Astronomy Cast » Meetings http://www.astronomycast.com Take a weekly facts-based journey through the cosmos with Astronomy Cast. Mon, 15 Mar 2010 19:33:33 +0000 http://wordpress.org/?v=2.9.1 en hourly 1 Ep. 80: Craters http://www.astronomycast.com/astronomy/ep-80-craters/ http://www.astronomycast.com/astronomy/ep-80-craters/#comments Mon, 17 Mar 2008 23:12:35 +0000 Astronomy Cast http://www.astronomycast.com/astronomy/ep-80-craters/ Episode 80: Craters (16.3MB)]]> Southward looking oblique view of Mare Imbrium and Copernicus crater on the Moon.
Pamela's attending the 39th Lunar and Planetary Sciences Conference, and you know what that means: the Moon… and planets! When you think of the Moon, you think of craters. In fact, that's a big theme this week at the conference, so Pamela took it as inspiration. Here you go, the week we drove the show into a crater. Wait… there's got to be a better way to describe this.

Episode 80: Craters (16.3MB)
Types of meteorites:

  • Iron
  • Stony
  • Stony-Iron
  • Chondrites — these rocky meteorites do actually hit the ground frequently, as about 80-90% of meteorites found on Earth are chondrites.  The chances of reaching the ground intact are lower for a chondritic asteroid than an iron-nickel of a small size, but a sufficiently large enough chondrite will easily reach the surface of Earth intact.  And as for bodies without atmospheres, there's no difference.
  • Arizona State University site on meteorites

Parts of a crater:

All About Craters

Books:

Transcript

Download the Transcript

Astronomy Cast Episode 80:

Craters

Fraser Cain: Welcome to Astronomy Cast our weekly fact-based journey through the

cosmos. Pamela is in Houston, Texas.

Dr. Pamela Gay: Fraser, it's been a sad conference without you here with us.

Fraser: There you go but someone's got to hold the fort down back in Vancouver.

Pamela: Keeping Canada safe.

Fraser: Right, from space. But how's the conference been going?

Pamela: My brain is full. It's been an amazing week of all sorts of content. My

background is astrophysics, it's not geophysics and I have learned more in the

past week than I think I've read reading journal articles in the past several

months. It's just been an amazing experience of well science concentrate.

Fraser: Can you talk the planetary lingo now?

Pamela: No. But I at least know what the people who can speak the lingo are saying

most of the time.

Fraser: So you're able to translate a little better. That's good. Now the results of all your

work is being posted to astronomycast.com/live

We have pictures and audio and text and video, interviews, and all kinds of stuff

so if you haven't already, go to astronomycast.com/live which is where all of

the coverage for this event is.

Pamela: And it's not just me. We had help from Emily Lakdawalla of the Planetary

Society; Rebecca Bemrose-Fetter our producer has been doing a lot of blogging

and photography. We also got a special guest correspondent.

One of my students, Scott Miller, went to see STS-123. He went to see the last

night launch of the shuttle program and we have his Geeks Pilgrimage

documented over on astronomycast.com/live.

Fraser: Awesome. I saw some video of the launch and I really want to see that. Have

to see that launch before it stops launching. Let's get on with the show.

As you know, Pamela is attending the 39th Lunar and Planetary Sciences

Conference in Houston, Texas. That means the moon and planets. When you

think of the moon, you think of craters.

In fact a big theme this week at the planet is craters. Pamela has taken it as an

inspiration so this week is the week we drive the show into the crater. Pamela,

why don't you give us the basic explanation of how we get a crater. Although I

think we can kinda guess.

Pamela: Well you start with a rock, although rocks have more words than I ever knew

existed. You can have a rock that is from the moon or Mars or you can an

asteroid and these can have all sorts of different names.

Most typically the ones that end up hitting planets they were calling chondrites.

You get iron meteors that hit planets. When they impact they can come in at all

sorts of different angles. The angle of impacts affects what direction the ejecta

travels. This is the cloud of material that gets thrown out of the ground and

spewed in different directions.

But you always get a round crater. That's one of the cool things that you can

knock a planet and you can do it from all sorts of crazy angles and the crater is

always going to be a nice happy little perfect circle.

Fraser: Why?

Pamela: It's just the way the physics works.

Fraser: Right, like the rock just gets consumed when it strikes the ground and it's

always in a circle?

Pamela: There are a lot of really complicated processes that go into this. There's

conservation of energy; conservation of momentum. You hit downward and

material gets flung upwards as the energy is being released. It just ends up

leading to this nice happy little perfectly round crater.

You can get craters that end up with multiple rings of material around them. You

end up with craters that have neat layers layered through them with all sorts of

different morphologies depending on where you hit.

In some cases you can actually create an instant lake if you hit someplace on the

planet Earth and the crater happens to break through to the water table. This

actually happened last September. In Peru there is a crater formed about 15

meters across when a fairly good-sized rocky asteroid in this case, which we

didn't think those could actually reach the ground, which is a bit troubling.

But, a rocky asteroid came crashing through our atmosphere. People saw it

while they were hanging out on the roof of a hotel looking up when the asteroid

turned meteor turned meteorite hit the side of a riverbank. It poked through to

the water table and within minutes this crater turned into a little tiny watering

hole.

3

Fraser: Wasn't it making people sick?

Pamela: That was actually one of the stories that were in the news. Several different

teams of scientists a few weeks and a few months later went down to study it.

They interviewed the people involved, took pictures, documented everything.

It appears that it was a psychosomatic reaction. There was a lot of fear when

this happened that it was actually a missile from a neighboring country or just

some other country that for whatever reason decided to throw a missile at the

middle of Peru.

This was a fairly remote area near the Bolivia border and somewhat near Lake

Titicaca. There was a lot of fear and paranoia and no it was just a rock.

Fraser: Why don't you walk me through the steps nice and slow like for as a rock

strikes the ground – space to crater.

Pamela: Okay. The most typical case is you have what starts as an iron asteroid. A

happy little friendly object on an orbit around the sun minding its own business,

but its orbit happens to intersect the orbit the Earth. It can intersect it at all

different angles.

You can end up with an asteroid that hits our atmosphere head on where its path

is going straight from space straight down towards the earth. That's kind of

rare. Most of the time you're at some crazy angle.

Just probability says that its' more likely you're going to be somewhere

between zero and 90 degrees than at 90 degrees when you hit the atmosphere.

Depending on the angle that it hits the atmosphere it's going to deal with

differing amounts of slowing down from the atmosphere.

Different frictional effects as it passes through the atmosphere will slow it down,

heat it up, dissipate some of its energy and dissipate some of its mass through

all sorts of different burning up processes. This is what you see when you look

up in the sky and see this really bright streaking object. It is melting,

evaporating, ionizing all these things depending on its composition.

So it's getting smaller and smaller and so you might start off with something

that is several meters in size that ends up the size of a football by the time it hits

the surface of the earth. Then when it hits all that energy is transferred into the

ground.

You can end up with instantaneous melting. You can end up with shocks, but

the basic result is you end up with this great big splash of materials that shoot

straight up.

4

Fraser: Does the asteroid always hit? Can't they explode in the air?

Pamela: No. It doesn't. They can explode in the air, or they can vaporize in the air. The

vast majority of stuff in the air that hits our atmosphere is pebble and dust grain

size. Things like that aren't going to make it to the surface of the earth. It's

only the larger objects and how large is required really depends on the angle

that the object impacts on our atmosphere and the difference in velocity

between them.

You can imagine that you have this asteroid that is on an orbit that causes it to

just hit our atmosphere and is going just fast enough that it is mostly gravity

sucking it in. You could also end up with an asteroid that is perhaps going

around the sun in the opposite direction so it could hit the Earth's atmosphere

with the exact same angle.

Because of the difference in its' orbital velocity and our orbital velocity where

we have basically a head-on collision, it's screaming in at tens of kilometers per

second and this huge extra velocity ends up making it a much more dangerous

object.

Fraser: Okay so the rock has transferred its energy to the ground. What happens to the

ground?

Pamela: It depends on how big the object is. There are some really cool models that

have been done at Los Alamos National Lab where they have a super

computing facility. In some of these models, there are simulated scenarios of

large object hits the ocean and the splash of the ocean water is so great that a

column of water goes through our atmosphere.

So we're actually if we get hit by something large enough and hopefully this

would never happen because the tidal waves would be devastating and as would

many other things. If you hit our oceans just right, you can splash ocean water

into orbit basically. That's just really cool.

You can do the same thing if you hit land but it would be much more

devastating. This is actually how we end up getting Mars rock hitting the Earth

as meteors and being found as meteorites all over the planet.

At some point in Mars past it was hit by something big and chunks of Mars was

sent into space on orbits that carried them to Earth where they passed through

our atmosphere, survived and landed somewhere on the planet just waiting for

some geophysicist or some farmer to find it.

5

Anyone can find a meteor. They are all over the planet. They are easiest to find

in deserts and in Antarctica. But you could find one in your back yard if you're

lucky.

Fraser: Now either you're on a tangent or you're avoiding my question. I think you're

on a tangent.

Pamela: It's also after midnight where I am and also very late where Fraser is.

Okay, so the rock hits the planet and you can get dirt or water thrown into the

air depending on where it hits. The energy as it propagates through the soil can

take a chunk of the soil and actually flip it over.

You can end up with inverted layers stacked up on top the soil, dirt, or glacier

around wherever the impact occurs.

Fraser: You mean like dinosaurs on top, then newer rock, then finally topsoil?

Pamela: That's exactly what happens, it's a complete flip. If there is enough energy, it

can liquefy as it hits. Soil is made up of silicates, organic materials, because we

have earthworms here on our planet. Organic materials form just about

everywhere but they don't always have earthworms and microbes in them.

An organic material is just something that has carbon atoms and molecules. But

you take this stuff and if it has silicate in it that basically melts to glass, which is

cool and you can melt it and get these fascinating structures around it.

There is also all of the material that is in the meteor that has now turned

meteorite and that can shatter on impact and you end up with ejecta fields that

are filled with quartz crystals. You can end up with all these various blobs of

shiny glass strewn all around where the central crater is located.

You also get the pieces of the meteor if it chooses to shatter, which can be

chunks of metals. So you have this ejecta field around a crater rim that includes

inverted materials.

In some cases depending on what you hit, if you're hitting something that's rich

in metals, you might actually in the process be able to whack them hard enough

or melt them just right that you end up creating magnetic fields within the

materials that you've just knocked really hard

Fraser: All right, I know that if you hit a piece of iron really hard you can give it a

temporary magnetic field, right? Because you are aligning all the little jiggled

up iron atoms so that they're all pointing in essentially the same way and they

get that magnetic field going. So a large enough rock can do that to dirt and to

iron ore in the ground?

6

Pamela: Exactly. This is actually something that we think has happened in some cases

on the moon. If you look at the lunar craters there are some amazing maps of

the moon's magnetic fields from the lunar Prospector.

When you look at these maps, there is a little bit more magnetic field in one

place than another and is coincident with the centers of craters where there is

little upwellings of material which sometimes happens for reasons that we're

still trying to figure out.

It is thought that these magnet fields are either induced through shock, like

hitting it as you would hit a nail with a hammer, which is something anyone can

try. Go get a real metal nail and whack it a few times with a hammer really

hard and you can use it to pick up paper clips.

Either that or perhaps in some really ancient cases there was an intrinsic

magnetic field around and by heating the material, you randomize the atoms in

it if it is material capable of becoming a magnet.

As those heated up atoms cool they align along any magnetic field that happens

to be around. This is why in different parts of the planet Earth we can actually

figure out the history of the Earth's magnetic field by looking at the way the

magnets are aligned, natural ferromagnetic materials.

With the moon we have these neat little lumps and bumps of magnetic fields

that are coincident with craters. And that's just cool.

Fraser: Right, you get some lava that pours out of the ground or is created in an asteroid

strike and it is liquid enough that all of its atoms can align while it is cooling in

the magnetic field.

Then the magnetic field is cooled and they are locked in place and maintain a

record of the magnetic field that was there at the time.

Pamela: In some cases if you whack something hard enough with an object that is large

enough you can even do things like create the Earth's moon.

Our planet once upon a time was hit by another object and we go into this in our

"How the Moon was Created" episode.

Fraser: That's like a big crater there, mighty big.

Pamela: Actually, it's more like an ejecta. So the splash of material I told you about can

sometimes make it up through the atmosphere, that would be our moon.

Fraser: A really big collision.

7

Pamela: It's a really big collision. But in these really big collisions you don't always get

moons. In fact, it looks like both Mercury and Mars have giant basins. In

Mars' case one that is about half the planet – the whole hemisphere.

Both Mercury and Mars appear to have been clobbered by something of double

digit percentages of their own size at some point in their past. This had huge

morphological affects on the entire planet.

Fraser: Now what good have craters done for us?

Pamela: Well, they probably got rid of the dinosaurs which some would argue allowed

mammals to evolve on the planet Earth and thus reign supreme and destroy the

planet in new and interesting ways.

At the same time, it's a way of distributing material around the solar system and

there also a tool that geophysicists can uses to measure the ages of other objects.

For instance on the moon you can look around and there are lava fields on the

moon. The moon actually had a much more liquid core in its past and lava was

able to escape through various different types of dyke features.

There are also all sorts of very neat little underground effects of lava going

underground where we could see it and creating neat geographical formations.

We can date different features on the moon such as the highlands, the mare

based on how many craters there are in different areas. We could also measure

the depth of lava using the craters.

The way this works is you look at an area and count how many craters there are

in different areas and we can also measure the depth of lava using craters. The

way this works is you look at an area and count how many craters of different

sizes there are within that area.

You can make a plot of number of craters versus size of craters and you'll end

up with a bazillion little tiny craters and very, very few giant craters and you

can fit a pretty much straight line to those relationships.

Now in an area that has a ton of craters, where you end up with the entire line

shifted so that it intersects the Y-axis is really high number. That is a really old

surface, one that has been around for along time getting whacked with rocks

from space.

Fraser: So you just count the number and the size of craters in some region and then you

consult some geophysicists chart somewhere and it tells you how old that region

is. I guess you might have regions that are right at almost the beginning of the

solar system while other places might just be a few million years old.

8

Pamela: They actually define different geological periods based on the crater number.

This gives us the relative age. Trying to get at the actual age of a planet, a

moon, whatever requires you to actually go out, grab a rock and do radioisotope

counting. Look at what different elements have had a chance to decay in that

particular rock.

We can't do that with Mars yet. But we sent Apollo astronauts to the moon and

they landed in different places. By taking those rocks and looking at the

radioisotopes in them and what has decayed and what is left, we're able to say

this part of the moon has this age; this part another age; and use that to scale our

understanding, at least with the moon, this crater rate corresponds to this date in

the past. That's kinda cool.

With Mars, we're not at a point yet where we can do the radioisotope work and

say we know exactly how old this part of the surface is. Although we have

some fair guesses based on our understanding and on the Rovers we have sent

there so far.

However, with Mars we do the same thing. We age different surfaces and also

age things like stream beds, filuvial systems cut out by liquid we think and they

look like deltas and we're able to say this section is older or younger than this

other section based on how craters are layered on top of or not layered on top of

based on these filuvial systems.

Fraser: Now we look in the sky and we see the moon just wracked by craters and yet

here on Earth, I think there are meteor crater for well-known crater? Why isn't

the Earth as hammered as the moon?

Pamela: It rains. We are hammered just as much as the moon. The difference is that as

you look at the surface of the Earth you're not seeing any rocks that are 3.5

billion years old unless it's a rock you happen to find and pick up and test and

just happened to survive.

There are a few places on the Earth where we find old rocks but it's not the

whole surface of the planet. When we look at Mars; when we look at the moon,

we're looking at surfaces that have rocks on their surfaces that are billions of

years old and they haven't been eroded by rain or dust and the plate tectonics on

both the moon & Mars are much less.

Mars has the Tharsis Bulge, it has Olympus Mons, it has all these volcanoes that

are problematic. They raised a whole chunk of the surface. To understand

those parts of the surface we have to do all sorts of crazy other stuff. In general

the surface of both of these worlds haven't been rained on.

Already with the crater that recently formed just last September in Peru, 15-

meter diameter crater is almost gone. It rains, and the rain washes soil in,

9

flattens things back out. Anyone who has ever dug a hole in their back yard

knows the hole is going to fill itself back in rather quickly.

Our planet erodes. It kinda sucks.

Fraser: So you just wonder how many enormous craters are just gone.

Pamela: There is actually thought that things like the Yucatan are crater edges. As we

look more and more at satellite images we're finding more and more giant

craters from their rims all over the planet.

Fraser: That's right, there's like the latest satellite missions are able to measure the

contours of the Earth such precision that they are able to find these enormous

craters just by the tiny little difference in the height of the rim.

It's been eroding for a hundred million years but there is still just enough of the

rim remaining that they would know there was a crater there, that there was a

huge collision there. Only just now they are able to discover these craters.

Pamela: The other way that we're finding it is using gravity measurements. This is one

of the coolest things. I learned about this a few years ago. I thought this was

really cool and I don't geek out too much about gravity.

There is the ability to measure gravity with some instruments so precisely that

you can tell the difference in gravitational acceleration between someone's foot

and their head using this instrumentation.

It's possible to go around with gravity detectors and if you know your distance

from the center of the planet, which you can get from GPS systems, and you

measure the acceleration of gravity at that altitude from the center of the planet,

you can roughly figure out the amount of material that has to be between you

and the center to cause that acceleration. Doing this, they go out and find things

like petroleum reserves.

But working in South America, a group of geophysicists actually found a big

impact basin this way because the densities versus shape of the terrain just

didn't make sense for any other process. Gravity allowed them to find a hidden

crater.

Fraser: They're using that technique to measure ice loss from glaciers to see how the

ground such as in Canada is bouncing back after the last Ice Age. They can

measure how the ground is moving back up after the Ice Age. It's pretty

amazing.

Pamela: It was actually using these gravity measurements that we've recently been able

to figure out that the reason that you get this weird dichotomy between the

10

northern and southern hemispheres of Mars is because Mars got whacked by a

really big object. We didn't know about what had happened for a long time

because of the volcanic system that spews volcanic material all over the

boundary between the highlands and the lowlands. We had to figure out how

does that boundary move beneath the lava flows.

A group of geophysicists combined topographical maps that show the altitude

of the terrain with gravity maps that were extremely precise. They were able to

determine that if we assume that the crust of Mars has this density and the lava

flows have this density, what do the boundaries between these have to look like

in order to get the gravity we observe and the altitude of the land that we

observe.

When they did this, they could basically peel off all the volcanoes and see what

the crust looked like beneath them. They were able to find that the boundary

between the highlands and the lowlands is basically a perfect ellipse around

Mars. You pretty much can only get that shape if you whack Mars and you

make an impact basin.

There are ways that you can work really hard with other models and twist

parameters and other things and jump through lots of hoops and ignore

Ockham's razor and get this to happen other ways. But the easiest way to

explain those results is to say that Mars got whacked with something over 2,000

kilometers in diameter and didn't end up producing a moon in the process but

instead created this dichotomy between the highlands and lowlands.

Fraser: Wow, so a couple more things. One was just to talk a bit about how the gravity

and structure of what gets hit changes the nature of the crater itself.

Pamela: It's not just the gravity, it's also the surface that's getting hit. So if you impact

on top of a bunch of ices and say you dig up the soil beneath the ices and spread

them out on the top of the ice.

Then you can get these really neat plateau craters where over time the ice

around the crater in this ejecta blanket might vaporize or sublimate away and as

this ice goes straight to gas where the soil has been dug up and plopped down

onto the ice it can't do that. You end up with that layer of ice basically

protected by the ejecta that's on top of it and everything else around it gets

lower and lower and vaporizes into the atmosphere.

You also have depending on the gravity the amount of stuff that gets flown up is

going to differ. If you hit a really big heavy object with a rock, the gravity of

that object is going to hold on to the material and make it not fly out quite so

much.

11

But if you hit something much smaller you launch rocks from Mars to Earth.

So the height of the crater walls is going to be a function of the density of the

material you're hitting and the gravity of whatever it is that you're hitting. It all

plays together.

Fraser: I know we mentioned when we were doing our tour through the solar system

some of the bizarre crater formations in some of Saturn's moons.

Pamela: The death star.

Fraser: Yeah, where it almost looks like it's hitting a real spongy material and the

material is just collapsing. I think there's one last really good use for craters

that we haven't talked about which is when the astronauts return back to the

moon one of the things that they will be looking at is the craters at the southern

pole of the moon which are in some cases eternally in sunlight and in other

cases eternally in shadow and may even hold water ice.

Pamela: One of the things that is amazing that I just learned this week is the difference in

altitude between the base and the rim of some of these craters is like four

kilometers. That's about two miles.

We talk about Denver, the mile high city. Imagine standing on the edge of

something twice the altitude or more of Denver looking down. There is an

amazing movie they showed us of a little tiny sad little lander craft coming in

and just perching on the very edge of one of these craters.

Fraser: Nancy, one of the writers did a story about that on Universe Today. We've got

the video on the site. It's kind of scary.

Pamela: The reason that we're looking to do this is when you land at the equator of the

moon, in daylight you're several hundred degrees. When in darkness, you're at

minus a couple hundred degrees. Pick Fahrenheit or Celsius it really doesn't

matter it's really huge swings in temperature either way you go.

Once you get down into one of the craters in constant darkness the temperatures

stay constant. One of the things about electronics is they don't really like to

have their temperature messed with. We can engineer things that work at a

couple hundred degrees and we can engineer things that work at a negative

couple hundred degrees. It's hard to engineer things that can survive huge

temperature swings.

If we go to one of the poles of the moon you can stick your habitats down in the

shaded part and just keep people warm and stick your solar panels straight up

and they will be in constant daylight. So you have constant power and thermal

regulation. It's just a lot easier to function that way.

12

Fraser: You could have the sunlight just a few tens of meters away from your habitat

and still be safe.

Pamela: One of the ways they phrased it was you can be down in a constant darkness

area and just raise your hand and the simple act of raising your hand that is

above your head, your hand will be in perpetual sunlight.

Fraser: I can't wait until that exploration starts happening.

Pamela: Just a few more years.

Fraser: Just a few more years. The missions are going to be launching just within the

next year and it seems like it will start steamrolling from there.

Pamela: We have LCROSS and LRO are launching on the same rocket in I think

October of this year. LCROSS is this really cool mission that they're going to

basically plow objects into the surface of the moon making artificial craters,

making our own space craft into meteorites and see what dust gets chewed up

into the air. It's going to be neat work.

Fraser: All right, well I think we'll be covering that as we go for a much, much future

show.

Pamela: It was a great experience and next year you need to come with us Fraser.

Fraser: Will do.


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

]]> http://www.astronomycast.com/astronomy/ep-80-craters/feed/ 13 Ep. 70: How To Win a Nobel Prize http://www.astronomycast.com/astronomy/ep-70-how-to-win-a-nobel-prize/ http://www.astronomycast.com/astronomy/ep-70-how-to-win-a-nobel-prize/#comments Tue, 08 Jan 2008 16:05:32 +0000 Astronomy Cast http://www.astronomycast.com/astronomy/ep-70-how-to-win-a-nobel-prize/ how to get a career in astronomy. Now that you've got your career in astronomy, obviously the next goal is to win a Nobel prize. We're here at the American Astronomical Society meeting in Austin, which is just one tiny step that a person has to take before you get that Nobel prize. Before you get that call in the middle of the night from Sweden, you're going to need to come with an idea, do some experiments, write a paper, get published and a bunch of other stuff. This week, we'll tell you all about it. Episode 70: How to Win a Nobel Prize (13.9MB)]]> Pamela and Fraser recording the show
Just a couple of shows ago, we showed you how to get a career in astronomy. Now that you've got your career in astronomy, obviously the next goal is to win a Nobel prize. We're here at the American Astronomical Society meeting in Austin, which is just one tiny step that a person has to take before you get that Nobel prize. Before you get that call in the middle of the night from Sweden, you're going to need to come with an idea, do some experiments, write a paper, get published and a bunch of other stuff. This week, we'll tell you all about it.

Episode 70: How to Win a Nobel Prize (13.9MB)

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    Transcript:

    Fraser: Just a couple of shows ago we showed you how to get a career in Astronomy. Now you have your career as a research astronomer. Obviously, the next goal is win a Nobel Prize. We’re here at the American Astronomical Society Meeting in Austin, which is just one tiny step a person has to take to win that Nobel Prize.

    Pamela: And there are a few Nobel Prize winners floating around this meeting.

    Fraser: So it’s not impossible.
     
    Before you get that phone call in the middle of the night from Sweden you will need to come up with an idea, do some experiments, write a paper, get published, and a bunch of other stuff. I’m probably over-simplifying it Pamela.

    Pamela: Oh, way over-simplifying it.

    Fraser: Obviously not everyone is going to win a Nobel Prize, but why don’t we start somewhere and talk about how people can go from zero to getting their research done.

    Pamela: Well, in general you have to start with an idea. You have to start with a question, a “what if� and work on trying to solve that “what if.� Nobel Prizes have gone to people who said, “what if you look at the Universe in the radio; what if you explore what is coming through galaxies by simply tuning your telescope to look at radio light instead of looking at optical light?�
     
    There are all sorts of different people who have simply said “well what if� and then there’s the hard part; it’s easy to come up with the “what if�.
     
    You then spend years following that “what if� with careful theoretical work with careful building of instrumentation, with carefully looking at your noise to see what is it in the noise that no one else has ever discovered.
     
    The cosmic microwave background came from a group of scientists working to study the microwave emission of our galaxy and instead coming up with the microwave emission of the universe.

    Fraser: I read that one of the ways that some of the greatest research happens is that it starts out with someone looking and going, “huh, that’s funny.�

    Pamela: And most of us go huh that’s funny and we blame our instruments and move on. The truly great people won’t let things go. They just keep delving in and exploring deeper until they’re able to say, “well I’ve ruled out everything. This is something new. This is something exciting.� Then they followed up with figuring out what it is, and it’s a collaborative process with different people shaking ideas out on other people who can then go, “no that’s crazy but what if�…and you follow all the “what ifs� until you find the truth.

    Fraser: Okay. Let’s start at the beginning then. Let’s say you have an idea or you look at your data and think, “huh, that’s funny.� What’s the next step?

    Pamela: Math.

    Fraser: Okay.

    Pamela: The first step is you go through and do a statistical analysis. You see if you can repeat it. You have to be able to repeat something. If it happened only once never to be repeated again, it probably wasn’t real.

    Fraser: Right, I guess what I’m saying is how will you get access to telescopes? How will you get access to the equipment you need to even follow your crazy ideas?

    Pamela: Let’s say you’re not trying to figure out what the noise in your data is but rather you come up with this idea of “I think foo is true about galaxies� and you want to figure out how to prove to the rest of the entire scientific community that is true. Well the first step is you do a literature search and make sure no one else has ever studied foo.

    Fraser: So where would you do a literature search?

    Pamela: There are two places to go. There is the NASA ADS website which is pretty much a collection of all the published journals. Some of them unfortunately, you have to pay huge subscription fees to get access to the most recent articles. But there is hope.
     
    There is another site XXX.lanl.gov It’s ArchiveX, it sounds like a porn site but it’s run out of Lawrence Livermore National Labs and it’s where pretty much everyone goes to dump a copy of their latest research. Often people dump a copy before it has even gone through peer review to get feedback from the community – what questions do people have and what ways can you make your paper better before you take it to publication?

    Fraser: Right. These all have search engines you can put in key words, you can put in search of the text. It’s all available, you can read their research and make sure that whatever your idea is, nobody else has, or you find what everyone else thinks on the subject and you can decide whether your thinking is absolutely brand new or just a variation of what somebody else thought about.
     
    I guess when you see what other people thought about it helps you search and refine your thinking and you come up with new ideas.

    Pamela: Then you need some sort of an infrastructure to put your idea in. “I think Galaxies might have foo becauseâ€?… And then you go through and demonstrate what is the evidence that this could be out there waiting to be found. What are the breadcrumbs that are leading you to discover this new foo about galaxies?
     
    Once you’ve put these breadcrumbs together and found the path through the woods, then you write telescope proposals. You write grant proposals. You try to get the time and the money that will allow you to study this effect. This is it’s own peer-review process.
     
    You send out a proposal for telescope time and you’ll either get telescope time or you’ll get feedback that says, “well we didn’t give you time because we are concerned about the following things. Follow up on this. Tell us more; convince us better�.

    Fraser: You have to sell to the telescope managers that your idea is worth exploring.

    Pamela: It’s actually a committee of hopefully your peers or the people you hope to be peers with in the future. It’s a select group of scientists who sit down and it’s not always the same group of people every time. They go through all the proposals and sometimes hundreds of proposals looking for forest nights of telescope time to be available to them.
     
    These people go through and use their wisdom and ability to use the scientific method to examine your argument. Think of them as the jury in a court case and you are the lawyer making your opening statement. You have to sell your idea and only once you’ve convinced them that your idea is worth pursuing do you get the ability to pursue it.

    Fraser: But as you’ve said, there are other avenues you can go to. There are networks of amateurs and there are other ways. You make the same pitch to multiple missions to multiple telescopes.

    Pamela: One of the best ways to do it is first you go to some easily accessed ground-based telescope and get some preliminary observations. With the preliminary observations you say either we have a hint of this being possible or we can’t eliminate this as being possible because the observations aren’t good enough using this telescope so clearly we need a bigger and better telescope.

     
    They want you to first use the cheap, easily available resources before you can get the Hubble Space Telescope time – the very large telescope time. It’s a matter of did you do your homework or not. It’s big resources and there are not a lot of resources out there to share.

    Fraser: So you have written your proposal, your peers have come back and said this sounds like it’s worth pursuing so they’ll schedule you time on the equipment?

    Pamela: You get time on the equipment; they then often just ship the data to you. A lot of the telescopes now are what they call Q-based. You say, “these are the conditions that need to be met for my observations to be taken,� and a night assistant automatically gets your data and ships it to you either over the internet or perhaps on a DVD.

    Fraser: So you don’t have to go to the telescope?

    Pamela: No, not at all.

    Fraser: You don’t have to head out to space to look through the Hubble?

    Pamela: No, definitely not that one.

    Fraser: But in many cases, the proposal is approved and you’re in. At the time that they promised your data will come to you and you can start crunching it.

    Pamela: It’s all beautiful magic. Once you get your telescope data that is just the start. It can take months to get your data reduced to a point where you have numbers you believe are actually true.
     
    You get your data, you reduce it, you play with it, try this, try that and a couple of months down the line you have something where you can make graphs and plots.
     
    From your graphs and plots you have to try to figure out what does my graph and my plot mean? In some cases you can get completely new science just by graphing two variables no one every thought to graph before.

    Fraser: But in many cases you have an idea of what you should be expecting with your galaxy theory and you are now looking through the data and checking to see if your theory matches reality.

    Pamela: Yes.

    Fraser: And as you are saying, there could very well be any number of interesting things that poke up in the data that are completely separate from what you’re working on and that probably must just work into brand new proposals to look for more information.

    Pamela: Every new question you answer ends up creating ten, fifteen, twenty, a thousand more questions, more ideas, more things you just need another ten nights of telescope time to explore.

    Fraser: But even if you get a no result, that’s still useful because that just means that your theory is wrong and that’s okay.

    Pamela: Or sometimes you just simply haven’t come up with a better way to do something.
     
    One of the more frustrating aspects of my doctoral dissertation is that I successfully proved that that if you look at one radio source you have roughly 23% probability of finding a cluster of galaxies around that. We already knew that. But if you look at a grouping of six radio sources, you have a 27% a whole 4% better chance of finding a galaxy cluster. It wasn’t really easy.

    Fraser: Intriguing.

    Pamela: It wasn’t really useful though because it takes a lot of time to find the clustering and prove that it is real. It was a very sad result, but is was a true result and it was worth sharing to prevent anyone else from following this bad avenue of exploration.

    Fraser: All right, so let’s say that you got your data, you’ve crunched your numbers and you believe you now have a result.

    Pamela: Then you publish. Often the first step is coming to a meeting like this one, the American Astronomical Society meeting and putting a poster presentation together.
     
    This is where you have a 48-inch x 48-inch sheet of paper to convince everyone of the vague outline of your idea. Show your graphs. Give captions. Give a few hundred, maybe a thousand words of text in big enough letters that someone slinking past with their coffee trying not to attract any attention will be able to read as they slink past.

    Fraser: I can’t overstate that it really looks like a kid’s science fair with posters around. It really seems like you would expect it was a lot fancier but it is like a big piece of paper with a bunch of pretty pictures on it and some graphs and a person standing beside it trying to get people to come take a look at it.

    Pamela: It’s just amazing the diversity of people. My very first time I presented was at AAS in San Antonio, TX and the person hanging the poster next to me was Erica Bonvetnse (?) who had written the textbook I was using that semester and was another variable star astronomer and many, many other things. She’s just awesome.
     
    I totally fan-girled over this woman older than my grandmother – that’s probably not true. But I made her sign her book and then she just stood there dutifully next to her poster just like I, the little meek undergrad did.
     
    So you see everyone from high schools students in some rare cases to the most senior faculty standing quietly next to their poster waiting for someone to come by and actually care.

    Fraser: So you have to do your time with your poster.

    Pamela: Yes.

    Fraser: All right. That’s only one part of the conference. The other parts are the meetings.

    Pamela: There are meetings and oral presentations, but posters are the primary way to convey information. There are also 5-minute oral presentations.

    Fraser: Posters are the primary. It blows me away that standing beside a poster is the way that you communicate your research and your ideas to other astronomers.

    Pamela: Well what’s great about is if your options are give a 5 minute oral presentation or present a poster, with your 5 minute oral presentation you have no time to say anything – that’s 3 overhead slides; 3 powerpoint slides.
     
    At your poster, you can stand there and you can have a dialogue with your peers. You can find out who has data on this source that is sitting in a drawer unprocessed because they took it for some project they decided not to do. You can interact, you can get great ideas.
     
    That is what’s important about doing these poster and oral presentations is dialoguing with other people. Finding out what don’t you know that is hidden in somebody else’s head or drawer or some journal article that you just missed because it is easy to miss one or two. There are thousands and thousands out there.
     
    You go through this process of dialogue. Science is a collaborative effort. Very few people work in any sort of isolation and we generally refer to the people who work in isolation as cranks because science is dialogue. Each person’s idea is growing on everyone else’s ideas.
     
    Once you’ve gone through these presentations, then you’re ready to sit down and spew out your five to ten page journal article that you then submit to a journal for final publication.

    Fraser: So once you’ve gotten all the feedback from your poster presentation, you’ve sat in a bunch of meetings, you’ve had a chance to collaborate with some of your peers, you then go back to your quiet office space and write up your findings.

    Pamela: Yes. You write up your findings.

    Fraser: Now that you have a journal article what do you do with it?

    Pamela: You hope that somebody reads it. This is where if you write a really good paper and it catches someone’s attention, if you have a really remarkable finding you might actually write a press release for it or go to your University Press Officer and get them to write a press release for it. If you’re lucky, people will read your paper and most papers really get read like ten times.

    Fraser: Where will they read your paper?

    Pamela: In the journals that come out.

    Fraser: So your paper isn’t guaranteed to go in a journal.

    Pamela: No, you take your paper and submit it. The step that we all painfully try and forget is when you get your referee’s report back.
     
    So, you submit your paper to the journal. The journal then finds someone who’s not one of your direct collaborators and is quite often your direct competitor, sends your paper to them and asks them should we publish this? They will generally say, “yes, but make all of the following corrections.� Often you have to go through three rounds before you actually you get the yes.
     
    The first round will be: this is worth publication but needs serious revision. You then revise. It then comes back and says: much better and if you’re really lucky that’s when they say yes fix these four sentences that you wrote stupidly.
     
    Occasionally you have to go to a third before they finally say yes, this is worth publishing. Often referees are extremely useful since they are coming at it from outside of the problem they are able to say, I think I know where you’re going with this idea but I shouldn’t have to guess. Flesh this out so that anyone reading this knows what you’re thinking.
     
    Sometimes they write just the most amazingly vague things like expand on paragraph six. And I think, what about paragraph six do I need to expand upon? You’re just wondering, how dumb can this person be?

    Fraser: Of course, any of the people who would have worked on any of Pamela’s papers in the past they were wonderful.

    Pamela: Right and the grant process is the exact same way. So you get back these referee reports, make all the changes, eventually get your paper accepted and then it often comes out several months later.

    Fraser: And that’s the peer review process, right? You’re submitting your paper to your peers – in many cases your enemies – and they’re trying everything they can do to find a hole in what you’ve thought of. Trying to make sure the words you’re using are as clear as possible before the journal is willing to publish it.
     
    So you run that gauntlet, you do the final edit; no one else can nitpick any other problem with your journal article; it gets published into a journal. What are the journals?

    Pamela: The primary ones in astronomy are the Astronomy Journal, the Astrophysical Journal, the publications of the Astronomical Society of the Pacific, the monthly notices of the Royal Astronomical Society, Nature and Science and Astronomy and Astrophysics. Nature and Science are big only because they have the biggest press engines.
     
    A lot of really great science comes out in the Astrophysical Journal that is totally worth being in Nature and Science but the authors just don’t feel like jumping through that hoop. Nature and Science are hard to work with.

    Fraser: They want to make it all pretty slick with pictures.

    Pamela: With the Astrophysical Journal, you know it’s going through peer review, it’s going out to your peers which doesn’t necessarily happen with Nature and Science. You get your journal article in Astrophysical Journal or one of the other journals and now you hope somebody reads it.
     
    If you’re lucky and people read your work, that’s when you start getting invited to give university talks. You are invited to give talks at conferences like this one and at other conferences out there and your idea starts to build and is shared and starts to become a foundation of what we do.

    Fraser: So what will happen is future researchers will be referencing your work in their work. Citations, is that right?

    Pamela: Citations are sort of the thing that we all want the most. It’s one thing to publish ten journal articles a year, but if no one ever cites them or no one ever reads them, what good are they?
     
    Given the choice of inviting a speaker who’s written three papers that each have a thousand references and that happens very, very rarely, but it occasionally happens, or someone who’s written a hundred papers that have never been cited by anyone other than the author, go with the person with a thousand citations. They clearly did something that somebody (and in this case a lot of somebodies), care about and need to know.

    Fraser: Right and so it’s almost like the citations are the votes from other researchers that the work that you’ve been doing is of value and is a high contribution to the field.

    Pamela: It’s just like how many links does the Podcast website have; how many links does the blog have pointing at it.

    Fraser: It’s almost like the same model that Google works on that the more links to a website the more popular Google has decided that website is so the more likely it is to show up in future searches.

    Pamela: The way it actually ends up happening in some cases is someone finds a cool effect and that cool effect ends up taking on the names of the authors. So you have the Butcher-Oemler effect in galaxy evolution. You have the Geller Hook diagram. These are all people and those are the names on the journal article that brought forward this new idea that now bears that idea’s name.

    Fraser: You get to have your name just run along with it for the rest of the time that it gets used.

    Pamela: Forever.

    Fraser: That’s the way to go.

    Pamela: Yes. So now anyone who is out there doing large-scale structuring Geller Hook…is still there. For a long time galaxy formation was the Agen Linden Bell model. I hope I got those names correct otherwise I’m going to be laughed at later. But Searles Zin model – there’s all these different it’s just the names of the people on the article and that’s what you remember and those names go on to sum up all the ideas in those journal articles, those key papers to our fields.

    Fraser: If you want to be a working astronomer, how often should you be publishing?

    Pamela: It depends on what you do. There are people out there who are amazingly prolific and put out one paper a month or more in some cases. All because you’re chewing out a whole lot of papers doesn’t mean you’re doing excellent science.

    Fraser: No, but in some cases I guess – like Mike Brown at CalTech who is the person who found the tenth planet. I guess he’s got the right technique, the right team…

    Pamela: And he’s just chewing out discoveries.

    Fraser: Exactly. Oh, new planet, new large Kuiper Belt object and just keeps them coming out. In those cases I think you don’t really no need to slow down or stop. But if you’re going to come up with something really deep in foundation you might as well take your time and get the citation.

    Pamela: It depends on what field you’re in. If you’re a theorist, you might spend a year or two carefully delving through the mathematics and get one publication out of it and you worked very hard the entire time.
     
    In other cases you might be someone who is studying things that it takes two years worth of observations and then all of the analysis that goes in the observations.

    Fraser: Think of the people on the Gravity Probe B mission where it will take two years or three years for that to finally gather all of the data to be able to decide and in the end it will be just one sentence like: Yes, Einstein was right again.

    Pamela: The number of publications that makes sense for you is really going to depend on what type of science you’re doing. There are people like Michael Brown who just chew out papers at a phenomenal rate and then there are other people that two papers a year and they are highly respected scientists. You just have to put all the different pieces together.

    Fraser: That’s kind of good for the regular folk but now the people who really want to win the Nobel Prize, are there any other further steps you can take or is it you’ve already done your bit?

    Pamela: You’ve either got it or you don’t.

    Fraser: So you either thought of something foundational that’s going to change everything or keep working.

    Pamela: One of the key aspects that I’ve seen in all the Nobel Prize winners that I’ve interacted with is these are the people that when you walk through the University halls at 8 p.m. are at their desk. When you walk through the hallways at 6 a.m., they’re at their desk.
     
    They go home for 6 hours maybe and they’re constantly dedicated, they run a tight ship in terms of keeping their grad students on track and keeping their undergrads on track. Everyone works hard, dots all their I’s, crosses all their T’s, pays attention and is thorough.

    Fraser: There is a level of almost organization and hard work and focus and dedication that goes above and beyond the regular researching that happens.

    Pamela: These are the type of people that in a few cases after they get the Nobel Prize, they decide to go and play in another field and within a matter of months they’ll be at the top of that field too. There’s just a level of both genius and dedication that qualifies someone to be capable of getting a Nobel Prize.

    Fraser: In many cases I know the Nobel Prizes aren’t awarded until in some cases ten or twenty years. It’s almost like you have to wait until the research is totally incontrovertible, that everyone assumes it is completely true and they use it repeatedly.

    Pamela: It becomes part of the canon.

    Fraser: It’s not like you’re going think this year we came up with a wonderful discovery and later this year we’re going to get a call from Sweden. It’s this year we’ll come up with a wonderful discovery and then over the next ten years it’s proven and re-proven and everyone really thinks it is right.
     
    Ten years after that if things have really settled down then you’ll get your call. You can almost, from what I’ve heard from people who’ve got it, you can start to feel that you’re in that zone; you’re starting to have a chance to win one of the prizes. I thought this could be easy, but I guess it’s not.

    Pamela: No, it’s not.

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

]]> http://www.astronomycast.com/astronomy/ep-70-how-to-win-a-nobel-prize/feed/ 1 Ep. 53: Astronomy in Science Fiction http://www.astronomycast.com/astronomy/episode-53-astronomy-in-science-fiction/ http://www.astronomycast.com/astronomy/episode-53-astronomy-in-science-fiction/#comments Mon, 10 Sep 2007 15:00:34 +0000 Astronomy Cast http://www.astronomycast.com/interviews/episode-53-astronomy-in-science-fiction/ Episode 53: Astronomy in Science Fiction(27.4MB)
 
]]> This week\'s episode was recorded live at Dragon*Con 2007
This is a very different episode of Astronomy Cast. As we mentioned last week, Pamela recently attended the Dragon*Con science fiction convention in Atlanta, Georgia. While she was there, she participated in a special live edition of Astronomy Cast with special guest Dr. Kevin Frazier. Kevin is a NASA scientist, and the science consultant for the TV shows Battlestar Galactica and Eureka. He and Pamela work through physics and astronomy in popular science fiction. What they get right, and what they get wrong… so very wrong.

Episode 53: Astronomy in Science Fiction(27.4MB)
 

]]> http://www.astronomycast.com/astronomy/episode-53-astronomy-in-science-fiction/feed/ 4 Ep. 40: American Astronomical Society Meeting, May 2007 http://www.astronomycast.com/astronomy/episode-40-american-astronomical-society-meeting-may-2007/ http://www.astronomycast.com/astronomy/episode-40-american-astronomical-society-meeting-may-2007/#comments Mon, 11 Jun 2007 18:54:01 +0000 Astronomy Cast http://www.astronomycast.com/meetings/episode-40-american-astronomical-society-meeting-may-2007/ Episode 40: American Astronomical Society Meeting, May 2007 (13.0MB)
 
]]> The AAS goes to Hawaii.
Once again, Pamela does her duty as an astronomer and joins her colleagues at the American Astronomical Society's meeting, held in May, 2007 on Honolulu, Hawaii. With all that sand, surf and sun, how did anyone get any science done? Pamela tracked down the interesting stories, and brought them back so we could analyze them.

Episode 40: American Astronomical Society Meeting, May 2007 (13.0MB)
 

Galactic Tidal tails

Spinning Black Holes

Planets Around Unusual Stars

 

 
Download the transcript
 

 

Transcript: American Astronomical Society, May 2007

Fraser Cain: We're going to take a bit of a break this week and talk about some of the interesting research you picked up while you were there – some of the latest breaking news, the stuff that's going to make you have to go at your textbook with a pen to fix them.
 
[laughter]
 
So, you've got a bunch of topics, there's going to be no theme to this. Just to warn people in advance, in some cases the audio quality is a little hard to understand, so we apologize in advance and we'll take better equipment to the future conferences.
 
Where are we going to start?

Dr. Pamela Gay: I think starting with the very first press conference for the meeting might be a good place.

Fraser: What was that about?

Pamela: The first press conference, right off the bat, we had a young post-doc from your neck of the woods, from the University of Victoria in British Columbia. Jorge Penarrubia presented on the first virgin dwarf galaxy we've ever found, and if that title doesn't peak your interest, I think the fact that it just sort of came out of nowhere and is headed straight toward Andromeda… well, violence always attracts attention.

Fraser: All right, so where did this come from?

Pamela: Well, as near as we can tell, this small dwarf galaxy formed on its own and it formed away from the local group. As the Andromeda galaxy grew and grew and grew and became the large galaxy we know today when we look through binoculars, its gravity eventually got to the point that it was able to start sucking stuff from the nearby Universe toward it. One of the things it started to suck in is this new dwarf galaxy called Andromeda 12.
 
This is the first dwarf galaxy that anyone has ever found that hasn't already interacted with a giant galaxy. This is where the whole idea of it being a "virgin" galaxy comes from: it hasn't been touched gravitationally and hasn't had any of its stars, its dark matter, nothing with it has been disturbed. For the first time we can look at what a building block of a galaxy looks like before it's been incorporated into being used to build something.

Fraser: So every galaxy that we see has already had some interactions and has changed the way it looked. What role does the dark matter play in that?

Pamela: Rather than having me explain it, why don't we have Jorge explain it?
 

Dr. Jorge Penarrubia: So the dark matter from dwarf galaxies forms what are called tidal streams, and these tidal streams follow the orbit of the dwarf galaxies initially. Sometimes this dark matter gas distributes around the host galaxy and contributes to the dark matter halo of the host galaxy.

Fraser: Oh I see, so the dark matter is stripped out of these dwarf galaxies and added to the halo of the larger galaxy. All the dwarf galaxies we've already seen have already had this process happen to them.

Pamela: They've already been pillaged – and it's not just the dark matter that's been pillaged. Let's listen to some more of what Jorge had to say:
 

Dr. Jorge Penarrubia: For instance in the Milky Way you have the stars that were born here, and the stars that were born in other systems (like dwarf galaxies) – you have both things, and actually they're not isolated. For instance the in-fall of dwarf galaxies can actually trigger star formation. So it's quite complicated process and we're starting now to learn about – well, it's not really learn, we have a clear picture as to it.

Fraser: Right okay, so the dwarf galaxy slams into one of the larger galaxies, contributes its stars, gets dark matter torn away, you get star-formation and goodbye galaxy.

Pamela: Goodbye galaxy, and all that's really left behind is the stuff that forms our galaxy and occasionally when we're lucky we get to see some tidal streams, but we're going to be talking more about that later.

Fraser: Now is this going to happen to this galaxy?

Pamela: It's just a matter of time; it's currently on a heading that is sending it straight toward M31, the Andromeda galaxy. It's going to get there eventually and whip around, get its dark matter stripped out, get shredded into a tidal stream, and it also will eventually become part of our galaxy when our galaxy and the Andromeda galaxy merge. It's all a matter of timescales. I have to admit I didn't catch the timescale that Andromeda 12 is going to get to M31, the big Andromeda galaxy, so I'm not sure if we're going to merge first or if it's going to merge first. Eventually, all these galaxies are going to form one much, much larger system.

Fraser: Yeah, can we call it Milk-dromeda?

Pamela: [laughing] Something like that.

Fraser: Milk-dromeda Way? Yeah.
 
Okay, so what else did you learn?

Pamela: Later on in the week, there was a press conference on spinning black holes. Everyone gets excited about black holes, and these weren't just normal, run of the mill black holes, they were talking about what happens when you take two galaxies (say, the Milky Way and Andromeda), slam them together and you observe the super-massive black holes in their cores hopefully merging into an even more super-massive black hole.

Fraser: Okay, and so what were they expecting to see?

Pamela: Well, let's listen to what one of the researchers had to say. Laura Brenneman was kind enough to sit down and explain a little bit of their physics to us.

Laura Brenneman: Basically what we've done is we've created a new model that allows us to look at the x ray spectra from the accretion disk very close to the black hole. We're interested in the disk in particular because of the space-time that is as close to the black hole as we can get and still observe electromagnetically.
 
So when we look at spectral signatures from this material close to the black hole, what we expect to see is that rather than seeing narrow void profiles that you would expect to see in spectral lines in a laboratory, what we're actually thinking we're going to see is signatures of relativity. Special relativity, general relativity, also Doppler shifting within the disk.

Fraser: So they're actually seeing effects on the elements around the black hole that match predictions from relativity?

Pamela: They're seeing special relativity, they're seeing general relativity, they're seeing massive Doppler shifting. All of these things are communicated through the line shapes of the elements that make up the accretion disk around these black holes.

Fraser: When you say "line shapes" what does that mean?

Pamela: When you take the light from something (anything, the Sun, say), and spread it out, you can create a rainbow. We've all seen this happen: bits of glass hanging in windows will end up casting bits of rainbows onto walls.
 
If you spread that light out enough, what you can start to see is dark lines where an element has absorbed the light out of the Sun. You might see a line that corresponds to a transition in hydrogen. You might see a line that corresponds to a transition in iron, where the atom absorbs the light and an electron jumps to a different energy level; lots of neat physics is happening.
 
Well, if you're dealing with something that's just like the Sun and hanging out near-by, not moving a lot relative to us, the lines are symmetric: they are the same shape on the red side and on the blue side, and they're just nice, gaussian profiles. When you start to add in all these other effects, what you end up with instead is a line that is really skewed toward the blue. You see massive peak in the blue and then you see it slowly tapers off, tapers off, tapers off, toward the red. This is because you have all sorts of other effects from relativity, from just the fact that the accretion disk is rotating really fast.

Fraser: How fast?

Pamela: That's complicated! First of all, there's the minor problem that we're moving, it's moving, time's relative. Ignoring that, with a 10^7 solar mass black hole, you end up with a rotation rate where it goes all the way round once every ten minutes for an accretion disk that is on the verge of spinning itself apart. This is where it's spinning so fast that the centrifugal force wins out over gravity and everything just sort of blows itself apart and you're left with a naked singularity.

Fraser: And that's where it has no accretion disk around it, because it's spinning so fast?

Pamela: Exactly. That means in reality, they're going to be rotating slower than that. But, we're looking at something that is rotating as fast as it can without blowing itself apart, and the inner parts are going around every ten minutes. Things are going significant fractions of the speed of light. It's scary physics in there.

Fraser: Okay. What's next?

Pamela: What is next is more tidal tails. This was a meeting that I have to say made me and my love of small things that are in the process of getting destroyed, very, very happy.

Fraser: I didn't know that about you!

Pamela: [laughing] Well, when it comes to celestial objects, they're much more interesting when they're getting destroyed.

Fraser: Okay.

Pamela: The next thing that was up was more discussion of tidal tails. This is sort of also a running joke in the press room of every meeting there seems to be a new press release on tidal tails.

Fraser: Hold on! What's a tidal tail, then?

Pamela: Instead of me explaining it, why don't I have one of the researchers explain it. Carl Grillmair of Caltech and IPAC was kind enough to sit down and talk to me for a while about this, and he had some really neat things to say:

Dr. Carl Grillmair: Well they're the relics of whatever was there. I think a lot of people are actually surprised right now that they're actually there. People had always assumed from the beginning that even if the galaxy cannibalizes dwarf galaxies and globular clusters and so on, it will quickly precess or be scattered into giant molecular clouds and random orbits, and it will just be this big soup of stars, which is what everyone assumed was what the halo was, and the bulge and all these things.
 
In fact, we've seen, like today I showed (well, maybe I didn't actually show you, but it was on my poster) there's an 84 degree – absolutely narrow, quarter of a degree wide for 84 degrees across the sky. That would've taken billions of years to form and it was still in tact. There was no obvious sign of scattering in any direction. The halo has to be extremely smooth.

Fraser: Okay, so we've got these long streams of stars and globular clusters in huge arcs across the sky – he said 80-something degrees. How much of the sky is that?

Pamela: So imagine something that stretches from looking at the constellation Gemini all the way up to the north star. They stretch from the horizon to zenith as you look out across the sky.

Fraser: Zenith is the… point straight up?

Pamela: The point straight overhead.

Fraser: Right, okay. So if I look down at the horizon, I would see the beginning of the tail, and then I could look straight up and see the end of the tail, and that is a dwarf galaxy that has been spaghetti-fied.
 
[laughter]

Pamela: Well, spaghetti-fication is reserved for black hole destruction.

Fraser: Right, right, right – but I think it's appropriate here.
 
But yeah – torn into a long stream.

Pamela: Idly disrupted.

Fraser: "Idly disrupted" that's a very fancy word for it
 
[laughter]
 
So what's the process then, that makes this happen?

Pamela: Tidal disruption! As they come in, their ability to hold themselves together is lost as they're getting pulled on by the Milky Way's gravity. As they fall in, the leading edges are going to accelerate forward, the back ends are going to be slower at falling in, and everything stretches out as they fall down the potential well.
 
What's really neat about these is as they go, they're falling downhill, basically. If you imagine our Universe as this four-dimensional thing where we see three dimensions and that fourth dimension is traced out by everything rolling around, the arcs, the streams these things shape on the sky… that is the path of rolling around in the bowl made by our galaxy.

Fraser: So what was the new research that they had come up with this time around?

Pamela: In this case, what he was primarily talking about was we found another one. As he and I sat down and talked, he also brought up the fact that as we trace these things further and further out, we're finding things that don't entirely make sense. They're turning up at the ends, so that implies maybe there's bumps (but not often) out in the halo of our Milky Way. Those bumps would have to be made out of dark matter.
 
So yes, the halo seems to be smooth, smooth, smooth. But occasionally, there is a little bump here or there. That was kind of neat to hear him talk about.

Fraser: All right: moving on. What's next?

Pamela: What's next is how life around M-type stars might not be quite as cushy as we would've thought a couple weeks ago when we started having all these press releases about Gliese 581.

Fraser: What's an M star?

Pamela: An M star is a little tiny dwarf star. In some cases, they're just 10% the size of our sun. They're really red, they're really cool and they basically live forever. They live sometimes as much as 40 billion years while still just burning hydrogen in their core.

Fraser: So in theory, that would give a planet a long time for intelligent life to happen.

Pamela: Exactly. The problem is these stars don't start out nice and calm. In fact, life's a little bit rough, but rather than me describe it, let's listen to Ed Guinan sit down and talk with us about it:

Dr. Ed Guinan: We found the relationships between coronal x ray machine. With age the young ones are very active – they have flares and lots of x rays. By the time they get to the age of Proxima Centauri, which is 6 billion years old, they've died down by a factor of 2 or 3 hundred, and then beyond that even more. This is mainly because the stars are spinning down; they're losing their angular momentum.

Fraser: Okay, so the stars start out quite violent, but then they settle down over time?

Pamela: And life could still be possible if you could find a way to get a strong enough magnetic field to create a strong magnetosphere around these planets. The problem is that to have a habitable world around an M-type star, you have to place the planet right next to the star. When you do that, you end up with tidal locking. Just like we have the Moon always shows its same face at the planet Earth, these planets always show the same face to their star. To get a magnetic field, you have to be rotating quickly. To be rotating quickly, you can't be tidally locked to your star, so there's this weird conundrum of how do you make something that survives this violent 1.2ish billion years of the star's early life so you can have a civilization that then stretches on for just about 40 billion years? It's problematic.

Fraser: Okay, so the planet might get that tidally locked really early on, and not get a chance to build up the magnetosphere and then just take it on the chin for millions and millions and millions of years with these bouts of radiation.

Pamela: These bouts of radiation don't just destroy any DNA of any life in the process of trying to form. These bouts of radiation also blow away chunks of the atmosphere. We're able to hold onto our atmosphere because our magnetosphere protects us from having all of these high energy particles raining down on the upper parts of our atmosphere. Without it, bad things would happen, things would get blown away.
 
Mars is representative: poor Mars has no magnetosphere, it's core already cooled off and its magnetic field already faded out as the core froze. So it's losing its atmosphere not just because its small and can't hold onto the fastest moving gas particles, but also because the solar wind is blowing away parts of its atmosphere.
 
So these planets, if they form, would have the star blowing away the atmosphere and they'd get blasted by radiation. Neither of these things is particularly inspiring toward the formation of life.

Fraser: So what were the results of this research, was it good or bad on that direction?

Pamela: The results were sort of like, "oh dear, we need to find a different way to get these planets into the habitable zone other than they form there initially."
 
One of the possible solutions is: if you have a planet that forms far away from the M star, and stays there for the initial few billion years, or creeps in very slowly and enters the habitable zone after the M star has stopped having these huge flares, these huge blasts of x ray and gamma ray energy, then (if it migrates in later), life can develop later.
 
So you have lots and lots of time, it's just a matter of figuring out how to get everything where it needs to be in the proper timescales.

Fraser: These are some planets around some of the smallest stars, but you actually looked at someone who was looking at planets around some of the largest stars too.

Pamela: In the exact same press conference where they were talking about these flaring M stars that can be potentially dangerous for planets, they also had John Asher Johnson talking about how you can find planets around really big, bright, A-type stars (or at least, around the relics of really big A-type stars). Let's listen to what he has to say about it:

John Asher Johnson: So we decided to look for planets around stars that are more massive than the Sun, commonly called A stars. You can't search for planets around A-type stars when they're on the main sequence.

Fraser: Okay, so these A stars are larger than the Sun. What kind of mass are we looking at?

Pamela: They're typically 2-4 solar masses, so they're bigger but not hugely bigger.

Fraser: If I understand the way astronomers search for planets, they use this spectroscopic method where you've got the gravity of the planet yanking the star back and forth and back and forth and we're able to calculate the velocity of the star moving toward and away from us, to be able to get a sense of what the mass of the planet is. So you get a more massive star, that's got to be hard.

Pamela: That's got to be hard, and it's even more complicated than that. But let's listen to how he explains it:

John Asher Johnson: What few lines they have are smeared out by their rotation. Broad, smeared out lines contain much less Doppler information than narrow lines. So the end result is you can only do it by the 100 meter precision. To give you some context, a hot Jupiter planet has an amplitude of about 100 meters per second. So you can't even see the hot Jupiter planets around these A stars.

Fraser: Okay, so he said that they're looking at stars outside of the main sequence. Why is that?

Pamela: Outside of the main sequence, these stars expand out. If you think of an ice skater, when she pulls her arms in, she starts spinning faster. Conversely, if you watch her put her arms out, she slows down. When these stars move off the main sequence, they bloat out and slow down their rotation. The lines they have become narrower – they're not Doppler spread out anymore.
The stars also cool off, and when they cool off there's more atoms that still have electrons available to create spectral lines. In a really hot star, everything's ionized. When an atom is ionized, it doesn't create spectral lines, it just sort of sits there going "ahh, I have no electrons!" Cool it off, let it collect an electron or two, and now those electrons are available to grab bits of light and create dark lines. Those dark lines we can measure using our spectrograph.

Fraser: So while the star is going strong, you won't be able to see the effect of the planet in the light.

Pamela: It's too hot to have a lot of lines to look at, and what lines you have to look at are spread out by how fast the thing is rotating.

Fraser: Now if you had a planet going around a star that was three times the mass of the Sun, would that be fun?

Pamela: As long as you move it out from the star, it's just fine. It's all a matter of placement. Where the Earth is in our system, we have liquid water. If you replaced our Sun with an A-type star we'd have boiling water (and that would be a kind of bad thing). If you replaced our Sun with an M-type star instead, then we'd freeze. So, where the appropriate place is varies with star. With an M-type star, you'd want to get in closer to where Mercury is. If you have an A-type star, you're going to want to move further out. So find your planet, put it in the appropriate location, and you can build a habitable zone for every star.
 
The other question is how long is that habitable zone a safe place to be? M stars… once you survive that first billion years or so, you're good for another 40 billion years. A-type star? Much shorter lived, so even compared to the Earth, you're just not going to have as much time to develop a civilisation before your sun starts doing things that just make life impossible.

Fraser: Right, but I guess it's just a new area of investigation, that up until now, astronomers didn't even think they could look at.

Pamela: No, and there are theorists out there who are making their living calculating where the habitable zone is for this type of star if you have this type of planet with this type of atmosphere and how long does that habitable zone stay there… it's really a fascinating question because you have to take into account so many different things, but we think we know what a lot of the things you have to plug into your models are. Now it's just a matter of writing the complicated software and getting enough time on the supercomputers.

Fraser: That was great Pamela, sounds like you had a lot of fun there.

Pamela: It was a really good meeting, and it was a smaller meeting than normal, so people took the time to sit down and really talk about what they had to say. There's very little that can be said about going to Hawaii that's negative. So, really – great location, people willing to sit down and talk, and it was just pleasant and fun and I learned a lot.

Fraser: So where's the next one at?

Pamela: The next meeting is in Austin, Texas, where I went to graduate school, and that one's going to probably not be so pleasant, but it's certain to be a lot of fun. Hopefully next time you'll be able to make it. The meeting after that is in St. Louis where I'm currently located.

Fraser: That'll be good. I'd love to. All right, we'll talk to you next week.

This transcript is not an exact match to the audio file. It has been edited for clarity.

]]> http://www.astronomycast.com/astronomy/episode-40-american-astronomical-society-meeting-may-2007/feed/ 1 Ep. 20: What We Learned from the American Astronomical Society http://www.astronomycast.com/astronomy/episode-20-what-we-learned-from-the-american-astronomical-society/ http://www.astronomycast.com/astronomy/episode-20-what-we-learned-from-the-american-astronomical-society/#comments Mon, 22 Jan 2007 16:14:41 +0000 Astronomy Cast http://www.astronomycast.com/interviews/episode-20-what-we-learned-from-the-american-astronomical-society/
Episode 20: What We Learned from the American Astronomical Society (12.6 MB)]]> Supernova remnant in infrared
It's astronomical society get together time, and we send Pamela to investigate and record. Hear the latest news that will make your text books out of date. Find out where all the dark matter is collecting, the identity of Kepler's supernova, and new insights into the closest, brightest supernova in recent memory.

Episode 20: What We Learned from the American Astronomical Society (12.6 MB)

Mapping Dark Matter in the Universe

Background information on key concepts

Kepler's Supernova Remnant

Background information

Luminous Blue Variable Stars

General information on LBVs and stellar evolution:

 
Download the transcript
 

Transcript: What We Learned From the American Astronomical Society

Fraser Cain: We've been sort of leading up to this, we've mentioned that we're going to do it, and now I think that we're ready. So, I think we're going to be able to let people hear some of the interviews you did at the American Astronomical Society.

Dr. Pamela Gay: That sounds like a great plan. I was able to talk to some really great people and learn about some areas of science that my own research never even touches on, and find out about things that are actually invalidating parts of the textbook I teach out of. It's always fun to be able to turn to my students and say 'Today I found out that your textbook is currently out of date."

Fraser: I think we've covered a lot of subjects, you know – from supernova, dark matter, dark energy – and this is all the latest stuff. I'm hoping that people have heard all the episodes, they'll be able to put it all into context and go "oh okay, I understand now from this point of view." I think all of the stuff we'll be talking about today, we've actually covered the basics in previous shows.

Pamela: And now we get to update and invalidate ourselves all at the same time.

Fraser: Perfect. So we're incorrect, out of date. So what's first?

Pamela: Well, the very first, really cool press conference at the meeting had a group from the COSMOS survey. COSMOS in this case is actually an acronym, for the Cosmic Evolution Survey. They used a bunch of telescopes – Hubble, XMM Newton, Spitzer, Keck, the Very Large Telescope in Chile, the Very Large Radio Telescope Array in New Mexico, and the Subaru telescope – just about every telescope on the planet it seemed like – to in detail measure the distribution of matter that we can see (luminous matter) and the distribution of dark matter. They had some really cool results that I was able to get Richard Massey, a post-doc in the project to describe straight for our listeners.

Fraser: All right, let's hear what he has to say.

Dr. Richard Massey: So what we've revealed in our map of the dark matter distribution is that it makes a filamentary structure, rather like a sponge. All the dark matter is distributed along a series of very long filaments, which meet in massive clumps of dark matter and surround enormous voids in space. This is absolutely vital in terms of the baryonic or ordinary matter, and helping it evolve into the forms we se around ourselves today.
 
It's vital in two ways. Firstly, the sheer amount of the stuff holds the universe together as it tries to expand away from the big bang. By its own gravity, it keeps everything compact and in places where it can go on to form galaxies and stars.
 
As a second point, the dark matter is also vital because it has a crucial lead-time over the ordinary matter in its gravitational collapse. From a smooth universe, at the big bang, which we see in the cosmic microwave background, this gradually transmissions into a more clumpy, filamentary distribution where the matter is more compactly represented in space.
 
So the dark matter, which begins this collapse first, therefore forms an underlying scaffold, which is absolutely vital for the baryonic matter, which can later flow into this scaffolding. It's very much like scaffolding, as you would build a house. The dark matter goes up first, around the outside, and then the baryons, which we know and understand, later flow into that scaffolding and are slowly, gradually, constructed into the galaxies, stars and planets that we find around ourselves today.

Pamela: Can you tell us anything about – are the peaks the same between the baryonic and dark matter or are there offsets? What new things have we learned about the distribution?

Dr. Richard Massey: So generally the distribution of the dark matter and baryonic matter are very strongly correlated. In other words where there's dark matter, in general, there's some baryonic matter. That's very much in line with the theoretical expectations that were made in advance of this new math. So overall it really provides a very strong confirmation of those theories, that we really understand what's going on, on large scales.
 
Having said that, there are a couple of discrepancies in the distribution of baryons and dark matter, so in some places there is dark matter and no baryons, and in others vice versa. Although fundamentally this map is really at the limits of image analysis techniques, it's really pushing the bounds of what we're able to measure, so it's slightly noisy. However, these (and I don't necessarily want to believe all of these discrepancies) offer really tantalizing glimpse into differences of behaviour of dark matter and normal matter that may provide a clue as to its nature.
 
So the first question we've answered is where it is. Answering what it is, these discrepancies might provide some insights by the different ways that they interact with each other and consequently the different places that they end up.

Pamela: Does this completely rule out, forever, the fact that gravity might have some additional modified term, or are you simply saying there has to be dark matter but gravity can still be modified?

Dr. Richard Massey: So this result, and others like it using this technique of gravitational lensing, now provide mounting evidence that there is definitely some sort of dark matter in the universe, some additional missing mass over the baryons that we can interact with, that we can see, breathe, feel and touch around us. There is definitely something else there.
 
Now, of course, this doesn't rule out the fact that there might be other theories of gravity that might also be true. So, these initial theories were brought in to explain theories mounting evident a couple of decades ago that there is missing matter in the universe. Now people suppose that either there is missing matter (and that therefore some of it is made up by dark matter), or perhaps that the theories of gravity are wrong. We have found that there is definitely missing mass, and definitely dark matter, but this doesn't say anything necessarily about the possibility that there might be both.

Fraser: Well, that was great! Good job on getting that interview! So what's the next piece of research that you were able to look into?

Pamela: Well, a little bit later in the conference they had basically what turned into a supernova round up of great explosive discoveries in our universe.
 
Dr. Stephen P. Reynolds from North Carolina State University presented on a supernova remnant that is near and dear to a lot of people: the Kepler supernova remnant. This is a large nebula that can be seen that was formed in an explosion that was observed by THE Kepler, the Kepler who figured out how planets move and all that sort of neat stuff. In studying this supernova, he found that our understanding of when the elements needed to form planets were released into the universe may be wrong, and our understanding of exactly what types of stars can become white dwarfs may also be wrong. He took the time to sit down and explain all of his research and all of its repercussions to our understanding right for our listeners.

Fraser: All right, well let's listen to this one!

Pamela: I'm here with Stephen Reynolds, a professor of physics at North Carolina State University. This morning he did a wonderful presentation on how type Ia supernovas aren't exactly everything we ever thought they were. Could you sum up your results for us?

Dr. Stephen Reynolds: Short answer is that the nearest supernova well observed from Earth in 1604 has left a remnant which seems to have characteristics of both a type Ia supernovae exploding white dwarfs and the single massive stars that leave their surroundings full of dense circumstellar material. Kepler's supernova remnant appears to be a type Ia supernova that also left behind lots of stuff, indicating perhaps that it's progenitor was perhaps more massive than the common, run-of-the-mill type Ia supernova.

Pamela: Now, this is a supernova that people have clearly known about since, well, Kepler was around. Why is it that it has taken so long for forensic astronomy to make a clear determination on the type of supernova that created this object?

Dr. Stephen Reynolds: It's useful to remember first that the whole idea of supernovae is only about 80 years old. The idea of type I and type II is about 50 years old. The realization that type I's were partly massive stars that had lost their hydrogen and partly exploding white dwarfs is only about 20 years old. So it's truly only been a puzzle for about 20-25 years. It's x-ray astronomy that helps you make the distinction and we've only had x-ray astronomy as well for about that long.
 
After that, why didn't we face up to it sooner? Well, it took a while to accumulate optical, x-ray and other kinds of information, so it's probably been a puzzle for about 10 years. The reason we didn't settle it sooner is because, well, scientists are conservative and most type Ia's don't seem to show this circumstellar material and so the conventional wisdom was if either it didn't have it, or if it had it, it wasn't a type Ia. So we've just been forced by the data to say, yes, it is a Ia.
 

Pamela: What were the lines of evidence that you used to clearly state, forever and always (we hope), that this is a type Ia supernova remnant?

Dr. Stephen Reynolds: We're very fortunate. An exploding massive star cooks lots of elements, but the densest ones wind up trapped in the neutron star left behind. The material that's ejected into space tends to have pretty well agreed upon patterns of heavy elements, for instance lots of oxygen and some iron (but not very much), whereas the exploding white dwarfs produce mostly iron, so that the ratio of oxygen to iron atoms is less than 1 for a type Ia. For a core collapse supernova, that ratio is predicted to be 70. Even astronomers should be able to tell the difference between 0.7 and 70, so that's what we did. We looked for the oxygen, which we couldn't find, we looked for the iron which was everywhere.

Pamela: Type Ia supernova – they're one of our standard candles that we use to measure the universe. If they aren't all exactly the same, what sort of evidence can we look for/inspect for to say that the ones we're using as standard candles are still trustworthy standard candles even though we have these other type Ia things that are slightly different?

Dr. Stephen Reynolds: Well, two answers to that. First one: the reason that Ia's have suddenly become so useful is because people realized that they weren't quite exactly the same –this was already realized. Purely observationally it was found starting in the early 90s, that the ones that were slightly brighter also lasted slightly longer – their light faded a little more slowly. Nobody knew why this was, exactly, they had some ideas but observationally, the brighter the slower, the faster the slightly dimmer. People were able to use that to correct a little bit, and it's that extra correction that gave us the leverage to learn the wonderful things that we've learned.
 
Now we don't know yet whether the actual explosion of a white dwarf that it originated from a more massive progenitor would be different, and if it obeyed this same relation – if it was brighter but also slower decaying then it's already taken care of. What would scare us is if it turned out to be radically different – that it was brighter but its decay rate mimicked a fainter one. Then we would really be in trouble because these would be the first type Ia's that the universe could produce, because their progenitors evolve faster and what you really don't want is a systematic effect with distance, so that the ones that seem to be furthest away that occurred the earliest are systematically different in a way that mimics a different kind of supernova.
 
What we're asserting is that the progenitor of that white dwarf, rather than being a star with maybe 2 solar masses, which could take a billion years from its birth to producing a white dwarf, might have had 6 or 7 solar masses – still not enough to become a core collapse supernova but enough to have evolved considerably faster and it would have to lose all that extra material (which we think happens), and that would be surrounding it. The white dwarf is still only 1.4 plus one atom mass, but its progenitor was more massive and rapidly evolving.
 
So basically, this is early days in this. We don't know whether we're learning about the mechanism for all Ia's and we just happen to have a system that is able to show us that better or if the explosion itself is characteristically different. We hope that if we find it's different, we will also find an imprint so that when we observe actual supernovae in distant galaxies, we'll say 'aha, this is one of these massive guys, we'll leave it out of the sample' we don't know yet what that signature might be or even if we'll need one.

Pamela: So what are you hoping to find to use to build on these results – perhaps some new explosions and what data do you need to better secure your result?

Dr. Stephen Reynolds: The first thing is, we have barely scratched the surface with this astonishing Kepler data set. We have 30 million x-ray photons each polished and cherished and focused to within a half-arc second by the splendid Chandra telescope, each of whose energy has been measured. We will be working for years just on analyzing Kepler's data and bringing it closer to the predictions of models.

Pamela: Well thank you very much Dr. Reynolds. Any parting words that you want to pass on to our audience?

Dr. Stephen Reynolds: Let me take the opportunity to point out one additional important feature of this. We live on a planet which is largely iron. It would be interesting to know how soon the universe could make iron. If a significant number of type Ia supernovae can live their lives out and explode in 100 million rather than 1 billion years, the universe started making heavy elements that could turn into planets and people ten times sooner than we thought. Next time you see a little green man, he might be older than you'd conceived.

Fraser: Great, alright – well that was good. Two down, what's the third one?

Pamela: Well, in that same press conference, a post-doc at the University of California, Berkeley, reported on these little blue stars (that in all reality are giant blue variables), that have nebula around them that looks suspiciously identical to the nebula that we find around the supernova remnant 1987a. He found that these blue stars, which we didn't think were likely to go supernova, just might be likely to go supernova. He talked to us about what this means to our understanding of stellar evolution.

Fraser: 1987a is the one that went off in the Magellan clouds, back in the—

Pamela: –Uh, Magellenic clouds

Fraser: Magellenic, right, sorry

Pamela: Named after Magellan, the explorer. Yeah, and it was the first supernova that we were able to get really good images prior to the supernova entirely by accident. We were imaging these nearby galaxies because they're nearby and easy to study, and this supernova went off, so we had all these images to go back and study what the star looked like right before the supernova. We built all these Rube Goldberg experiment-type theories to try and figure out how this star went supernova because it wasn't something we expected to explode. This new research by Dr. Smith and collaborators shows that maybe our initial understanding was wrong and maybe more stars than we ever imagined are capable of just exploding.

Fraser: Don't give everything away – let's hear what he has to say!

Pamela: Okay, here goes.
 
I'm here with Nathan Smith, a post-doc at the university of California Berkeley. He has some fascinating results that may just change our view of how giant stars end their lives, and may have some implications on Eta Carinae. So could you sum up your results for us?

Dr. Nathan Smith: What we've done is we've discovered a few new stars with circumstellar nebulae around them. This is material that is ejected before the star explodes and these nebulae look very similar to 1987a in terms of their geometry. They have a bi-polar geometry where they're ejecting material out of their poles but they also have an equatorial ring – a very prominent ring – and the similarity of these nebulae to the nebula that was around supernova 1987a has important implications about what that star might have been doing before it exploded. In particular it draws into question one of the prevailing models for how the 1987a circumstellar nebula might have formed and what that star might have been doing before it exploded.

Pamela: Can you tell us a little bit about what made 1987a such a unique and exciting case especially because it was so close?

Dr. Nathan Smith: Right, it was the nearest supernova in about 400 years that had been well observed. This wonderful data that we were able to obtain for 1987a showed more detail and it was the best-observed supernova ever. What we've learned from that is that we have data that existed before the supernova went off, and this had never been seen before with any kind of supernova. Astronomers were able to identify the star in images before it exploded that were taken a decade before. It was found that it was a blue supergiant, which contradicted most of the common wisdom at the time that a star should reach the stage of a red supergiant and then explode.

Pamela: Now, as some of our listeners may remember, in an earlier episode we discussed how supernovae come to happen. We discussed that stars like Eta Carinae end their lives as these giant stars that suddenly start blowing off these really hot winds as a Wolf-Rayet star and then they finally basically explode in their final death throes. Now, this was a star that under normal models would have gone through that phase, but now you're saying that they're basically exploding much earlier and not going through that phase. What implications does this have on our understanding of stellar evolution for these giant stars?

Dr. Nathan Smith: : These other objects we've discovered are – at least one of them is known to be a luminous blue variable and the other ones may be going through a phase that is analogous to it.
 
First of all the nebula that are ejected are formed during this LBV phase and must be formed in a different way than had been proposed for supernova 1987a, which required transition through a red supergiant phase to a blue supergiant. It had to involve a merger to spin up the star to create this kind of geometry. Now we're seeing these other stars do that without this mechanism, without a merger, without passing through a red supergiant phase. The similarity of their nebulae to 1987a suggests that they may also be poised to explode; they might be in the final throes of their life. That suggests that we could be looking to these stars, the luminous blue variables, as possible progenitors of supernovae and the reason that is something new is because when we study the chemical abundances of the nebulae around LBVs and we think about their place in stellar evolution which is supposed to be at the end of core-hydrogen burning (which is the first stage of burning), and not yet at the more advanced stages which are required before the star can suffer a core-collapse. This means that if they do potentially explode that means that they're blowing up much sooner than we thought.

Pamela: Does this imply that the opportunity that someone alive today just might observe a supernova in the nearby universe has now gone up?

Dr. Nathan Smith: You mean for Eta Carina? I'm certainly hoping so at that. I'm planning on that one exploding near the end of my career.

[laughter]

Pamela: So we no longer have to wait for Eta Carina to become a Wolf-Rayet star, it just might go. Now these other stars that you're observing, are they also in the "they just might go" category?

Dr. Nathan Smith: The thing is we just don't know. The evolution of these massive stars is still very uncertain because they span a wide range of masses and are very rare, so we only have a few examples with which to try and piece together the complete picture and it's very difficult.
 
It doesn't just depend on the initial mass, it also depends on the rotation rate, it depends on the chemical abundances when the star was born, and it can depend on whether or not there was a companion star. All these variables figure into the equation in different ways. It may be the case that even two stars that start in life with the same mass, because of these other properties – different rotation rates, chemical abundances – might have end phases that are different. In other words a star with the initial mass that would normally reach a Wolf-Rayet phase after the luminous blue variable phase may not get there. So two stars in the same place in the H-R Diagram (which tells us about stellar evolution), two stars that look the same, one might blow and the other one might have to wait another 100,000 years.

Pamela: With all these things you're finding with these very surprising objects, what is the thing that has startled you the most in this discovery?

Dr. Nathan Smith: I guess it's the variety of the different possible end states of these stars. It's so phenomenally complicated, or it at least seems that way maybe because there are so few examples. As we continue to study these objects, we get more and more examples of them.
 
In another part that's related to that, the variety maybe comes by how fast transition has happened. For Eta Carina for example, when we've looked at the chemical abundances of material further away from the star, we see that the chemical abundances have changed. The pattern of the chemical abundances that have been ejected in the last 1,000 years have gone from normal composition like our sun to something that is very enriched in Nitrogen, so these things can change very fast. It's giving us clues that maybe the normal pictures of slowly transitioning from one stage to the next are not the norm, but maybe the episodic mass ejections may be more than the norm.

Pamela: Thanks a lot for spending the time talking to us, Nathan. Do you have anything that, in summary, you'd like to say out to our audience?

Dr. Nathan Smith: I guess we should keep an eye on some of these massive stars, because if some of these close by ones do go off, they're going to be spectacular events. If they're in the northern hemisphere, there are a few of these objects we've discovered if they do explode as supernovae, they'll be the brightest thing we've seen in a long time, so it's something to keep a look out for.

Pamela: But we here on Earth are in absolutely no danger, because they're all more than the n parsecs that you have to worry about.

Dr. Nathan Smith: I wouldn't say that necessarily. Eta Carinae is only 2 kilo-parsecs away, and if it were to explode in a very energetic supernova, something like a hypernova, we're probably going to be safe. Likely what would happen is that the x-ray blast from the supernova might disable all of our satellites. This happened recently with some coronal mass ejections from the sun, and if some satellites were disrupted with x-rays, this explosion would actually have a serious effect on our communications. If we were unlucky enough to have the pole of the star aimed at us in a gamma-ray burst or type event, some people have suggested that type of event may periodically cause mass extinctions on Earth. Whether or not that's true is debatable and luckily though it looks like Eta Carinae's pole is not aimed at us, so we're probably safe.

Pamela: So, humans are safe. Our atmosphere protects us from the UV, but lord help all the satellites in orbit?

[laughter]

Dr. Nathan Smith: Something like that, yeah

Pamela: Thanks a lot, Nathan. It's been great talking with you.

Dr. Nathan Smith: Great, thanks.

Fraser: Okay, great work Pamela! Thanks for getting out there and putting the microphone in people's face and getting the research right from them.

Pamela: It was my pleasure. It's really fun to get to talk to people about what they're doing, instead of just reading what they're doing in journal articles.

Fraser: Now next week, as we kind of threatened a couple of weeks ago, we're going to do the repercussions of the black hole episode. As predicted, our mailbox is filled up with questions about black holes, both clarifications and what-if's. I think we'll try and queue up a bunch of those for next week and get through them. You ready for that?

Pamela: I'm going to try and be ready for that!

Fraser: There are some pretty interesting questions

[laughter]

Fraser: Black holes always make people scratch their heads, so that will be good.

This transcript is not an exact match to the audio file. It has been edited for clarity.

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