the Milky Way?

Pamela: Timing we’re still trying to sort out. As we look back at larger and larger red-shifts, we see things start to lose their structure. We’re not sure at exactly what moment spiral galaxies started to turn on but it was probably in the first few billion years of the Universe.

As we start to get new telescopes like the James Webb Space Telescope, we’ll be able to peer at the earlier moments of the Universe with greater clarity and be able to determine at what moment in time when you look in the infrared you see galaxies that are fragmented in structure or irregular in structure.

As you look at things that are more and more recent at a given point in time spiral structure starts to turn on. We’re still sorting out when in time you ended up with pretty spirals.

Fraser: But I recall writing stories where the age of that keeps getting set earlier and earlier.

Pamela: This is the crazy thing. This is why I’m hedging saying anything because the James Webb isn’t there to answer it for us yet. As we get more and more high resolution images coming out of various telescopes and spacecraft, we’re starting to find that galaxies formed earlier than we thought and giant galaxies formed earlier than we thought.

I think that this is something that any number that is in your textbook you shouldn’t believe until James Webb has had a good look at the Universe.

Fraser: Right, we’ll just add this to the list of textbooks that are wrong. Lies my textbook told me. [Laughter]

Pamela: What’s cool though, as we look back we’re finding these theories we’ve had are proving to be true. As we look back in time we see the irregular galaxies. We see the smaller galaxies. We see the star formation that gets triggered with them coming together and shaken up through the collision.

Our understanding is proving itself to be true and that’s always a good thing. I really like the fact that this is an ‘and’ which means the two theories that we were all forced to learn in graduate school were not a waste of our time.

Fraser: So they could both be right. Galaxies could form zip or they could be the slow accumulation of material over long periods of time.

Pamela: And that’s just cool.

Fraser: And we do know that there is this slow accumulation because the Milky Way is in the process of consuming neighbors today.

Pamela: Yeah. The Sagittarius Dwarf Spheroidal Galaxy is in the process of being actively consumed by the disk of the Milky Way. As we look out with surveys like the Sloan Digital Sky Survey and map out the densities of stars in the halo of the galaxy it seems like at every big science conference there is the announcement of a new tidal stream. A new stream of stars representing the death of a dwarf galaxy is being found in the halo of the Milky Way.

Fraser: And this is when they look out and see a whole bunch of stars that all have kinda the same age and all the same kind of chemical constituents and assume that they all started as part of the same galaxy and if it’s arrayed in a big long line that says tidal tail.

Pamela: Basically what’s happened with these systems is you have a small blob of stars. In some cases they have no more mass than the pretty globular clusters some of you probably look at with your telescopes. Some of them aren’t all that much bigger than say M13 except when you start counting the dark matter.

In terms of stars, they’re not that much bigger but they have a lot of dark matter in them. These small blobs of stars with a lot of dark matter in them as they orbit around our galaxy, some of them have death spirals.

At a certain point as they get closer and closer to the center of the Milky Way, the gravitational pull on the leading edge of the galaxy that is falling in and the gravitational pull on the far side of that galaxy the difference between the pull on these two points is greater than the gravitational force holding that cluster together.

You can sort of imagine that you’re pulling on the front edge of a piece of pie that is sitting on the counter and is not in an aluminum plate. If you yank too hard on that piecrust, you will get a handful of pie because you pulled harder than the molecular bonds of that pie held the pie together. What you’ve done is disrupted the pie.

As that spiral galaxy that is meeting its doom falls toward the Milky Way, the Milky Way’s gravity reaches out and grabs the leading edge of that galaxy and gives it a good yank and disrupts the galaxy. This disruption leads to these beautiful tidal tails. These beautiful streams that are the relics of what used to be systems and over time the stars in those tidal tails are going to fall into the Milky Way and be randomly distributed such that you’ll no longer be able to see that this group of stars used to be one galaxy. Instead you’ll just see a thicker halo of stars around the Milky Way.

Fraser: But wouldn’t the addition of all these galaxies that are likely going in completely different directions sort of mess up the Milky Way’s beautiful spiral? Wouldn’t at some point you would just get a mixture of directions?

Pamela: Well, this is where you have to look at all the different parts the galaxy has. In fact, the in fall does affect the Milky Way in rather dramatic ways. When it comes to simply disrupting the pretty spiral structure the mass that’s falling in isn’t that much.

When you compare the size of a dwarf galaxy that might have a few thousand or tens of thousands of stars compared to the Milky Way with its billions of stars, looking out, we’re not going to see more than perhaps the nucleus of the Milky Way gets a little bit bigger and a little bit bigger. What we do end up seeing that is quite dramatic is systems that have larger companion galaxies that are contemplating death. Like our large and small Magellanic Clouds. These larger nearby neighbors can generate all sorts of really cool features in a disk galaxy.

We talked about this in an earlier show. In our own Milky Way Galaxy, we have a bar at the center of the galaxy. If you could get outside of the Milky Way and look down you would see nucleus and coming off the nucleus a straight line. Off the ends of this line is where the arms finally emerge.

Structures like bars or rings in the center of galaxies are all generated by nearby companions. You see the same thing with M51, the whirlpool galaxy. So the in falling companions can generate neat features. They also can cause the disk of a galaxy to warp. When you look at a disk galaxy and you see the disk isn’t flat but is rather twisted sort of like a sheet blowing in the wind.

Fraser: I’ve seen lots of those pictures of the warped disks. It kinda looks like someone left a record out in the sun for too long and it has this tweaked warp to it. [Laughter] Now what are some of the things that happen to galaxies as these mergers start to happen? I know there are bursts of star formation…..

Pamela: It all depends on the size of the system that is being eaten. If you just have a little dwarf galaxy coming in most of these systems have no gas or dust. Mostly what they have to contribute are senior citizens stars and dark matter. We’re not going to notice the dark matter except by the rate at which stars end up rotating around the Milky Way. Things start going a little bit faster. That’s the biggest difference. The stars coming in, yeah we now have some extra stars in the halo but it really doesn’t do much.

Where it starts getting cool is where we are getting larger and larger galaxies falling in. As we start getting larger dwarf spiral galaxies instead of these little baby dwarf spheroidals, or you start getting irregular galaxies like large and small Magellanic Clouds hitting the halo of the Milky Way, it shocks the gas and dust in these systems and starts triggering star formation. You can end up with elliptical galaxies that are bright blue with star formation.

You can end up with knotty systems where you have pockets of nebulas and stars all mixed together in this heap that has no noticeable structure of any sort, no spirals, no nothing and they look absolutely incredible.

The most spectacular objects in the Universe are nebulas and colliding galaxies. If you take a baby galaxy and collide it with a big one and you get both nebulas and star formation. This is what makes large and small Magellanic Clouds so cool to look at.

Fraser: How much star formation will go on compared to just like a normal galaxy is?

Pamela: It depends on how much gas and dust is in the system that’s colliding. When the Milky Way and Andromeda somewhere in about five to seven billion years get around to knocking each other about in their gravitational dance, all of a sudden all the gas and dust that is left will simultaneously start forming stars or fall into the super massive black holes at the centers of our two systems.

You will get simultaneously angry feeding black holes and star formation that can be hundreds and hundreds of times greater than what we normally experience. You’ll end up with Super Nova going off. You’ll end up with black holes, potentially jets, radioactivity…it will be spectacular to look at.

Exactly how big, bad and bright things get we have yet to figure out. If you look at the Mice, one of the more prominently featured in images, sets of colliding galaxies, that system may not be too different than what we’re going to experience.

Fraser: The Mice is a pair of colliding galaxies, right?

Pamela: Two spiral systems not too different from our own that have been imaged by just about everything. There is a really cool catalog of galaxies called the Arp Catalog of Peculiar Galaxies that contains a lot of colliding systems and the Mice are one of the systems in there. They’ve been followed up over the decade since including by the Hubble Space Telescope.

Fraser: What does the future hold? We look out into the Universe and we’re only really looking back in time because light takes time to travel and so everything we see is like this great big time machine that lets us see back. But, what does the future hold for the large spiral galaxies in general?

Pamela: Well in general, everything dies. That’s the sad part of astronomy. We have all these magnificent events where the physics is just hard to take in with the energies, the temperatures and everything that’s going on and all of it leads to one result: the end of star formation.

After the Milky Way and Andromeda collide there will be a terrific burst of star formation. Afterwards all the fuel will be used up. All of the building materials will be used up. Because our spiral galaxy and the Andromeda spiral galaxy aren’t spiraling in the same direction, the collision is going to throw together a lot of stars with very different orbital paths. We will end up eventually forming an elliptical galaxy.

Eventually we’ll probably end up colliding with more galaxies the size of our own forming an even bigger elliptical galaxy. As we look out at some of the denser regions of space, galaxy clusters, and groups bigger than our local group in some cases groups that contain thousands of galaxies what we see is interactions between galaxies always lead to death.

It doesn’t always have to be a head on collision like we get with Andromeda. You can also have just random friendly blue galaxy bright with star formation, friendly with spiral structure falling into a rich galaxy cluster. As it falls in, this rich galaxy cluster has so much mass that all the galaxies in it are moving rapidly.

About every billion years it might end up with another galaxy blowing past it at high velocity. Even though the two systems don’t collide, the gravitational tug of the other system will yank stars, gas and dust out of the friendly little blue galaxy and its blueness will fade to red as it loses the dust and gas necessary to form stars. Its spiral structure will go away, all these gravitational whacks destroys its structure.

Eventually as it plunges into the densest regions of the cluster where you end up with basically, as far as the Universe is concerned, thick gas in the center of the cluster, just the shock of hitting that gas will kill whatever star formation was left. In just a few billion years you can kill a galaxy.

Fraser: Right, so you force a galaxy to just use up all of its fuel in one great big burst of star formation or you blow its fuel out the…[Laughter]

Pamela: Out the wazoo!

Fraser: Yeah. If you impact it with something else, you can separate the gas from the galaxy itself. The point is you use up all of its fuel and there can be no new stars and then all of the really massive stars detonate a super nova or die quickly. All you are left with are the red stars.

So, that’s what we see then these big, huge balls of stars, many times the mass of the Milky Way. They are balls of stars because they have added up all the random motions of all the galaxies and they haven’t flattened out into a disk and they’re red. All they have is just old red dwarf stars left, right?

Pamela: And lurking at the center of these giant elliptical galaxies are giant super massive black holes. And in some cases, M87 is one of the most famous cases, the gas and dust of an entire cluster as it settles toward the center of the cluster.

Sitting in the center of that cluster is often a very special type of elliptical galaxy that we call a CD galaxy (for lack of creativity). The CD galaxy may be alive with an active black hole in the center that is spewing jets of material out of the two ends. The shock from these jets hitting the gas and dust that is settled into the center of the cluster heats that material up.

As you start to look at the Universe with our x-ray glasses, we look out using Swift, using all the different x-ray imaging telescopes out there, what we end up seeing are knots of gas that are many thousands of degrees in temperature emitting x-rays. This really hot gas can never coalesce back into stars or anything that would allow structure to form.

Over time, the Universe will cool and over time, this gas and dust might be able to do something useful on its way to probably landing in a super-massive black hole. But for now it’s just hot and sitting there emitting x-rays. It’s in a place that it was stripped out of the galaxies and is no longer useful fuel or building materials.

Fraser: Were there any kinds of galaxies out there that we haven’t talked about yet that people might want to know about?

Pamela: Well, the main classifications of galaxies are elliptical, lenticular galaxies, which are galaxies with identity crises. They’re basically disks of stars that have lost spiral structure and then you focus your telescope and realize there is no structure, flat pancakes with no structure.

Then there are the spiral galaxies, the ones that are the most photogenic with their arms. There are the irregulars that I talked about. They have gotten whacked pretty hard and have massive structure.

It’s when you start looking at the sub-classes of these objects that you start to get really cool things. There is what is called Seifert galaxies that have active black holes in the center and are giving off lots of radio light. We can look at these things and in some cases see pretty cool radio jets, radio in the center.

What we think is happening is the black hole in the center is actively feeding and as it’s feeding it’s giving off emission. How we see that emission depends on what angle we view the galaxy at. If we’re looking straight down the top of the galaxy, looking in at the anger super massive black hole, we see one set of radio emissions. If we see the whole system edge on, we see something entirely different. So we call these Seifert one and Seifert two – for lack of creativity.

Fraser: Isn’t another name for that a Quasar?

Pamela: This is where we start getting into what are the gradients? There are all sorts of different galaxies that fall into the category of active galaxy. The Seifert one and Seifert two aren’t as powerful as a quasar. We think they’re a family of objects. We’re still working on unifying all of our different understandings as we start to get more space-based telescopes and get higher resolution telescopes here on the Earth.

Quasars are really actively feeding black holes. Such that when you look at them, the nucleus of the galaxy appears to be brighter than the entire rest of the galaxy. In some cases that nucleus is so much brighter that as we look at the system we just can’t get at “where is the galaxy surrounding this nucleus.” This is also why they’re also called quasi-stellar objects – QSO because they appear as point sources in a lot of images.

Fraser: Well, we’ll to a whole show just on Quasars. [Laughter] Don’t give everything away.

Pamela: If you then have a black hole that’s a little less energetic in how much it’s eating, that’s where you start to get down to radio galaxies that aren’t quite as active. You have the Seifert ones, the Seifert twos that are probably the same physics of what we call quasars, but there are different emission lines that appear. There are different properties, cut-offs in the amount of radio emission that come out. This is where we start getting to the actual use of the words radio loud.

As we look at these systems, there are lots of different characteristics and we’re still building a unified picture of taking the same object and looking at it sideways and head-on, these are the differences you see, versus “these are two different things and the physics in them is intrinsically different.” We’re still sorting all those bits out.

The Universe is cool. It has lots of unanswered questions. As you start looking at the Universe and galaxies in particular across radio x-ray and optical light and bringing in the infra-red for flavor, one galaxy can look dramatically different in all these different wavelengths.

Fraser: I want to touch on something that we’ve talked about already is what role does dark matter play on this? It seems that since dark matter was first discovered, it’s been playing more and more of a role in galaxy formation and evolution and everything.

Pamela: This is where we struggle. We know that the luminous matter in galaxies is embedded in what we call dark matter halos. We’re still sorting out what is the density profile. Is it denser in the center? How does it fall off? Is it denser on the outsides?

We’re starting to get a feel for these things. There are lots of pretty plots that show how the luminous matter falls off. Here’s how the dark matter is distributed through the system. We have a feel for these things. What’s cool is we’re also finding that you can have a glob of dark matter that doesn’t have a luminous matter in it. We find that through gravitational lensing.

All luminous galaxies have dark matter halos but it’s possible that there are also just blobs of dark matter hanging out by their lonesome without any stars embedded inside of them. These dark matter halos probably formed first. Their gravitational attraction caused the luminous matter that might not have had quite as lumpy a distribution.

We’re still sorting out how all of this works, how is it that the dark matter is formed first. These dark matter halos then collected luminous matter in their centers. What’s fascinating is not all systems have the same ratio of light matter, luminous matter to dark matter. As you look at the dwarf Spheroidal galaxies, they have much more dark matter. As we look at the larger systems, they have less. We don’t know why.

Part of it could be that Super Nova blasted all of the gas out of the dwarf galaxies but why is the dark matter still there? It doesn’t interact, that’s part of the answer. But why did they form with all of this dark matter to begin with? We don’t know all of these answers. We’re getting at facts and once we have accumulated enough facts, the theorists can start figuring out what it all means.

For now we’re going out and when we see something, we measure the ratio of luminous matter to dark matter there. We continue the process as more are found. Let’s in detail map out what rate are the things we can see moving as a function of radius of galaxies. How fast are the stars in the centers of galaxies moving compared to those a third of the way out or half way out or at the very edges?

Making all of these measurements allows us to get luminous matter to dark matter ratios to get the distribution of dark matter as a function of radius. As we look at all of these factors for more and more different shapes and sizes of galaxies, hopefully we’ll be able to figure out where all of this stuff came from.

Fraser: Right, but I think it sure seems like just because we can only see regular matter, we can only see the luminous matter, we focus on that. But it’s almost like some alien or advanced culture would say dark matter is what you think about. [Laughter] The luminous stuff is just the pesky crumbs around the dark matter which is the serious thing to think about. Okay, I hope that gives our audience the overview of the galaxies.

I think we’ll do a show on the Milky Way specifically and Quasars as well in coming weeks. I think we can then focus on them. Quasars and the Seifert Galaxies are so interesting topics about what is going on at the very heart of our galaxies.

Pamela: So, from Mars to the Milky Way. [Laughter] That’s a good journey.

Transcript: Cosmic Rays

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Fraser Cain: We’re going to return back to a long series of episodes we like to call: Radiation that Will Turn You Into a Superhero. This time we’re going to look at cosmic rays, which everyone knows made the Fantastic Four.

 

These high-energy particles are streaming from the Sun and even intergalactic
space, and do a wonderful job of destroying our DNA, giving us radiation
sickness, and maybe (hopefully!) turning us into superheroes.

 

Pamela?

Dr. Pamela Gay: No.

Fraser: All right.

 

[laughter]

 

I guess we’ll have to wait for the next episode – perhaps gamma rays. We’ll
keep moving.

 

So where do cosmic rays come from?

Pamela: They come from as near as our Sun, and as far away as some of the most distant
angry, active galactic nuclei. Wherever we have strong magnetic fields you have
particles getting accelerated. In fact, in some cases we also get what are not
cosmic rays, but they look similar. They’re cosmic ray-like things from granite
and other rocks that are embedded with radioactive materials here on the planet
Earth.

Fraser: What is a cosmic ray? Some come from the Sun, some come from deep space…
break it down for me.

Pamela: It’s basically a fast-moving, subatomic particle. You get protons, electrons and
in some cases you even get alpha particles, which are helium nuclei. If you
accelerate them at high rates, when they collide with things they expend all their
energy. If the thing they’re hitting happens to be DNA it can do damage. If it
happens to be a digital imager such as a CCD detector it creates streaks in your
image (in graduate school cosmic rays were the bane of my existence and I
learned to hate them with great vigour.

Fraser: You’re saying the word particle. That doesn’t sound to me like a ray. When I
think of a ray, I think of a piece of the electromagnetic spectrum, but it doesn’t
even fit on the spectrum, right?

Pamela: Yeah, that’s one of the weird things about this. Cosmic rays are flying particles:
they’re a single thing that gets flung at you, or the planet Earth, or something
that can detect them, at high velocities.

Fraser: So think bullets, not waves.

Pamela: They’re bullets not rays.

 

Now, I have this sneaking suspicion, and I have no way of confirming this that I
know of, that the name cosmic ray may have come from the fact that they leave
streaks on detectors. So you get one basically coming to a grinding halt across
your photo-detector, across your photo-sensitive whatever it is you’re working
with. When they come grinding to a halt, their energy creates a streak on
whatever image you’re trying to take, that looks like a ray.

Fraser: All right, so give me the origin of a cosmic ray. What kind of conditions exist
and what will happen to actually generate one of these?

Pamela: So you have a proton minding its own business happening around the universe –
perhaps in a star, perhaps somewhere else.

Fraser: Sure – lets start with the ones that come from our Sun. will you have a free-
floating proton?

Pamela: A free-floating proton is nothing more than the hydrogen atom that’s been
stripped of its electrons.

Fraser: Okay, so how did it get stripped of its electrons?

Pamela: You heat it up and it gets naked . it’s kind of cool that way.

Fraser: All right. And a star is known to heat things up – so a star can strip a proton of its
electrons so you just have a naked proton.

Pamela: So you have this naked proton wandering around in the extremely hot outer,
outer atmospheres of the stars. They get trapped in magnetic loops.

 

When you look at the Sun through and H-alpha filter, you’ll sometimes see
these loops – these different neat filamentary structures on the edges of the Sun.
you can’t see them face-on, because they get lost in the glare of the Sun. they’re
getting accelerated through these magnetic loops, and when these loops break,
we get all sorts of particles flung at our planet. When they hit, we get things like
the northern lights.

Fraser: so the magnetic loops we see on the Sun, those are almost like if you take a
magnet and put it in a bunch of iron filings, the filings will move in the shape of
the magnetic field lines that are coming out of the magnet. So those loops on the
Sun are kind of the same thing?

Pamela: They’re very similar. Another way to think of it is as an electromagnet. If you
take a wire and loop it around a piece of PVC pipe (use the thickest wire you
can find and a skinny pipe), attach it to a car battery, you can use it if you attach
and detach it quickly to fling small objects that are metal. Don’t do it with sharp
objects, but it’s fun to do with little BB’s or something in an open space. This is
a project I like to give to students.

Fraser: So in that situation you’re turning on the magnetic field and the BB or whatever
is trying to align itself into the magnetic field, and just as its about to get there
and be slowed down and pulled into its correct position, you turn off the
magnetic field and its just got the momentum to carry it along.

Pamela: In particle accelerators here on the planet Earth, like CERN which we talked
about in our show about the Large Hadron Collider, they have pulsed magnetic
fields where they’re constantly turning the magnets on and off in sequence to
drag the particles in circles around and around in these loops.

Fraser: So you’ve got these protons hanging out on the Sun, they get accelerated or they
get pulled into these magnetic field lines, and then the magnetic field lines
change and you get this snap and the particles are flung out. Is it just protons?
How fast are they going? …I just asked two questions there. Is it just protons?

Pamela: It’s not just protons. It’s protons and electrons, its even helium nuclei (alpha
particles) in some cases.

Fraser: It’s whatever was trapped in the magnetic field line when it snapped.

Pamela: It’s always ions

Fraser: Water at the end of your wet towel.

Pamela: The key is its always something that has charge. It’s going to be a light atom
because it takes a lot more energy to accelerate a heavy atom.

Fraser: Oh, because they have to have charge to be picked up by the magnetic field line
anyway.

Pamela: Exactly. So you take a charged nuclei, interact it with a magnetic field, snap the
magnetic field and off flies the charged particle, the charged ion… and you have
a cosmic ray.

 

These things vary in energy. You can get pithy little tiny ones, but you can also
get some where you have a single proton that is carrying as much energy as a
tennis ball going 50-60mph. That’s a lot of energy.

Fraser: Especially if it hits your precious DNA.

Pamela: Yeah. Imagine how much it hurts your skin if you get hit by a baseball. Imagine
instead all that energy being focused and nailing a piece of your DNA.

 

Luckily, these are itty-bitty little tiny things. They’re parts of atoms. Even
though we look like solid objects, human beings are mostly empty space –
everything is mostly empty space. Most of the time these protons will happily
sail through your entire body and not interact at all. Occasionally, damage can
occur.

Fraser: Right, but aren’t we protected by the Earth’s atmosphere?

Pamela: We’re mostly protected by the Earth’s atmosphere. The magnetosphere is
what’s doing most of the protecting. Our planet has its own magnetic field, and
when these charged particles interact with the magnetic field, in many cases
these particles get their direction changed and they veer off so we don’t get hit
by the majority of them. Some of them do make it through the magnetic field of
the Earth and hit us down here on the planet Earth. There’s actually been some
possible relationships between spikes in the number of cosmic rays hitting the
planet Earth, and the frequency of cancer.

Fraser: So when the cosmic rays hit the Earth, they don’t stream straight in – they get
stopped by the atmosphere. Could we talk about our natural defences – how is
our planet protecting us from those awful rays?

Pamela: It’s primarily our magnetic field. Just like magnetic fields can accelerate these
particles, they can decelerate them and change their direction. They can funnel
them into the Van Allen Radiation Belts.

 

Our atmosphere can help as well. When these cosmic rays hit the atmosphere,
they end up reacting with things in the atmosphere, creating Cherenkov
Radiation. We get streams of different types of particles that we can then detect
with different telescope facilities that are specially built to detect these cosmic
rays.

 

There are still some that make it through, completely unaltered, waiting to nail
my CCD when I’m trying to take high-resolution images of the cosmos.

Fraser: That’s what you talked about next. You’re using your CCD and not trying to
detect them… but what’s the method astronomers use to detect them when they
go looking for them?

Pamela: There’s a few different ways. One method you can use is you can take a large
tank of often heavy water. You can actually get muons produced when cosmic
rays hit the heavy water. We can detect these through their child particles and
the flickering of light they give off.

 

Another way that we can detect this is through the chain of particles they
produce in the atmosphere. You can have a high energy proton coming in and it
collides with a molecule in the atmosphere and gives off what are called pions
which then decay into things like muons and gamma rays and neutrinos.
Through all these different chains of events, we eventually get things we can
actually detect. There are different observatories like the Whipple Observatory.

 

There’s a new facility, the Pierre Ojet Observatory, which is actually a pair of
observatories, one in the United States and another in Argentina. They’re
working to use a whole different array of methods so they can compare how
they’re detecting cosmic rays and hopefully work to figure out where on the sky
these cosmic rays are coming from.

 

Figuring out where cosmic rays originate is actually a real problem. As they’re
flying through the cosmos, every magnetic field they interact with is going to
change their direction. Some cosmic rays we’ll never be able to figure out
where they originated.

Fraser: That’s part of the mystery. You talked about the fact that we know most of the
cosmic rays hitting the Earth are coming from the Sun. That’s not all of them –
where are the rest coming from?

Pamela: Some are coming from galactic origins. Unfortunately, the galactic ones we
have no way of figuring out where they came from. The galactic magnetic field
scrambles all of that information.

 

Based on their energies and based on the shocks we see around things like
supernova, we believe most of the galactic cosmic rays originate in supernova
blasts. Some of them though have such high energies we can’t really find
anything in our galaxy that they could be coming from. We’re still trying to find
all the origins.

Fraser: Weren’t some of the energy levels in the cosmic rays higher than physicists
thought was even possible? Wasn’t it more than was theoretically predicted by
the most extreme events anyone could imagine?

Pamela: Oh, totally.

 

So sometimes (not often, but occasionally), you get physicists that come up with
humorous names for things. The Higgs Boson is nicknamed the God Particle.

 

It’s the one we’re looking for that will give mass to everything, and we need to
know where mass comes from.

 

After finding these ultra, oh-my-god-high energy cosmic rays, they got
nicknamed the “oh my god” particles, because nothing can explain what created
these things.

 

We’re starting to get some clues. We think many of them have extragalactic
origins, so they’re travelling to meet us from other galaxies. We think it might
just be that they’re coming from super massive black holes that are angrily
feeding in the centres of galaxies. These are active galactic nuclei. It’s a family
of galaxy related to quasars.

Fraser: What might be the process that’s whipping up these particles with that much
energy?

Pamela: It’s all about the magnetic fields. Active galactic nuclei, in many cases, have
these amazing jets. They appear as radio lobes in surveys like the first NVSS
surveys done with the VLA in Mexico. You look at these images and when you
super-impose the radio images on the optical images, the optical part of the
galaxy might be 20 pixels across, down in the centre of the image. Then you get
these huge radio lobes that will go out a couple hundred pixels in either
direction.

Fraser: When you say lobes… what is a lobe?

Pamela: We call them lobes. It’s the name we gave the shape. Take ice cream cones and
attach them to the top and bottom of a spiral galaxy. At the end, have the
material coming out billow as it hits the intergalactic medium.

 

We have these jets of material in some cases very tightly wound and we can
actually see twisting and winding of the material. As the material travels away
from the galaxies, it eventually ends up colliding with the dust and gas between
galaxies and it billows out when it hits, sort of like a waterfall hitting the ground
and creating a cloud of splashing water.

Fraser: So when you see the picture from a telescope of a quasar or active galactic
nuclei, the visible part may be a small little part of the screen, but then the part
that’s actually radiating radio waves is gigantic around the galaxy, and that’s
coming from the jets that are interacting with its surroundings?

Pamela: They originate from the jets. So these quasars have powerful magnetic fields
being generated in the accretion disk of in-falling material around them. You
have this spiralling charged material driving huge magnetic fields. Sometimes,
particles get flung out the poles of the magnetic fields. This acceleration creates
the jets, and it can also help create, in this chaos of magnetic fields, these ultra

 

high-energy cosmic rays that are packing a wallop of a high school student’s
tennis ball that’s getting hit at 50-60mph.

Fraser: There’s actually some brand new research that we reported on at the AAS, where
astronomers are now calculating that many super massive black holes are
spinning at the very limits of relativity as predicted by Einstein. You can just
imagine something with hundreds of millions of times the mass of our Sun
spinning close to the speed of light.

Pamela: Yeah.

Fraser: In a disk of material and with a giant magnetic field it’s building up. You can
just imagine the forces its building up. Just like the Sun, it’s scooping up
particles in these magnetic fields and snapping them like a towel at us? Maybe.

Pamela: That’s pretty much exactly what’s going on. One of the numbers I found in
preparing for the show was that in some cases, these high energy accelerated
particles are moving so fast, at so close to the speed of light, that if one of these
high energy cosmic rays – a proton – left a supernova at the same time as a
photon and they travelled for one year, the proton, which because it has mass
can’t travel at the speed of light, will only be about 46nm behind the photon that
is travelling at the speed of light.

Fraser: That’s what I heard – that one of the important things astronomers were able to,
with their latest research they were able to see some event at a super massive
black hole in a galaxy far away, and then later, see the associated cosmic rays
from it.

Pamela: This is one of the neat, new, forefront areas of science where we’re just starting
to build the detectors, we’re just starting to figure out how to detect these things
and how to triangulate where they’re coming from, and in may cases we can’t
tell where the cosmic rays are coming from, but with our optical, radio, gamma
ray, x ray telescopes we can see that a really cool event went off and then a few
minutes later, with our cosmic ray detectors, we see this flood of cosmic rays.
So we’re using the probability alignment of “if we see this and then we see this
over and over, then they’re probably related”.

Fraser: That makes sense.

Pamela: Works for me.

Fraser: Now, what kind of an impact do cosmic rays have on spaceflight for astronauts
heading to the Moon? If humans are going to be buzzing around the solar
system in the future, are these pretty dangerous?

Pamela: Yeah. This is actually a fairly serious problem we have to figure out how to
address as we look to send men and women further and further across the solar
system. Today on the International Space Station, they actually have one part
that is much better protected than others. When there’s a solar storm, they lock
everyone in that one area because it will protect them better.

 

As we start heading out… Mars doesn’t have a magnetosphere. The Moon
doesn’t have a magnetosphere. We’re going to have to develop spacecraft that
will allow astronauts to not only survive solar storms but as they spend longer
and longer periods of time in orbit, they’re going to need to not get blasted with
too many REMs of radiation.

 

Alpha particles are one of the forms of cosmic rays. They’re also one of those
things that can cause radiation poisoning if you encounter too many of them. So
we need to protect them, and we need to worry about how long people spend in
space.

 

Anyone who’s worked in a lab with radiation knows you can experience a
certain amount of radiation before you have to start worrying about the
consequences of the radiation. All of us can get our teeth x-rayed, all of us can
go down to the granite quarry now and then. But if you live in new England,
you’ve probably done a radon test in your basement because you don’t want to
live in a house that’s filled with radon. It will eventually cause increases in
cancer rates.

Going into space is the same as building your house inside the granite quarry,
where your entire house is filled with radon.

Fraser: What kind of warning will we get? Do we have mechanisms for detecting a solar
storm coming past, and a way for the astronauts to run and hide? How much
time do they have?

Pamela: People are trying to figure out ways to do this. Luckily for the solar ones they’re
not going at the speed of light. Often we have a day or so – a few hours, to get
people prepared. It depends.

 

At last year’s AAS, or perhaps over the summer, someone was talking about
ways you can tune in to coronal mass ejections, and depending on the radio
spectrum, depending on all the different colours of light and how they come off
of the Sun, you can say, “this one is going to hit us with a blast of particles, and
this one isn’t.” that’s useful information. It allows us to do things like put
telescopes into safe mode when we know they’re in trouble.

 

Now, the problem is there are these ultra-high energy cosmic rays that are
coming from beyond the Sun that we have no way of predicting. As you get out
of the Earth’s magnetosphere, the number of those that are going to hit your
body are increasing.

Fraser: The astronauts in the space station, they’re protected because they’re within the
magnetosphere.

Pamela: In many cases yes.

Fraser: Right. But if you get out of the magnetosphere and off to the Moon or off to
Mars, then you’re on your own.

Pamela: Exactly.

Fraser: I think that’s going to be a pretty big problem, and I can imagine us having these
heavily armoured (and, I guess, heavy) spaceships trying to minimize the
radiation risks the astronauts are going to be facing. That’s just going to
increase the expense of getting things into orbit.

Pamela: Yeah, and people in the international space station are only up for a few
hundred days. Going to Mars, you’re looking at 3 years.

Fraser: Right, and it’s not like once you get to the planet you can sit there and be safe.
It’s just as dangerous down on the surface of the planet as you are in space.

Pamela: So we have to figure out how to effectively protect people, lower the risk of
cancers and mutations. One of the problems with this is it’s not necessarily the
astronauts that get the cancer, but it could also be their children. You don’t want
to say astronauts can’t have children, but we have to consider the generations of
damage we can do.

Fraser: There’s one last thing that was quite interesting. One of the writers on Universe
Today did an article, and scientists had been able to track the link between
cosmic rays and cancer rates.

Pamela: Yeah, this is what I was hinting at. There was a cycle determined using ice core
samples. It’s possible to go through and determine where and when in the past
there were increased numbers of cosmic rays. In the United States, Canada, the
UK, and Australia, we have fairly good data for who had cancer and died of
cancer in the past 100+ years. Going through this data, they were able to find
there’s basically a 28 year lag between a peak in cosmic rays and a peak in
cancer deaths.

 

They also found that when there was extremely low rates of cosmic rays, 28
years later there was extremely low rates of cancer. All because there’s a link
doesn’t mean cosmic rays are causing the cancer – it could be something else. It
could be that cosmic rays are causing something else. But there is this
relationship we’re noticing.

 

One of the ideas they put forward is you have a woman who’s pregnant. While
pregnant she gets blasted with cosmic rays. She has millions of cells – she’s’
okay. But her unborn child might be a few dozen cells at the time. When you
damage one of those few dozen cells, that damage propagates to the entire
future human being. Then that future human being has a child, and it’s that child
that ends up getting and dying of the cancer.

Fraser: Wow. So is there a Suntan lotion I can get when the cosmic rays are on the
increase? Lead, right?

Pamela: Or glass – glass in some cases can be useful.

Fraser: Glass, lead, underwater.. live in a subterranean home…

Pamela: That little room the x-ray technician goes into.

Fraser: Yeah, that should be safe.

Transcript: Globular Clusters

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Fraser Cain: This week, we’re going to study some of the most ancient objects in the entire universe: globular clusters. These relics of the early universe contain hundreds of thousands of stars held together by their mutual gravity. In fact, when I get a telescope out to show my friends and family, the great globular cluster in Hercules is one of the first things I’ll point out. It just looks like a fuzzy ball through a telescope, but in my mind I can see all the stars.
 
Let’s just talk a bit about globular clusters. What are they?

Dr. Pamela Gay: They are, at the most simplistic level, they’re collections of 10 thousand to hundreds of thousands of stars gravitationally bound together that formed in some cases 12 billion years ago. They’re out, orbiting on the edges of our galaxy, and on the edges of most of the galaxies we observe out there.

Fraser: How many are we going to find in a typical galaxy like the Milky Way?

Pamela: It’s all a function of how big the galaxy they’re attached to is. Our own galaxy seems to have well over a hundred different globular clusters. We’re finding new ones every day as satellites like the Spitzer Infrared Observatory peer through the dust and gas and are able to find new globular clusters in places we hadn’t been able to look before.
 
They basically form a spherical distribution all the way around our galaxy, orbiting in some cases in two different directions. There’s two different populations. They’re old, metal-poor, and everywhere we look. They’re the ancient stewards of our galaxy.

Fraser: Okay. When we talk about ancient, how ancient are they?

Pamela: One of the great mysteries for a long time was, we looked at them and they seemed to be older than the universe. It turned out we had miscalculated how old the universe was and we had miscalculated how old the stars were. Around the year 2000, once we got everything put together, it began to show up that our universe is 13.7 billion years old and these clusters of stars are 12 billion years old.

Fraser: I love that. I love that up until the year 2000, astronomers knew there were stars that were older than the estimates of the age of the universe, and that bugged them, but they were able to just kind of deal with it – “yeah, we have our estimate for the age of the universe wrong, and we probably have our estimate for the age of the stars wrong, but for now this is the best we can do.�
 
[laughter]
 
I think that’s great.

Pamela: I’ve had this moment at the chalkboard before. You start off at the upper-left-hand corner of three chalkboards and you start deriving equations, and you keep going and going and get to the very end and look at the number on the board and it doesn’t match the number you calculated in the quiet of the privacy of your own office. You know somewhere on those three chalkboards, there was a mistake. And you don’t know where.
 
Now, at the chalkboard, I can usually go through and my students are more than willing to help me find where I dropped the one-half or squared something that should’ve been cubed. But when making calculations of the age of globular clusters, you’re not talking about three chalkboards of calculations. You’re talking about thousands of lines of computer code going through and trying to calculate stellar evolution models, saying, “a star spends this long on the main sequence doing these things�
 
In all those thousands of lines of code, in all of the mathematics that go into the simulations to write those thousands of lines of code, there are so may places where our approximations might not be right, or where we might be missing a term in our calculations. It took us a long time to figure out what was going on and to get computers powerful enough that we didn’t have to make as many approximations.
 
Then, when it came to measuring the age of the universe, it was an observational challenge that was pretty much unsettled until the WMAP results came in. There, we just had to build the bigger, better microwave telescope.

Fraser: Okay, fine. So they’re not older than the universe. That’s still plenty old. What kind of forces came together to build these globular clusters in the first place?

Pamela: A large, dense, glob of stuff all by its lonesome settled into forming dense, rich stars. Over time, the stars segregated themselves by mass.

Fraser: Why did they form all these different stars and not just one big, supermassive black hole?

Pamela: As the cloud of material collapses, it ends up fragmenting. It turns out that you don’t generally have one nice, completely smooth cloud of gas. Rather, you have a cloud of gas with a few knots in it. Those individual knots, those individual places that are a little bit more dense than other locations, as the entire cloud collapses those little knots end up collecting gas to themselves, hogging it and forming individual stars out of this large clump of gas and dust.
 
It’s through the fragmentation that you end up with these populations of tens or hundreds of thousands of stars all clumped together.

Fraser: Do they form as separate clumps as the galaxy is forming, almost like planets inside a solar system might form around a star? Or did they form as kind of mini-galaxies and get absorbed into galaxies through collisions later on?

Pamela: One of the large mysteries we’re trying to sort out is why we have globular clusters with very specific geometries and star distributions that are roughly the same size as dwarf galaxies. What is it that made one clump of dust and gas form a globular cluster, and another clump of dust and gas form a dwarf galaxy? We’re still working to figure that out.
 
We think part of it might be globular clusters form in the halos of pre-existing giant galaxies. Dwarf spheroidal galaxies tend to form in isolation all by themselves. Some how, the kinematics involved ends up with two different things forming. Part of this might be the dark matter involved. Globular clusters don’t have the same dark matter halos associated with them that you get with little tiny dwarf galaxies. If you take a dark matter halo and throw a globular cluster’s worth of mass inside of it, you can get a dwarf galaxy.
 
If instead you just take a clump of dust and gas and embed it inside the much larger dark matter halo of a giant galaxy like the milky way, then you seem to get globular clusters.

Fraser: I didn’t realise that the amount of matter in a globular cluster could be the same amount as in a dwarf galaxy. That’s quite interesting.

Pamela: It’s one of those weird things. This is only true for the smallest of the dwarf galaxies and the largest of the globular clusters.

Fraser: What about composition? What kinds of stars are they? You called them metal-poor – why’s that?

Pamela: Stars come in a lot of different compositions. Our Sun tends to have, for a star, a lot of things like iron – a lot of heavier elements (like silicon). We can look at it’s spectrum and say, “look at all those rich titanium lines, those rich strontium lines in the spectrum of the star.�
 
Instead, if I start looking at the elements found in the stars of a globular cluster, I’ll see a lot of those elements just aren’t present. These stars can have a hundred or even a thousand less metal than our Sun has in it. We call these stars metal-poor because compared to the Sun, they have only a percent or a fraction of a percent of the same number of heavy atoms in their atmosphere.

Fraser: I know that stars get their heavier elements through successive generations of stars living, exploding as supernova, releasing their material which gets sucked into a new star-forming cloud so you get recycling going on and on. Do they just not get a chance to go through very many generations before they formed?

Pamela: 12 billion years ago, there just wasn’t that much heavy metal hanging out waiting to be eaten into the newly forming stars. One the really cool things about globular clusters is pretty much all of the stars in the globular cluster formed in one violent period of star formation.
 
When I look at a sample of a hundred different stars in say, M13 (the Hercules cluster you mentioned), all those stars are going to be basically the exact same age. They’re going to have formed out of the same cloud of material (so they have the same composition). The only thing that varies from star to star in these systems is their mass.

Fraser: That was going to be my next question. We learned early on that the heaviest stars burn their fuel quickly and then detonate at supernova, while the smaller – the Sun-sized stars and smaller can live on for billions and billions of years as main sequence or white dwarf stars. Is there some kind of mass limit where you just doesn’t see a certain size of star in those clusters anymore?

Pamela: That’s right. You look at these things and none of the large stars are left any longer. You’re down to stars smaller than the Sun hanging out on the main sequence. Then, you have remnants of the stars. You have whit dwarfs, neutron stars, all hanging out going, “hey! We used to be big!� these are stars that shed their mass, exploded as supernova and went through planetary nebula formation. Those planetary nebula have, in many cases, been largely destroyed just by the passing of time. Globular clusters are systems rich in ancient stars and stellar remnants – nothing young or big.

Fraser: Are there any forces that will take a globular cluster apart? They’ve been around for 12 billion years – there must be some really serious forces keeping them together.

Pamela: They’re one of the most tightly bound objects we know of (in terms of large populations of stars). Open clusters, in the disk of our own galaxy are much smaller – hundreds of stars in some cases. They get shredded by gravity over time. Globular clusters are tightly bound systems that are able to, in general, sustain orbiting our galaxy.
 
As we look around we do see instances of globular clusters that are elongated or a little bit mis-formed, that have gone through gravitational interactions with our galaxy or with other galaxies. That’s the cool thing: we can observe globular clusters around our galaxy, around some of the dwarf galaxies (the Fornax dwarf has its own globular clusters, we see them in the Large Magellenic Cloud). We can see them in all different environments, and in some cases the environments are rather hostile and destructive.

Fraser: Why do astronomers find globular clusters so interesting? Do they use them as a tool for some of the science they’re working on?

Pamela: They’re laboratories. Because you can look at M3 and get several thousand stars made out of the same stuff, you can see “if I change this variable involving mass, I get this difference in outcome. If I create a binary system, I get this difference in outcome� We can use them to say “I’ve now controlled for age and composition, all I’m going to vary is whether a star is in a binary or not, and what the mass of that star is.� I can then see the outcome in the star’s evolution.
 
These things, while they’re all more metal-poor than our Sun (at least the ones around our own galaxy), they’re all slightly different ages. They’re ancient – but they’re slightly different versions of ancient. It’s sort of like going from a 70 year old to a 90 year old. They’re all grandparent-age, but there are differences between a 70 year old and a 90 year old biologically. With these systems, they’re all ancient, but there are differences in stellar evolution that we’re able to observe.
 
They’re one of the most fascinating tools for studying stellar evolution that we have, because you can see so many stars and control what you’re looking at so carefully.

Fraser: I guess with a hundred thousand (or more) stars in a cluster, you can see every single mass of star from the smallest white dwarf, or the smallest red dwarf, all the way up to the largest star that hasn’t died yet. I guess you can see, in some clusters that line falling off. In some cases, the bigger stars have died, and in other clusters they’re younger and the biggest stars haven’t died yet.

Pamela: Yeah, no. All the big stars are dead. That’s the funky thing about them: there are no big stars. You’re left looking at strictly solar-sized type stars and smaller in most cases.

Fraser: Do we see any clusters that are younger than this 12 billion years old? Do we see any that are just forming anywhere?

Pamela: Not locally, but as we look out at other galaxies, we do start to be able to see them around other galaxies, particularly in star-forming regions and in areas where galaxies still have chunks of basically, virgin gas waiting to get used. We did, starting in 2000, start to discover newly-forming globular clusters. That was kind of cool. Up until then, we had no clue where these buggers came from, we just knew they were out there. We didn’t know which came first: the galaxy or the globular cluster. Now we know that they form together.

Fraser: They form together. I know there’s a relationship between supermassive black holes and galaxies themselves. Is there a relationship between globular clusters and the galaxies they live in?

Pamela: This is something we’re still trying to work and figure out. One of the problems is we can steal globular clusters from other galaxies when we eat them. It’s hard to sort out the naturally born, biological globular clusters (to use a bad analogy) and the adopted children.

Fraser: How would we tell the difference?

Pamela: That’s the problem. With the Milky Way Galaxy, we have these two populations of globular clusters. One is orbiting around the galaxy in the same direction the galaxy is rotating. The other population seems to either not be rotating relative to the Milky Way or it’s going in the wrong direction.
 
With these two different kinematic populations, we also find differences in the composition of the stars. One population has even fewer metals than the other population. Astronomers are left thinking this is probably because we ate another galaxy and stole its globular clusters, but there’s also the possibility that maybe one group of these systems just formed a little later on, a little further out. We’re not really sure.
 
We need to keep studying, and keep looking at other galaxies with high-resolution images. If I watch a galaxy that’s just starting to form (and we’re just starting to find occasional examples of galaxies still forming today), how is it the globular clusters form with them?

Fraser: There was actually a really interesting piece of research that came out in just the last couple of weeks, where scientists were using a globular cluster as a laboratory. In this case they wanted to look at the distribution of regular stars and white dwarfs. Their assumption was the stars will sink down to a certain point in the cluster, depending on their mass – the heavier stars will sink to the middle and the lighter stars would be pushed up. They found a lot of white dwarfs were higher up than they were expected to be. Did you read that?

Pamela: Yeah – that was a really neat case. With globular clusters, the stars do stratify themselves, where the really bloated bigger stars, even the really ancient red stars (the really giant ones that aren’t too much bigger than the Sun necessarily, and they aren’t main sequence stars, but they’re still bigger than little tiny baby red dwarfs). These bigger stars sink to the centre of the globular cluster, but the lighter stars end up floating to the surface. They actually pick up kicks from gravitational interactions – the bigger stars get less of a kick and the littler stars get more of a kick and are able to move outward in the system.
 
They looked at white dwarfs. White dwarfs come in a small variety of masses. They expected to find the heavier weight white dwarfs in the centre and the lighter weight white dwarfs further out. When they looked at really old white dwarfs (ones that had started to cool and weren’t quite as blue in colour), that was true: the bigger ones were further in and the lighter ones were further out. When they looked at really young white dwarfs, from stars that just finished going to the white dwarf phase, all of the young white dwarfs were on the outer edges (that they found) of these globular clusters.
 
They think what’s happening is these stars, during their last stages of life as they puff off their atmosphere, somehow this puffing off isn’t completely symmetric. Just like someone going out into space with a little air can, when you spray your air can you might end up rocketing yourself slightly in one direction. These stars, by throwing off more mass in one direction than another, are able to rocket themselves to the outer edges of the globular cluster.

Fraser: Oh I see, so when they turn into a white dwarf, it’s almost like a natural rocket. They push themselves outside the cluster and then over time, when they no longer have that kick, gravity asserts itself again and they get sorted back into where they belong in the cluster.

Pamela: In open clusters of stars in the plane of the Milky Way, this kick is enough that white dwarfs leave the open cluster behind. In the higher gravity environment of globular clusters, these stars are kind of stuck hanging out on the outskirts and don’t actually get to escape. Overtime, through various interactions with other stars, they do end up sinking to where they belong due to their mass.

Fraser: I know there’s been a revolution over the last decade or so: with a lot of the new infrared observatories they’re finding a lot of brand new star clusters, some of them are even quite close.

Pamela: As I said, globular clusters form a sphere around our galaxy. This is actually how we were originally able to figure out where in our galaxy our solar system is located. We looked out and could say, “I see this number of globular clusters in this direction, this number in this direction and I know they form a sphere.� We were able to pinpoint how far from the centre of the sphere we were located.
 
There were certain areas of the sky where we weren’t able to look through the density of stars, gas and dust in the plane of our galaxy. We weren’t able to see that population of globular clusters in that outer sphere, just because they were blocked from our view completely – just like if you threw a hula-hoop around your head, there would be sections of the area around you that you’d never be able to see.
 
With the Spitzer Space Telescope, we’re able to start peering through the gas and dust. Really long wavelengths of light (really red infrared wavelengths) are able to skirt through gas and dust like no big deal. By using this other colour that’s invisible to the eye, Spitzer is able to see through the crowded disk of the galaxy to see objects that had previously been hidden from us.

Fraser: Including clusters.

Pamela: Including clusters.

Fraser: Did that change our understanding at all about the distribution of them, or was it always suspected that they would be there and look, they found them?

Pamela: It was always suspected they would be there. This was one of those times we were able to say “Aha!� we knew what the distribution should look like. We couldn’t prove it, because there were these areas we couldn’t see in. Now, as we peer into these new areas we can say, “yep – we had it all right all along.� It’s always good to be proven right.

Fraser: What do you think the future holds for globular clusters? Will they just hang on forever, or will they just get chipped away and eventually dissipate into a galaxy?

Pamela: I think they’re going to hang on for a long time.

Fraser: Define long – we’re talking astronomical terms here, so you can use some big numbers.

Pamela: Ohhh… they’re going to be around for billions and billions of years to come. They’re going to survive the collision of Andromeda and the Milky Way and end up orbiting whatever new system we end up forming. I’m sure a few will be lost along the line, but there will be survivors out there.
 
What’s kind of cool is someday far in the future, someday these clusters of stars are going to be clusters of white dwarfs, neutron stars and the occasional peppering of black holes. We’re looking at future compact mass object clusters instead of star clusters.

Fraser: They’ve got to be the perfect place to look for black holes and neutron stars. Are many found there?

Pamela: Finding neutron stars is always hard. You end up having to look for them by looking for binary companion systems. Globular clusters are extremely dense, so it becomes hard to do the detailed observations necessary to find neutron stars.
 
We are finding black holes in these systems. They’re able to make themselves apparent by eating things now and then. As gas and dust pours into a happily feeding black hole, it gets heated up and excited into giving off x-ray light.
 
By pointing telescopes like the XMN Newton at globular clusters, we’re able to go “Ooo! X-ray emission – there must be a black hole there.� We’re finding the theorized population of intermediate-mass black holes can in some cases be found lurking in the centres of globular clusters. This is brand new information (fresh from last January).
 
We started to get hints about 10-15 years ago that there was observational, certain evidence that there are super-massive black holes in the centres of certain galaxies. We’ve looked for them in the centres of dwarf galaxies thinking we’d find smaller ones and that’s been a really hard journey.
 
It was theorized that since globular clusters have similar numbers of stars, perhaps they had intermediate-mass black holes in their centres. In the very second globular cluster they looked in (unfortunately not the first), there was that x-ray emission that said, “yes, there’s an intermediate black hole here and it’s eating something right now!�

Fraser: Good chances – that’s amazing.

Pamela: It’s always nice when the needle decides to sit on the top of the haystack.

Fraser: Yeah, exactly. There’s a classic science fiction story by Isaac Asimov, called Nightfall, where the planet happens to exist in a binary system or in a star cluster. It’s always light – it’s never dark. The astronomer predicts a bunch of the suns are going to be down and there’s going to be an eclipse and things are going to be dark… and predicts everyone’s going to go crazy.
 
I can just imagine… what would it look like to be on a planet in a cluster like that, and to see the sky? What would it look like?

Pamela: Here’s one of the random factoids that helps eliminate it (to use a bad pun).
 
Our nearest star of noticeable brightness is a little more than three light years away. There are 100 thousand or more stars crammed into 100 light years’ diameter sphere in a globular cluster.
 
From within the globular cluster, you have hundreds of stars that are amazingly bright every where you look in the sky, many of which are visible during the day as you orbit whatever star you’re able to orbit. It would be amazingly bright.
 
The only way I can imagine getting sufficient eclipses is if you’re surrounded by an asteroid cloud – and that wouldn’t be a good way to be a planet.

Fraser: Maybe it wasn’t a star cluster, maybe it was just a system with a bunch of stars, but a globular star cluster would take that to the next level.

Pamela: Yeah.
 
So there are some space artists out there who have done amazing artwork where they’ve sat down and worked with the scientists to work out what it would look like to orbit a brown dwarf, to orbit in a star cluster. There’s some amazing work out there if you just Google hard enough and look around. Lots of different folks are working on this.
 
Life in a globular cluster: it’s like if you imagine having a spaghetti colander above you with a floodlight. A hundred thousand stars near by shining down on your little world.

Fraser: I would love to see that.

Pamela: For now, these are objects that you can go out and see what they look like with a pair of binoculars and in some cases just your eyes. Omega Centauri (if you’re lucky enough to live in the right part of the planet) is bright enough to see with your naked eye. M13 is out there waiting to be discovered. All of these systems make excellent small telescope opportunities.

Fraser: I highly recommend it – if you have a small telescope or a friend with a small telescope and you can say, “show me a globular cluster!� They’ll know where to point it. It’s quite surprising – you’ll see a nice, little…. Well, it’s a fuzzy ball. But in your imagination, think about that distant world with a spaghetti strainer series of holes with floodlights above you. It’s amazing.
 
[laughter]
 
But yeah, I really like looking at the clusters. That’s one of the first ones I’ll point to, after Saturn.

Fraser Cain: This is such a cool topic: here we go. Astronomers have always searched for larger and more powerful telescopes, but the most powerful telescopes in the Universe are completely natural, turning the mass of an entire galaxy into a lens that astronomers can look through. We’re talking about gravitational lenses, which let astronomers peer back into the earliest moments of the Universe.
 
Pamela, what’s a gravitational lens?

Dr. Pamela Gay: It’s basically this really neat way that the gravity of an object (a star, galaxy or cluster of galaxies) can work just like an optical lens to bend light. In this way, they can bend light that would otherwise go off in some other direction toward the Earth and increase the total amount of light from some distant object that we’re able to see.

Fraser: What’s the underlying principle that’s bending light here?

Pamela: There’s gravity! It’s one of those things that, when you start to realise energy and mass are two sides of the exact some coin, and that light is just energy, and gravity can cause that light to be deflected, to move the same way it can cause you and I to move, it’s possible to start using mass to focus light.

Fraser: So with a gravitational lens, you’ve got light from some more distant object passing some mass like a galaxy, and that mass is warping the space around it so the light follows a different trajectory and bends.

Pamela: A good way to think of it is, if you imagine that it goes: your nose, far, far away a galaxy, and even further back than that, a quasar, light from that quasar is going to be heading off in all directions filling a sphere. Some of that light would normally not just miss your nose and go above your head but miss your nose and hit a star somewhere above your head.
 
That light that would normally have gone up above you, as it grazes over the top of that galaxy between you and the quasar, it can get bent so that its new path brings it straight to the tip of your nose.
 
This also has the neat affect that if the alignments are just right, we can see two images of the exact same object. One is the straight view, and the other is seen reflected in a mirror, the same way you can take and use a mirror to look around a corner.

Fraser: Let’s see if I understand this: you’ve got a sphere of light coming out of the quasar, and some of that light is going to be passing very close to this galaxy and what would go in a straight line gets turned in a little or turned as it gets attracted toward the galaxy and so we here on Earth, that’s far down the path, see this light converging back on us because of this warping. So that’s why we see a magnified version of what’s behind it.

Pamela: In fact, the gravity can cause a bunch of different effects. It can distort the light from a background object, this is where you get galaxies that appear as strange arcs around Abell clusters. You can also get what’s called a microlensing event, which is where a background object appears to be a great deal brighter due to an intervening mass.
 
You can also get neat affects such as double quasars, quadruple quasars, Einsteinian rings, where the light from a background object is multiplied into multiple images or twisted into a ring where there once was just a single point-like object.

Fraser: You say these are wonderful things to look at, but wouldn’t a telescope manufacturer be trying to grind the mistakes out of the mirror? If they saw this kind of stuff?

Pamela: In a real telescope, you really don’t want your telescope to produce fun house images. The reality is that looking at galaxies through gravitational lenses is sometimes just as distorting as if you look through the old deformed glass in extremely old houses, or if you are looking at yourself reflected in a carnival glass. But, we’re allowed to see things we can’t otherwise see, and sometimes the stuff that we’re seeing is invisible stuff, like when the gravitational lenses are made out of dark matter.

Fraser: So I guess the astronomers are going to take what they can get. They don’t have a telescope that powerful, so the fact that there’s one naturally out there that does provide a bit of a distorted image but still allows you to look much further back… how much further back can they see?

Pamela: The very most distant galaxy that has ever been detected was found using an Abell cluster to gravitationally lens a background galaxy.

Fraser: So this is an Abell cluster, an intervening cluster of galaxies where it was able to focus the light from this more distant galaxy.

Pamela: In this case it was Abell 2218, and back in 2004 they were able to get a redshift to measure the recession rate of a smear of light that they were able to detect because it was being magnified, it was being lensed by the gravity of this giant cluster of galaxies.

Fraser: So theoretically, how far back could astronomers push this technique?

Pamela: It’s all a matter of how good are we at taking a spectra of a smear of light. If the alignments are right, you can perhaps get multiple galaxy clusters that are gravitationally lensing an object multiple times that, with all of this combined lensing, allows us to look back to objects (that we currently can’t see using existing telescopes) that were formed at the very edge of the Universe in the moments right after the Cosmic Microwave Background was formed. We haven’t found those things yet, but the potential is there, as we look at the smears of light.

Fraser: I guess with a more powerful telescope or with a luckier alignment of foreground object and background object, we might find some of those first objects.

Pamela: We’re also finding objects within our own galaxy (that we can’t find any other way) using gravitational lensing. There was actually a planet, it had a truly terrible name: OGLE 2005-BLG390 (that’s the parent star). It has a planet going around it that we found because the star and the planet gravitationally microlensed a background object and we were able to see the mass of both the star and the planet as the background star was lensed.

Fraser: So we’re just talking about a star here, not a galaxy. This was two stars lining up in our Milky Way and we happened to be in the exact right spot to see the line up.

Pamela: What’s neat in this case is as you have the foreground star passing in front of a background object, we can’t see that star. This was a little red dwarf, too far away for us to be able to see with our telescopes because it just doesn’t give off a lot of light. As it orbited in front of a background object, the background object was something bright enough we can see it every day.
 
That background object suddenly increased in brightness in a away that isn’t characteristic of a nova or a flare event or any other normal brightening. It increased in brightness in a perfectly symmetrical way that indicated that an object was passing in front of it and then moving out from in front of it at a constant velocity.
 
In the process of doing this, there was a little blip on the side of that increase and decrease in brightness. That blip corresponded to the planet getting in on the act of microlensing the background light. We were able to find what we think was a rock or an icy planet (one of the smaller mass planets that have been discovered), because of this microlensing event.

Fraser: This is a once in a lifetime opportunity, to see this star and its planet, because you need that line-up, so unless it lines up with another star that we know of, we’ll never see it again.

Pamela: This was a roughly 13-Earth mass planet that we have a observation of, and we have a observation of its star, but still it’s cool!

Fraser: Right, but there’s no chance for follow up observations.

Pamela: Not with current technologies. This is where you wait for the OWL telescopes and the other freakishly large telescopes astronomers are planning to build.

Fraser: I recall it was quite far away, it was like tens of thousands of light years away.

Pamela: It was a star out on the edge of our galaxy, but it’s a new way to get at data in places that we otherwise can’t observe.

Fraser: What’s the process for this the, are astronomers watching stars to see them brighten like that?

Pamela: There are two different projects: OGLE and MACHO. These two programs are regularly looking at certain areas of the sky night after night after night waiting for microlensing events. What they do is take picture after picture of the same region, and as they take these pictures they subtract them off of a previous night’s images and look to see what is different.
 
In the process of finding these differences, sometimes they’re actually discovering variable stars like the Cepheids and RR Lyraes that I like to study. Sometimes they’re finding nova, sometimes they’re actually finding things like supernova light echoes that are moving through these regions of space. Really cool science.
 
They’re also (unfortunately at lower events) finding microlensing events. They’re finding lots and lots of RR Lyrae stars, lots and lots of other variable stars. Occasionally, out of the noise, they find these microlensing events that indicate there’s a dark object (a white dwarf, a brown or red dwarf, a neutron star, something that we otherwise can’t see) out in the outskirts of our galaxy, plugging along occasionally lensing light from perhaps the Large Magellenic Cloud stars, perhaps background objects. It’s these lensing events that are allowing us to get a sense of how much of the dark matter in the galaxy is made up of perfectly normal stuff that we just otherwise can’t see.
 
All the dark matter in the galaxy could be accounted for if there was roughly one ACME brick per solar system volume of space. If that were true, we wouldn’t be able to see out of the galaxy really well. It’s important to find the actual ACME bricks that are out there (which tend to be shaped more like brown dwarfs) and this is one way of doing that.

Fraser: Now, earlier you talked about how the larger gravitational lensing is helping astronomers map dark matter distribution. Can you go into that in some more detail?

Pamela: There was actually a really, really neat Hubble result that just came out. If you haven’t read about it yet, go over and look at our friend the Bad Astronomer’s website. Hubble basically found a smoke ring of dark matter around a galaxy cluster, CL0024+1652.
 
What they do is, they look at background objects. They assume in this little tiny region on the sky, I have 100 background galaxies. These galaxies are going to have random orientations, random shapes. If I average together all these galaxies’ shapes, they should average out to perfect little circles on the sky. But, if there’s matter between me and those background galaxies, that matter is going to cause all of them to be systematically twisted a little bit, the same way as if all of them were reflected in the same carnival house mirror.
 
So we look for those slight twists, those slight ellipticities, the slight teardrop shapes that crop up in the background galaxies. When we find these irregularities in their shape, the deviations from being little tiny circles, then we know there’s dark matter and we can map the distribution of the dark matter by reverse engineering what was necessary to make these galaxies not average out to a little disk.

Fraser: So in this case, we don’t have a galaxy in front of another galaxy, we have this invisible dark matter that’s acting as this gravitational lens, distorting the image from the background galaxy.

Pamela: What’s really cool is this dark matter is forming a donut (one of my favourite shapes apparently) around the cluster of visible galaxies. This is the type of thing that can happen when there’s a collision between two systems. You shock the system, one passes through the other and you end up with a ring of material. We’ve seen this in individual galaxies before and after collisions, but now we’re seeing it in an entire cluster and it’s not just the material of the cluster, it’s the dark matter itself that forms the donut. That’s just really cool. We’re not used to thinking of dark matter as actually forming structures,(at least not forming structures on this type of scale), and it’s a really neat, really hard to do discovery.
 
Every day we’re learning more about the distribution of dark matter. Back in January, after the AAS, we actually reported here on this show about the COSMOS project, and how they’d mapped out the large scale structure of the Universe to find that the structures of the luminous matter generally fell within the structures of dark matter, but didn’t necessarily have precisely the same centres.

Fraser: So I guess this was the same technique: they looked everywhere, looking for that distortion, and then carefully mapped it back to figure out where all the dark matter was.

Pamela: They mapped a fairly significant area on the sky, and they built a 3-D model of dark matter using gravitational lensing of galaxies at various distances away from us. Again, really hard to do, really good, solid science. We don’t know what dark matter is, but every day we’re getting a better and better map of where it is.
 
We can also use dark matter to sometimes get to repeat our ability to observe specific events. There are quasars out there that have been gravitationally lensed in such a way that when you’re looking at the sky, you see two identical objects that are separated by a few arc seconds to more than a few arc seconds on the sky. This means that you can go out, look directly at the quasar or you can look at the lensed version of the quasar.
 
The first one of these was actually given the name, Old Faithful (or scientifically, Q0957+561).

Fraser: I like “Old Faithful”

Pamela: Yeah, I like “Old Faithful” too.
 
[laughter]
 
We can’t name things well in astronomy. I admit to this fully.

Fraser: There’s too many objects.

Pamela: Yeah, yeah it’s kind of hopeless. But what’s cool about this object is you have two quasars that are far enough apart that any good telescope can clearly resolve them. The two light paths, the one to look directly at the quasar, and the one to look at the gravitationally lensed quasar (where the light has already started to head off somewhere else and then deviates and comes back to us), it’s a difference of over a year.
 
So if you catch the tail end of the quasar doing something cool (and quasars actually flicker and do neat things on short time-scales indicating stuff going on with the supermassive hole in the centre), if you only catch the tail end of an event, you just go back a year later and watch it occur in the lensed version of the quasar.

Fraser: Wow!

Pamela: You don’t get to repeat observations very often. This is like the only way you can get to get a second try at getting your data.

Fraser: It’s like a TiVo for the Universe
 
[laughter]

Pamela: Exactly, it just requires the mass to be in just the right place.

Fraser: That’s amazing. Are there any other places where gravitational lenses come into astronomy?

Pamela: The primary neat places for them are: looking at these quasars where you get multiple images; mapping dark matter; using them to zoom in on objects at high redshifts and using them to zoom in on little objects (well, not zoom in… using them to detect little tiny objects) in the outer part of the galaxy. These are the main directions, but then there’s also some nifty science that comes out of this just in terms of using theory to do funny things.
 
There was a scientist down the hallway from me at the University of Texas. Hugo, Hugo Martel. Great Canadian from Quebec. He figured out what distribution of matter would be required to create a lensed image that looked like a smiley face. It’s just a great abuse of science, but that’s the neat thing: you can take a perfectly normal quasar, with a perfectly normal, nice, happy, “I’m a disk” light and twist its light with intervening matter in ways that you can create arcs, in ways you can create smiley faces and all sorts of other neat patterns.
 
In the process of figuring out what distribution of mass is necessary to make a smiley face, he was able to also figure out what is needed to reverse engineer the distribution of mass between here and there so that when we do find these things that look like waves on the ocean, when we find these things that look like a three-year-old’s version of drawing a seagull, we know what mass is required to get to that observed image.

Fraser: I guess that was my question, as you said earlier on, when astronomers look through telescopes they see these distortions, these fun house mirror images, which in some cases is great because you get a chance to see something and not nothing, but are there techniques to try and reverse engineer the light to try and get a better sense of what the object is? Could there be a day either now or in the future when astronomers can use these lenses and actually rebuild a spiral galaxy image as opposed to a smear around the outside of a galaxy?

Pamela: We’re already there, at a certain level. Just as we had to figure out how to build a corrector for the Hubble Space Telescope based on the observed distortions in the early images, we have also figured out how to mathematically figure out how to get back at the original shape of these distorted galaxies.
 
What they do is say, “we have these 100+ galaxies that should average out to a nice polite circle on the sky. They don’t.” and then they do the trials. They do the simulations, to figure out where do I need to stick mass in the volume of space between me and these galaxies, to get the perhaps teardrop shape. Once you’ve figured that out, you can reverse engineer the path of the light to get at the original shape. It’s really cool to look at some of these simulations.
 
With the COSMOS team, they can actually trace the pathway for a beam of light that gets lensed multiple times as it passes from high redshift galaxies to the modern epic. You can see it get bent over and over as it zigs and zags, getting bent by multiple intervening blobs of mass. It’s a maze out there, and the light is forced to run this gauntlet of material because gravity bends light.

Fraser: Now does this technique work across the entire spectrum, does it work from radio waves all the way to gamma rays?

Pamela: Gravity bends everything. There are people, in fact, out there looking to see how gravitational lensing affects our views of the Cosmic Microwave Background. So we’re looking at this in microwaves, we’re looking at this in optical light and infra red light. We’re looking across all the spectrum, trying to understand what is it that we can use this really great artifact of mass and energy being the same thing, to figure out about our Universe.

Fraser: Now there’s one piece of terminology I wanted to talk about. I’ve done a couple stories on this, which are called Einstein rings.

Pamela: Yes.

Fraser: I know they have to do with gravitational lenses. Can you explain what those are?

Pamela: This is the neat situation where you get a perfect alignment between us and a distant galaxy or let’s use a quasar (because quasars are neat little point sources).

Fraser: And quasars are the actively feeding supermassive black holes at the hearts of galaxies, right?

Pamela: Yes, exactly.

Fraser: pouring out tonnes of energy.

Pamela: So you basically have the very centre part of a galaxy pouring out gobs and gobs of light such that an active galaxy that is billions of light years away – so far away that the disc of the galaxy is extremely hard to observe with the largest telescopes – the very centre, the active part, is just the brightness of a normal, faint star. They’re really powerful, fascinating things.
 
Now, if you take one of these (and they exist in the largest numbers in the early parts of the Universe, when there was just more stuff for central supermassive black holes to be eating). If you look at one of these in the distant Universe and plot a concentration of mass exactly on the line of sight between us and them (so it’s a perfect, straight line: our telescope, the lensing object, the background quasar). The lensing object is going to block the light that’s trying to get straight at us from what’s being lensed, but the light that’s trying to go above, below, left, right, diagonals… the light that’s trying to go in a perfect ring off in other directions away from us, all that light is going to get bent toward us. If it doesn’t make it all the way into focus, if it doesn’t make it all the way down to a single point before it reaches us, we’ll see that light that’s getting bent as a ring.

Fraser: Is this a temporary situation, will this Einstein ring last for years or could we be anywhere inside the Milky Way and still see it?

Pamela: This type of gravitational lens, made up of quasars at large redshifts and galaxy clusters (or other large-mass objects) at moderate redshift distances, here… human life-scales, not seeing any motion going on. But on cosmic timescales, everything in the Universe is in motion, everything changes, some day those particular Einsteinian rings are going to lose their alignment, but other ones will step forward to take their place.

Fraser: And being an astronomer focussed on this is all about being at the right place at the right time.

Pamela: Well, the whole concept that we’re never really at the exact right place at the right time… this type of thing is always out there, we’re just at the right time for this one particular Einstein ring.

Fraser: Right. Great, I think that covers the concept. I think, astronomers who need to go bigger are just going to have to go out and find themselves a galaxy cluster to look through.
[laughter]
 

Pamela: Sounds like a plan.