Dr. Fraser Cain: This wasn’t our intention but we’re actually coming up with another series.  We talked about the Sun last time and we’re going to talk about the Sun today and maybe we’ll talk about the Sun next week.  I don’t really know.  

Dr. Pamela Gay: We just have too many big ideas that refuse to be confined to 30 minutes.

Fraser:  I know.  This could be one show, this could be two shows, I don’t really know.

Pamela: We’ll see where we go.

Fraser:  Exactly, we’ll just let the show decide.  We’ve talked about the Sun before.  This time we’re going to look at the entire life cycle of the Sun and all the stages it’s going to go through, Solar Nebula, Protostar, Main Sequence, Red Giant, White Dwarf and more.  So if you want to know what the past held and what the future holds for the Sun get ready for the grim details.  [Laughter] And of course this will always end on a sad note.  

Okay Pamela, I think the goal here today is to go through in excruciating detail all of the stages of the Sun.  It is actually really amazing all the crazy stuff that happens.  So let’s rewind time all the way back to 4.6 billion years ago plus plus and talk about what came first. 

Pamela: Well, once upon a time there was nothing more than a giant cloud of gas and dust.  That’s the boring part.  We don’t know how long that cloud of gas and dust just sorta hung out doing nothing other than maybe glowing faintly.  Somewhere along the line that cloud of gas and dust was caused to contract; caused to fragment and turn itself into a bunch of baby Stars.

Fraser:  Now the key is that it was a cold cloud, right?

Pamela: Yes.

Fraser:  And not a hot cloud.  If you get a hot cloud of gas it will never contract.  

Pamela: This is because temperatures related to the rate at which Particles are flying around.  If you have something hot the Particles are bouncing around, bouncing off of each other and it’s hard to get that to collapse down because you have this thermal pressure holding the cloud apart basically.  

But if you have cold gas and dust that is just hanging out in Space and you whack it, it will start to condense.  As the gas and dust fills a smaller and smaller volume, Gravity will start to drive that contraction faster.  

We talk about the point at which something starts to identify itself as being the beginnings of a Star as the Hayashi track.  With a Star like our Sun, it actually started out about ten times brighter than it is right now as it started to contract off of this Hayashi track. 

So for several million years, we’re not exactly sure how long this process takes, the Sun contracted and actually got fainter as it contracted and then started nuclear burning in its core.

Fraser:  So before it was bright but it wasn’t burning with nuclear fusion in its core?

Pamela: No, it was actually all thermal heat.   This is sort of what Jupiter is doing.  Jupiter actually gives off more light than it is simply reflecting from the Sun.  If you turned the Sun off, Jupiter would still be giving off light.  

This is because gas that is being held together, being pushed together, being squished together by Gravity actually emits thermal radiation for many billions of years.

Fraser:  Right so the first few million years of the Sun, it was just a ball of Hydrogen and Helium held together by the Gravity and just headed up by that process.  No fusion necessary.

Pamela: The best way to think of this is it’s the opposite of spray air.  When you spray your hand with spray air, it’s really cold because the gas is expanding.  In this case we’re squishing the gas together and it’s heating up.  So, gas squished, heated up and eventually it starts nuclear burning.  

This process probably started with Deuterium burning.  This is where you’re burning up bits of Hydrogen Atoms that have an extra Neutron in them.  These actually burn a lot easier than just regular run of the mill Hydrogen.

Fraser:  And where did those come from?

Pamela: Those probably came from the Big Bang.  So we’re burning up the building blocks of the Universe basically.

Fraser:  The point being that it’s like at early enough on you didn’t have the conditions to fuse Hydrogen yet, but you still had a few left over chunks of Deuterium and those could start to fuse together.

Pamela: Eventually you do end up with nice friendly Hydrogen burning in the center of the Sun.  Over the process of getting to that stage the Sun first overheats a little bit and then cools down to settle into a nice friendly what we call main sequence life.  This is the first big main part of saying that is a Star.  

So we go from protostar which is the process of going off of the Hayashi track to contracting to just settling down into nice round Star that has also along the way blasted everything out from around it.  

During the early parts of the Sun’s life, they go through many radical stages with lots of x-ray flares, lots of high energy output.  They go through their own form of “the terrible twos” that includes High Energy Radiation. 

Fraser:  Now why are they so violent and active at that stage?

Pamela: As they collapse there’s material streaming on to them.  Our Solar System is basically an Accretion Disk at this point, a disk of material where some of that material is just streaming on to the Star in the center.  

You have powerful Magnetic Fields in many cases.  You can have jets coming off of the poles of the Star.  All of these different interactions can lead to flares as the Star settles down.  

Fraser:  So it’s almost like new chunks of material are landing on the Star and that causes flares.  It wasn’t that inflow of material that causes the Star to settle down.

Pamela: We also don’t know exactly what the details of the Magnetic Field evolution at this point is because you have all these Magnetic Field lines that are rearranging themselves as well.  There is lots of potential for badness to be going on.

Fraser:  Now the Sun has finally settled down to its Main Sequence.  But that was like four and a half billion years ago, right?

Pamela: So depending on what paper you read, the protostar stage could have taken hundreds of thousands of years or a few million years.  That’s a short stage to get nice solid Star formation going on and to get our Planets formed and to get everything lined up so that we have a Solar System that looked like the Solar System we live in today although the terrestrial surfaces were very different.  The pieces were all there.

Fraser:  Right, but how does the Sun look?  We’re still on a Main Sequence phase, how does the Sun look different when it started the Main Sequence to where it is today?

Pamela: Its temperature has changed slightly.  It was a little bit hotter in the past – our Sun has actually cooled off some over the years.  Once it hits the Main Sequence Stage, it’s a fairly constant Sun.  We’ve had a bit of cooling off but our Planets found other ways through gases and stuff to keep going in a way that works for us.

Fraser:  But how is it changing – even though it’s in the Main Sequence – it must be changing a little bit, right?  Hydrogen is getting fused into Helium.  

Pamela: There are long term changes in temperature.  Over time our Sun is now heating up again. So we went from being hotter and the Sun cooled off and now slowly we’re getting warmer and warmer over time.  It’s a gradual enough process that even over those 5 billion years; terrestrial effects have been really what have dominated the situation here on the planet Earth.

Fraser:  Okay so the Sun is getting hotter – we’re not talking like a cause for global warming – we’re talking billions of years.  

Pamela: Right, so it’s only in like 50 million years from now that we’re going to have to start worrying about the temperature has gone up enough that it starts to affect the planet Earth.  

If you look at people who look at long term cycles in the Sun, there are a lot of them who believe for a variety of reasons that are hidden in the field of Solar Astronomy, that our Sun is actually in the process of a cooling period that has to do with how the Magnetic Field is evolving over time.  There’s lots of long term and short term changes in the Sun’s behavior.  

We think that there is currently a short term slight cooling phase going on but that’s superimposed over a long term heating of the Sun that about 50 million years from now is going to start to impact us.  The Sun actually will stay a Main Sequence Star for probably another 5 billion years.

Fraser:  Right, so we’re only not even halfway through the process yet.

Pamela:  It’s middle-aged still though because the periods that come after it are so short that we can start to look at ourselves as being in our mid-40s if you are talking about someone who lives to be 100. 

Fraser:  Then I guess at some point – we’ve talked about this before – that the heat from the Sun is going to start to really impact our Planet, right?

Pamela: Yeah.  This is where we start having our oceans heating up.  That leads to higher humidity in the air which leads to the Planet heating up more which of course heats the oceans more and eventually the oceans evaporate – total runaway Greenhouse Effect.  No more life on Planet Earth.  It’s rather depressing but our Universe is after all trying to kill us.  [Laughter]

Fraser:  We’ve covered that before.  [Laughter] I’ve seen some competing series on this but essentially 500 million to a billion years from now there will be no liquid water.  Water vapor will have boiled off into Space.  We’ll essentially be very much like Venus, just a little cooler.

Pamela: Yeah.  

Fraser:  We’re on our way to Venus.  So, Earth doesn’t matter anymore.  [Laughter] The Sun is still a concern.  That’s still like 3 billion years from now.  So when do things get interesting again?

Pamela: About 5 billion years from now we start to run out of Hydrogen that is readily available for fusing in the center of the Sun.  When this happens the Sun is going to start contracting because there is not going to be as much pressure from the light supporting the outer layers of the Star.

Fraser:  This is kinda interesting because even though there is tons and tons of Hydrogen in the whole Sun and if you could somehow mix it all back up again – give it a stir – the Sun could just go on for hundreds of billions of years, right?

Pamela: This is what happens in little tiny tiny Stars.  The burning process is able to create what we call convective mixing.  The entire Star essentially acts like a Lava Lamp.  It’s able to constantly refuel the center of the Star.  

As you get to bigger and bigger Stars like our Sun, you reach the point where that mixing no longer takes place.  So as you’re burning Hydrogen into heavier elements in the center of the Sun, those heavy elements stay there.  You end up building up a Helium core to our Sun.  

Once the core is exhausted of its Hydrogen fuel the Sun will begin to collapse and it will reach the point where a shell of Hydrogen around that Helium core is able to ignite. The densities around the core get high enough and the temperatures get hot enough just from the weight of everything resting on them that we burn a shell of Hydrogen.  

At this point we talk about the Sun being off the Main Sequence and the next really interesting phase starts to occur once you reach the stage that you get a Helium Flash.  For awhile you have what we call a Red Giant Branch Star.  This is where you’re burning the shell of Hydrogen but the Star is still collapsing.  

The Sun is still getting smaller and smaller and the center of the Sun is getting hotter and hotter under the weight of this collapsing material above it.  The pressures are getting higher as everything is getting confined into a smaller and smaller area.  

In a magical moment when it reaches a temperature ten to the 8 degrees, suddenly the Helium in the center of the Sun is able to ignite.  We call this a Helium Flash.  At this point the Sun becomes what we call a Horizontal Branch Star.  Now you have a new segment in the evolution of the Sun.  This phase can also be called the sub-giant phase of the Star.  Here you have the Star happily burning Helium, it bloats itself back out. It gets hotter in the core once you get this new burning going on.  You get more light pressure supporting the outer layers of the Star, Star bloats out.  It also drops in luminosity here.  

This is one of the neat trade-offs that is happening with the Star. It’s constantly changing every so slightly in brightness and in temperature as it goes through all these different phases.  So once the Hydrogen shot off, the Star got much redder. Now that you have the Helium burning, the Star gets a little bit bluer again and that’s kind of cool.  Eventually the Helium also exhausts itself in the center of the Sun.  

All of the Helium ends up burning itself out into Carbon.  Here again you end up with shell burning.  So now you have this Carbon core surrounded by a shell of Helium that’s burning itself surrounded by a shell of Hydrogen that’s burning.  So you start getting Onion15:11 of Sun.  This is where we talk about the Star being a Red Giant again.  Exactly what happens depends a little bit on metalisty15:19 of the Star. 

In a lot of cases as it goes through these phases we can also end up with it being what’s called a Variable Star where it pulsates in brightness.  This happens to Stars that are just like our Sun.  They can go through a phase of pulsations as they go along.  As they start running out of all this fuel, this is where we call them Mira Variables.  They’re giant, they’re bloated; the outermost layers of the Star are thinner than the Earth’s atmosphere which is kind of cool to think about.  

This is where you start to spread our Sun out over a volume that just fits – maybe we think – within the Earth’s Orbit.  We don’t know for certain.  And you also start getting Mass loss in Space as the nuclear burning is going on. The outer layers of the Atmosphere have expanded out so far that sometimes just a slight push from the core of the Star which is sputtering as it burns is able to cause puffs of the Atmosphere to drift away.  

Fraser:  And the red color is just coming from it being cooler, am I right?  Back in the olden days the Sun was white because it was a temperature of nearly 6000 degrees Kelvin and now it’s cooled down even though it’s a lot larger, right?

Pamela: So here we’re starting to get down to 4000 degrees Kelvin. This change in temperature is enough to change its color so that it’s a deep red.  

Fraser:  But the overall brightness of the Sun is way higher.

Pamela: This is because you have a much larger surface area that the light is going through.  Each bit of that surface area is able to radiate away Photons and all those Photons add up to being a much brighter Star.  

Fraser:  So even though the Sun is changed to red, it’s now visible from a much further distance than it was before.

Pamela: This is part of why so many of the really bright Stars that we see in the Sky are these red Stars.  We can just see red Stars at a much greater distance and this is a common phase for Stars to go through.  What’s kind of amazing is the time scales that all of this has been happening on.

Fraser:  That’s just what I was going to ask – how long does this last?

Pamela: Our Sun hangs out on the Main Sequence for a few billion years – like 10ish billion years.  Then it only spends a few hundred millions years going through all the rest of the stages.  So those are relatively short stages in a Star’s life.  

We refer to the Main Sequence as the majority of the Star’s life and that’s exactly what it is.  Then it goes off and does all these really cool things but those happen essentially in the blink of a Cosmic eye.  Once the Star hits the Mira phase, just maybe four or five hundred million years after leaving the Main Sequence, at that point it starts losing its Atmosphere.  

It starts transitioning from being a Star that’s burning and doing all the Star-like things to blasting its Atmosphere away starting to form a Planetary Nebula.  A Planetary Nebula is nothing more than the Atmosphere of a Star that’s been exhaled and hasn’t yet drifted so far away from its starting point that we can no longer see all the gas associated with one another.

Fraser:  What’s the mechanism that actually gets the Atmosphere away from the Sun?  Like what’s blowing it away?

Pamela: It’s the flickering and sputtering of these shells of burning Hydrogen and Helium.  As the Star collapses down you’ll get a burst of extra light that pushes things away.  The Star is so big that Gravity and Light are just barely in balance and it’s very easy to overcome that Gravity of the outer layers of the Star.

Fraser:  You almost get it kicking as it’s normally in balance and then it maybe sputters and gets brighter and more light pressure per second and then contracts but it’s enough of a push to shove off that outside layer.

Pamela: There’s also this constant Solar Wind that’s going out where you have this light pressure pushing out and it’s always able to remove some amount of the Star’s Mass.  We’re just not entirely sure how much of the Star’s Mass.  

What’s really amazing is we’re now able to start looking at detailed maps of the environments around some of these Stars and see all sorts of crazy strange structures that have formed during Planetary Nebula phases.  We don’t understand what causes all of these different strange shapes.  

There is different Planetary Nebula that looks like a series of nested boxes, a series of nested rings, figure eights and all of these are coming from fairly similar parent objects.  But there’s something that is causing it to look radically different in just how the Atmospheres were lost to form these Nebula.  

Fraser:  Magnetic Fields. 

Pamela: [Laughter] That’s the thing we always blame.  

Fraser:  Okay, so now our Sun is in this Mira phase, puffing off outside layers into Space….

Pamela: Eventually it reaches the point where between Mass loss and just burning up what little fuel it has, it starts to run out of Energy.  The Helium burning shuts down.  The Hydrogen burning shuts down.  And the last of the Atmosphere just drifts away.  

At this point you now have a hot cinder of a Star.  That cinder of a Star collapses down.  It no longer has any burning going on to support the Atoms against one another.  As they collapse they actually reach a degenerate gas phase.  This is where the Hydrogen and Helium Atoms pack themselves so closely together that the only way the Electrons can still exist is if they basically form a Matrix.  

You end up with Stars that their internal structure is essentially a diamond of Carbon surrounded by these extremely dense – we call them degenerate layers – of Hydrogen and Helium as well.  These are our White Dwarf Stars.

Fraser:  Right and so you’ve gotten a situation where the Gravity is so intense that it’s packing the Carbon and the Helium and all that’s left into a sphere but there isn’t enough Gravity to actually ignite fusion of the Carbon.

Pamela: In the process of packing everything together it gets so close that the pressure of the Electrons one against the other going: “no, you have the same charge as I do stay away,” and the poly-exclusion principle that are working to support the Star.  

If you made White Dwarfs any heavier you’d be able to overcome this and you’d squish everything down into being a Neutron Star which we will get to in a couple more episodes.  

But the remnants of Stars like our Sun are supported not by light but by Electron pressure.  That’s kind of neat to think of Electrons supporting a star.  These are the largest diamonds we have in the Universe.

Fraser:  Is it actually a diamond?  

Pamela: Yeah, it just might be.  If you think about it, what a diamond is. It is nothing more than Carbon Atoms that have been arranged in a Matrix which is one of the tightest structures that you can get those Carbon Atoms into.  That’s why diamonds are so hard.  

As you’re creating a White Dwarf you have to pack those Carbon Atoms down into a crystalline structure.  That’s where you start getting something that is basically nothing more than a really HOT diamond.  

Fraser:  Right, if you could cool it down and survive the Gravity and chop pieces off you could turn them into diamond rings. [Laughter] 

Pamela: Yes.  You would have to wait a long time for them to cool off though.

Fraser:  I’m a patient man. It’s a new business.  Anyone want to go into business with me [Laughter] in the Inter-stellar diamonds?

Pamela: You want your one Solar Mass diamond, don’t you?

Fraser:  Yeah, exactly.  So then, but it’s not dead yet, right?

Pamela: It’s still radiating heat.  It’s still hot.  This is the situation of Captain Kirk heats up the rock with his phaser and it takes a little while for the rock to cool down.  Well, White Dwarfs are a lot bigger than that rock and it takes them millions of years to cool off.  

Fraser:  Billions, trillions….

Pamela: It depends on how cool you want to get them.  So they’re cooling off over time and as these White Dwarfs cool off, the Planetary Nebula they sit in the center of also fades away as it expands away.  You’re essentially watching the home of the Star disappear.  

Its Atmosphere is dispersing moving further and further away from that Core White Dwarf.  The Star itself is getting cooler and as it is getting cooler it’s getting fainter and fainter.  

Eventually you end up with that gas and dust in the Planetary Nebula just sort of mixes itself in with the rest of the Cosmos.  The White Dwarf over billions of years cools off to the temperature of Space.  It’s a kinda sad future.

Fraser:  Right and we call that a Black Dwarf, right?  

Pamela: Yeah, it depends on who you talk to.  People are kind of nervous about using the phrase Black Dwarf because too many people mix it up with Black Hole, but that is one of the terms kicking around.

Fraser:  It there some super Scientific term?

Pamela: No.

Fraser:  Okay, some kind of degenerate …..

Pamela: Cold White Dwarf also works.

Fraser:  A Cold White Dwarf, okay.  That’s very scientific sounding. [Laughter] Now what do we see?  If we look out into the Universe, how far along that do we see White Dwarfs?  Are there White Dwarfs that are just now too cool for us to be able to see them?  Too cool for school?  [Laughter] 

Pamela: We don’t think so.  The Universe hasn’t quite been around that long.  One of the neat things that’s happening is we can look out at Globular Clusters, packages of in some case thousands of Stars, that are gravitationally bound together and are orbiting our Milky Way Galaxy.  These are some of the oldest objects that we know of, formed 13 or 14 billion years ago depending on whose Stellar Evolution Models you believe.  

When we look at them – we can use Hubble Space Telescope to probe fainter and fainter until we start to pull out the White Dwarfs – we can actually see what we call the White Dwarf cooling sequence.  

This is where you see a sequence of Stars in a plot of temperature vs. brightness that forms a nice polite line where the brighter ones are also bluer and the fainter ones are also redder.  There is a direct relationship between how bright they are and what temperature they are forming a perfectly straight line.  We can see where we stop getting Stars.  

This is part of how we come up with the age of these Globular Clusters is we know, okay the first Stars to be able to form White Dwarfs were Foo and they burned through their stuff fairly quickly because they were higher Mass, had large amounts of Mass loss and eventually ended up dying with only 1.4ish Solar Masses of material after all of their Mass loss.  

Then they collapsed down into White Dwarfs.  And then Stars that were a little bit less massive collapsed down to White Dwarfs.  And then Stars that were even less massive collapsed down to White Dwarfs.  The Stars that became White Dwarfs later are still hotter than the ones that formed first which are still cooler.  There aren’t any that have had time to reach the point that they’re too cool for school as you put it.  

Fraser:  Right, so you can look at a cluster, count up the number of White Dwarfs count up the number of Stars and get a sense of how old that cluster is.  

Pamela:  This is one of the many ways that we work to confirm the ages of systems.

Fraser:  Right.  Now is there going to be any time then – I mean the Sun is going to be slowly cooling down – is there anything left?  Will there be some time down the road where maybe Jupiter crashes into the Sun?  [Laughter] You know the White Dwarf Sun and you get re-ignition? 

Pamela: No, probably not.  It just doesn’t have quite enough Mass to do anything quite that exciting.  One of the interesting questions is going to be what happens as the Sun loses Mass through it’s – we call it the Asymptotic Giant Branch Phase – that period of time where it’s essentially a Mira variable.  It’s going to be undergoing huge amounts of Mass loss as the Mass leaves the Atmosphere and starts to form another Planetary Nebula.  

As that Mass is lost – first of all, it’s blasting the Planets – but second of all that Mass is no longer holding the Planets in their present orbits.  This is going to cause the Earth’s orbit to get bigger; the Mars orbit to get bigger; Jupiter & Saturn’s orbits to get bigger. It rearranges our entire Solar System.  

This is part of why we think the Sun isn’t actually going to consume the Planet Earth.  Earth will drift out of range.  So, our orbit will get consumed, but our orbit is just an artificial line around the Sun. Our Planet itself will probably escape.

Fraser:  I think you’re wrong.

Pamela: Why do you think I’m wrong?

Fraser:  The latest article I read:  “The Earth will be destroyed.  The Earth won’t be destroyed.”  I think the last article that we did was the Earth will be destroyed.

Pamela: See, I like the Mass loss people.  I’m a firm believer in Mass loss.

Fraser:  Well, no the Mass loss will still happen it’s just that it won’t be enough the Earth will still be destroyed.  Anyway, that’s the current thinking.  [Laughter] We’ll talk in a year and the current thinking will be:  Earth will survive.  

Pamela: Well, and you know, I’m sure that for every paper written on Earth will be destroyed, an equal number are being written at the exact same rate for Earth will not be destroyed. This is one of the areas of Science that we’re still struggling to understand.  We still don’t know how to calculate Mass loss halfway accurately.  We’re trying to figure it out but it’s a complicated process where you have to understand in detail how Energy is transported through the Sun.  

It’s a crazy situation where part of the Sun acts like a lava lamp with convection; other parts act more like light bulbs heating up the levels above them through radiative transfer and trying to figure out how all these things happen and how they change as the temperature of the Sun changes.  

It’s a really complicated process and we’re just starting to get computer software that is sophisticated enough to answer a lot of these questions.  We’re finally starting to get computers that are sophisticated enough to run that software without having to wait a few years for the answer.

Fraser:  Right we can just keep coming back and forth with the controversy then.  Five years more of AstronomyCast [Laughter] and you know, we’ll have flipped the position five times.  I think that’s the wonderful thing about Science you know, that it isn’t known. More evidence keeps getting brought to the table and the situation just keeps changing back and forth as more evidence is brought in.  

As more evidence is thought through and argued and that’s Science and I love that it’s how that all works.  It’s different like should you drink red wine or not? [Laughter] It’s like where you’re changing your drinking habits the fate of the Sun doesn’t really play into the day-to-day habits that I have.  

Pamela: It’s fun to watch how Scientists in general – a lot of us are willing to go yeah we’re not sure what the answer is but I’m going to go with this one because I like it – until we have more solid Science.  

When I first started studying Astronomy in college we didn’t know what the expansion rate of the Universe was and the choice was 50 or 100.  It was often: “Children use 100, it makes the math easier.”  [Laughter] We now know it’s around 70 kilometers per second per mega parsec.  But I’ll never forget that: “Children use 100, it makes the math easier.” 

Fraser:  Even though it’s completely wrong, could be off by you know…

Pamela: But we didn’t know if it was 50 or 100 and there were people fighting to the death over those two numbers and it turns it was halfway in-between.  

Fraser:  Alright, well I think next week we wanted to look at Stars that are smaller and Stars that are bigger.  The way those events unfold change dramatically depending on the Mass of the Star that you’re dealing with.  

So we’ll probably go through that whole process again but there’s things that will get a lot more exciting and a lot more boring; mostly more exciting.

Pamela: But there will be explosions involved.

Fraser:  There will be.  Okay we’ll talk to you next week.  

Astronomy Cast Episode 107:

Nucleosynthesis: Elements from Stars

Fraser Cain:  I hope everyone by now has heard our little surprise for the feed, which is that we’ve doubled the amount of Astronomy Casts.  So if you like that great, if you don’t like that, let us know.  Hopefully we can grind through more of your questions, which really feels great.  I actually really enjoy doing the shows and I really enjoy listening to them. I don’t know why. I think it’s just some of the cooler concepts come through the questions.  

Dr. Pamela Gay: Yeah, you guys ask way harder questions than Fraser does.  

Fraser:  I know I feel like I should just pass the microphone over. [Laughter] Okay, everyone here it’s your turn.  We’re done with our tour through the basic Forces of the Universe and so now we wanted to get back to some regular Astronomy.  Nothing too complicated this time around.

Pamela: Well that depends on who you talk to.  I think our talk is fairly complicated. 

Fraser:  All right then, fine.  Something super complicated.  Let’s get on to it.  So look around you.  Breathe in some air.  Everything you can see and feel was formed in a Star.  

Today we’ll examine the long journey that Matter has gone through, forged and re-forged in the hearts of Stars.  In fact, the device you’re using to listen to this pod cast has some elements formed in a Super Nova explosion.  

Just think about that.  I’m sitting here sorta spinning my wedding ring around and thinking it came out of a Super Nova.  

Okay Pamela, today we’re going to talk about how all of the Matter in the Universe came in one form or another, either from the Big Bang or from Stars or from Super Nova.  I guess at the end it’s all sort of the same environment.  

I think before we can do that I think it’s important for us to go into what are the Elements and why are they different?  How do you know what’s different from one Element to another?  What differentiates them?

Pamela: It all comes down to Proton and Neutron number at the end of the day.  The number of Protons tells you what type of Element it is.  So, you have Hydrogen with one Proton; Helium with two Protons and you build your way up through the Periodic Table adding more and more Protons.  

But the thing is there’s also this thing called a Neutron.  Some Atoms in order to be stable have to have both Protons and Neutrons in the core.  You end up with things like Helium-4 which is a Helium Atom which is number 2 on the Periodic Table. That 4 means that it has four bits, two Protons and two Neutrons sitting in its Nucleus.  Helium-4 is like one of the most stable things that you get.  

Then we build our way up through the Periodic Table creating heavier and heavier things through different types of processes.  In some cases we just add a Proton and it grows.  In other cases we add a bunch of Neutrons and these Neutrons decide to flip what they are between Protons decaying through a process called the Reverse Beta Decay.  

This is where the Weak Force gets involved and switches the identity of a Neutron into a Proton while emitting bits of other stuff like an Electron and the anti-Electron Neutrino.  

Fraser:  Then what is the definition of an Element?  It’s the Protons?

Pamela: It’s strictly based off the Protons.

Fraser:  Okay so one Proton is Hydrogen.  Two Protons is Helium.  Three Protons is Lithium, etc.  So, that’s where you go up with the numbers.  Whenever you see Gold or Lead, the first number is the number of Protons and if you add another Proton, you have a new Element, right?  
Pamela: That’s exactly what’s going on.

Fraser:  But then the Neutron, that’s where you get that number.  Like you say if it’s Carbon-14 you’ve heard about Carbon-14 Dating, that’s where the total number of Protons and Neutrons add up to 14.

Pamela: And in the case of Carbon you start off with 6 Protons and then to get up to that 14, you add 8 Neutrons to it.

Fraser:  Then those Neutrons can decay you could have six Protons and seven Neutrons and you’d still have Carbon but it just would be different in the number of total little balls at the middle.

Pamela: Yeah, that’s right.  So, when we talk about Atoms we often use the Periodic Table to figure out how many Protons there are, but in our shortcut language we’ll say things like Lithium-7 where Lithium has 3 Protons in it and Lithium-7 has 3 Protons and an additional 4 Neutrons.  

Fraser:  Then all of the things we’re going to be talking about today are the process of adding more Protons or Neutrons, right?  The point being is changing one Element to a different Element through adding Protons.  

So taking 2 Elements, mashing them together and you get something that is heavier that has more Protons.  It has new characteristics.  So, then the most common Element in the entire Universe is Hydrogen.  

Pamela: And that’s really nothing more than like a Proton by itself that decided to get a friend for an Electron.

Fraser:  Okay and where did that all come from?

Pamela: It came from Energy.  [Laughter] When the Universe first formed we were all Energy.  As the Universe cooled and got less dense, eventually that Energy was able to solidify out into Protons.

Fraser:  This is almost like the discussion we had about the Large Hadron Collider.  The whole Universe, the Big Bang was like a great big Particle Accelerator that turned (to borrow one of your words Pamela) ginormous amount of Energy into Matter.

Pamela: The Big Bang was sorta the biggest Energy-creating moment of all time and it ended up leading to all the Matter we know.  Originally, all that Matter was just pure Protons and pure Electrons that were happily bouncing off of one another and interacting wildly.

Fraser:  Would that have been Hydrogen at that point or just Protons?

Pamela: There you’re starting to get down to sticky names.  A fully ionized Hydrogen Atom is a Proton.  There is Ionized Hydrogen, Proton – same thing.  

Fraser:  So it is Protons without Electrons.  So it’s Hydrogen without Electrons.

Pamela: Pure raw Protons running around the Universe.  

Fraser:  So, then what happened?  

Pamela: As the Universe cooled about 100 seconds after the Big Bang, we got to the point that the density and the temperature of the Universe kind of resembled the inside of the Sun.  In fact it pretty much exactly resembled the inside of the Sun and we’re able to get these Protons colliding together and in some cases sticking becoming what we call Deuterium. 

One of the Protons would decay into a Neutron and we’d end up with a Proton and a Neutron crammed together and side-by-side with that there’d be a Positron flung off and a Gamma Ray flung off.  

The nice thing about Deuterium is when it collides with another Hydrogen you start to get Helium.  So you’re starting to build heavier Elements through this process.

Fraser:  This is exactly the same process that happens inside Stars.  For a few brief moments, the entire Universe was just like one great big Star.  

Pamela: In that one great big Star, we’re able to build up from Hydrogen to Helium and we even got bits of Lithium and Beryllium. One of the really cool things about Big Bang Nucleosynthesis is because when it suddenly shut off we were left with residual Elements that don’t normally end up by themselves in Stars because the process keeps going to completion.  

Normally you end up with Hydrogen going to Deuterium, going to different species of Helium and eventually building itself up into Beryllium and then to Lithium.  That Lithium generally quickly collides with the Hydrogen and goes into two different Helium-4 Atoms.  

Because of the way the process was shut off in the Big Bang, we end up with Helium-7 left that didn’t have a chance to end up combining to form 2 Alpha Particles. Alpha Particles is a fancy way of saying Helium-4.

Fraser:  How long did this process last?

Pamela:  Just 200 seconds, that’s the really cool thing.  All the Lithium-7 in the Universe pretty much was created in 200 seconds.  

Fraser:  Right.  And even the ratio – what was the final ration?  I think it was like 25 percent of the Universe is now Helium?

Pamela: Pretty much all the rest is Hydrogen.  There are just trace amounts of Lithium and Beryllium left behind.

Fraser:  Right, but that all got changed in just 200 seconds.  

Pamela: If it wasn’t for those 200 seconds who knows what would have happened.

Fraser:  Okay so then we’ve got a Universe of expanding Hydrogen and Helium and other Trace Elements.  Gravity takes over, starts to pull that material together and starts to form the first Stars.  They were just like balls of Hydrogen, right?

Pamela: Right and because they were basically balls of Hydrogen with admittedly 20 something percent Helium, they underwent different characteristics than our current Stars.  They were able to become huge.  We think that some of these Stars were able to get as big as 250 Solar Masses.  One Star 250 times the size of the Sun.  In these Stars they had what we call Proton-Proton reactions.  

This is pretty much the exact same set of reactions that were going on during the Big Bang Nucleosynthesis.  Eventually, they start to be able to build heavier things.  Eventually they are able to start building Carbon, building Nitrogen.  There are Super Novas – we ended up with heavier Elements over time. But that first generation of Stars, because there was no Carbon around to start the Carbon-Nitrogen-Oxygen cycle which is the next cycle that you get to when you’re done making Hydrogen and Helium, were able to build these giant Stars.  

They burned quickly and they died quickly and seeded the Universe quickly with heavier Elements.  Once we had those heavier Elements the size Stars that we were able to build changed.  Different types of Nuclear reactions were able to kick in at high temperatures.  

There is this process called the Carbon-Nitrogen-Oxygen Cycle that once you seed it with Carbon Atoms it’s going to halfway chew away and it does this at the type of temperatures you get with bigger Stars.  

A lot of times you’ll learn in Astronomy 101 class that all the Stars on the main sequence – Stars that are on a strip through a diagram of brightness and temperature that our Sun sits happily in the middle of, Stars that sit on the main sequence are all burning Hydrogen in their cores.  

That’s actually not true.  If you get yourself a big enough Star, it will actually start undergoing Carbon-Nitrogen-Oxygen burning in its core as well.

Fraser:  So, what’s going on?  I think we understand with the Hydrogen burning you’ve got essentially a ball of free Protons there.  Every now and then a Proton is being squished together with an Electron to create a Neutron. And then the Neutrons and the Protons are being pushed together and eventually you end up with Helium Atoms.  I think it takes 4 Protons?

Pamela: You start with the Proton-Proton chain.  This is what we have happily going on in our Sun.  In this case you take two Hydrogen Atoms, squish them together and you get what is called the Deuterium.  This is where you have one of the Protons decides it wants to be a Neutron and you give off a Positron and a Neutrino.  

Then the next stage of this is to take that Deuterium and you smash it into another Proton and you get Helium-3 – a Helium Atom that has 2 Protons and a Neutron and you give off some Gamma Ray light.  

Then you take 2 of those Helium (you have to let that process go a little bit until you get the 2 Helium), and you smash them together and you get a Helium-4 and 2 Protons go flying off.  Well the problem is, once you have this Helium-4, it really doesn’t want to combine with anything.  

This was mathematically a serious problem trying to figure out how is it that the Sun keeps going.  How is it that other Stars keep going?  How do you burn this Helium-4? 

 Luckily, the there is something that we call a Resonance that we’re not going to go into a lot of detail on where basically just the right energies and densities to cause Helium-4 to start turning into Beryllium and that Beryllium to start matching up with another Helium-4 to get a Carbon.  

There is an energy resonance that allows this reaction to happen at about ten to the 8 Kelvin and it’s perfect. It works and we call it the Triple Alpha Process and once you get that Carbon, then you can start, well Carbon mashed into a Proton that gets you Nitrogen.  

Nitrogen will then decay back into Carbon but a different type of Carbon.  So we’re building things, feeding it through the cycle and we’re starting to get Carbon-Nitrogen-Oxygen building up in the cores of Stars.  

Fraser:  Okay so that’s the whole point.  You’ve got your Hydrogen going to Helium and then the output of that is then turning into the Carbon-Nitrogen-Oxygen cycle and so you’re boiling down Hydrogen – fluffy Hydrogen into a much more compact oxygen, right?

Pamela: And the Stars actually go through fundamental changes as they go from one type of cycle to another.  You take a Star like the Sun and initially it will just burn through all the Hydrogen-producing Helium.  Helium is not hot and dense enough in the core of a Star when it is in the Hydrogen burning phase to get to that C-N-F cycle.  

Then you go through flashes and you end up with burning the Helium.  It’s a series of events where the Star collapses, changes core temperature, expands back out and you have the Star evolving in radius, evolving in core temperature, evolving in what type of burning is going on. 

As it burns hotter in the core it burns heavier Elements in the core.  It ends up actually creating shells of burning around that hot core as well so you end up with onionskin layers of Nuclear Synthesis. 

 In one part of the Star you’re perhaps creating Silicon while in another you’re still burning Hydrogen into Helium.  You’re just doing it at a higher level of the Star. 

Fraser:  What would be happening inside our Star?

Pamela: A Star like our Sun – we’re boring.  We’re eventually going to produce Carbon but we’re never going to get to burn the Carbon into something more exciting.  

You end up needing to have a Star that is about 1.4 times bigger than our Sun.  We’re not there.  But as you grow the Star you’re able to grow the size Element you’re able to build.   

Fraser:  That’s interesting.  So if we had a Star that was 1.4 times bigger than the Sun then it would take the Carbon and turn that into something heavy, Nitrogen, right?

Pamela: Well, we’d start ending up getting resultants of Oxygen and Sodium and Magnesium.  So the Carbon burning will start to get us to even more interesting Heavy Elements.

Fraser:  How far does this process go?

Pamela: As you get up eventually to a five Solar Masses Star, that’s when you start to be able to burn Neon.  Out of that you get more Oxygen and more Magnesium. 

With bigger Stars yet at ten Solar Masses you start to get Oxygen burning. At twenty Solar Masses you start to get Silicon burning.  Eventually though you get to the point that through the Silicon-burning process you’re creating Iron through the nuclear burning.

Fraser:  So your output is, like the end of a factory line, Iron is coming out.

Pamela: The problem that we run into is that with Atoms that are lighter weight than Iron.  When you fuse them together they release Energy.  They are happy to give off Energy through this process.  

For instance during the Hydrogen-Hydrogen, you end up giving off 1.44 mega-Electron volts of Energy.  So as we produce Helium-4 we’re giving off more than 20 mega-Electron volts through that entire process.  We’re releasing Energy through all these different burning processes.  

Once you get to Iron in the core, you can’t combine two Iron Atoms.  In fact you can’t combine Iron and anything and have it release Energy.  You have to add Energy into it to get that sort of process to take place.

Fraser:  Right and I remember the whole Star is being held up against all that Gravity by the Energy that is coming out of this fusion reaction – the light pressure.  So you’ve now instead of having excess Energy keeping the Star out, you’ve run out of Energy.  

Pamela: In this case there’s nothing supporting the outer atmosphere of the Star anymore.  So the entire system collapses.  As it collapses you end up with things colliding violently.  You have that Energy getting injected and you’re able to get all sorts of massive reactions going on.  This is in fact a Super Nova.  

We have Gamma Rays flying out radically.  We have Neutrons flying out radically.  It’s this wash of Neutrons flying through the collapsing atmosphere of the Star that causes what we call the Rapid Process (R-Process).  

Take a happy little Atom and bombard it with Neutrons and it is going to grow.  If you bombard it with Neutrons fast enough, those Neutrons can’t decay into Protons at a reasonable rate to keep it at a lower Atomic Number.  

In fact you’re able to build these crazy large Neutron-rich things that will eventually decay into nice stable Atoms.  It’s out of this R-Process that you get Gold, Silver and a lot of the Heavy Metals that we deal with day-to-day.

Fraser:  How long does that process take?  I know that we’re talking way back when with the Sun that it takes hundreds of thousands of years for the light to get from the core of the Sun to the outside the Sun.  

It sounds like this whole process, once you get like a train wreck on the one [Laughter] end of the process, it must take time for it to ripple through the system, right?

Pamela: Super Nova can have core collapse that takes place in the time scale of milliseconds. It’s going to take time after that for all the radioactive particles that have been created to decay away. 

This is part of what causes the slow decay of the light curve. It is part of the time scale of how long different Super Novas stay at different brightnesses depends on the ratios of the different Elements that occur and how they’re slowly decaying away.  

But Super Nova themselves, it’s milliseconds with this radical environment of Neutrinos and Neutrons and Gamma Rays all passing out through these collapsing layers of the Atmosphere and creating a shock-wave and pushing things outward.  It’s an amazing process that people are struggling to try and do good three-dimensional models of to understand everything that’s going on.  

Fraser:  But it’s just amazing to think about that, right?  I mean you’ve got a Star – I guess with a Super Nova Star they don’t last very long. Let’s say you’ve got a Star that has lasted for millions of years happily burning, upgrading the stuff that it’s burning you know going up through the Table of Elements and then it hits this wall of Iron. 

It’s just like a brick wall.  Like a car hitting a brick wall.  [Laughter] Milliseconds later, the Star is gone from its previous form.  Black Hole forms – you get the explosion and all these new Elements.  It blows the mind.

Pamela: There is one other way to get some of the Heavy Elements.  This is the way like nobody talks about.  I love some of the things that we just propagate basically a Mythology of false information.  

There’s this thing called the S-Process where there are Neutrons getting produced in the cores of Stars all the time.  In old Massive Stars, you’re producing enough Neutrons in the center of the Star that as Neutrons pass out through the Atmosphere, they’re able to bombard Atoms hanging out in the Atmosphere and get captured.  

Then they undergo what’s called Inverse Beta Decay where that Neutron converts itself into a Proton and Positron and a Neutrino.  In the process you’re able to build heavier and heavier Elements in the Atmosphere of the Star.  So there is one other way to get at some of the Elements.  This is for instance one of the ways we get at Strontium.

Fraser:  Are you sure that’s it?  I mean that’s it for Stars but what about Black Holes?

Pamela: Well, not just Black Holes but also White Dwarfs and Neutron Stars – anywhere you have an Accretion Disk you can end up building up again another situation with the densities and the temperatures are sufficiently high that you can end up with Nuclear Reactions.  

When you see a Nova, not a Super Nova but a Nova, one of these situations where you have an exploding Accretion Disk, that’s runaway Nuclear Reactions. So there are all sorts of random little extra places that we can start to get heavier Elements emerging.

Fraser:  Right, so you’ve got material piling up around a Super Massive Black Hole and for just a moment there, the region has the right density and the right temperatures to act like a Star.

Pamela: And with Super Massive Black Holes their Accretion Disks can actually maintain some of this material for fairly long periods of time.  It’s the White Dwarfs that you end up with these short outbursts, these recurring Nova events where essentially the White Dwarf is sitting there, gravitationally sucking Matter off of a nearby companion.  This only happens with binary systems.  

As it sucks the Matter off, the Matter builds up and builds up until you end up with Explosive Accretion Disks.  Once you’ve cleared it out, the process starts over again and then you suck Matter off, build the disks and build the disks… and it goes off again.  

So this is again something that has found a model and here it’s complicated because for reasons that we’re still trying to figure out the rate at which White Dwarfs suck Matter off their companion isn’t always constant.  

The rate at which the Accretion Disks explode isn’t entirely constant.  So there’s lots of neat Physics still waiting to be explored.  

Fraser:  Okay, so let’s run through a couple of examples before we wrap this up.  Just so people can get a sense of the story.  Let’s imagine you have a glass of water – where did the water come from, Hydrogen or Oxygen?

Pamela: The Hydrogen probably came from the Big Bang.  There’ really nowhere else that you get Protons.  Then the Oxygen probably came from a Star bigger than our Sun.  You can get Oxygen from a Star the size of our Sun but you’re going to get more of it as you start to get bigger Stars.  

You have to wait for these Stars to die.  During the last years of the biggest Stars, there’s mixing and they breathe out their Atmosphere’s Planetary Nebula.  It’s this breathing out; this exhaling of materials that have been mixed that allows you to get at the Oxygen from the heavier Stars.

Fraser:  So to make a glass of water you had to go to the Big Bang store to get [Laughter] some Protons.  Then also you had to go to an old Massive Star that was sloughing off its outer Atmosphere firing out Oxygen.  Then mix those together and you got water.

Pamela: And you could also have gotten the Oxygen from Super Nova.  We can’t know exactly where any of them came from.

Fraser:  Right, right.  Okay what about a tree?

Pamela: [Laughter] a tree is mostly Carbon.  So Carbon, again we’re getting this through the exhaling of elderly Stars where they’re breathing out their outer Atmosphere, which has been enriched, with Carbon through different mixing processes.  We’re also getting that from Super Novas.

Fraser:  And my wedding ring?

Pamela: That’s all Super Nova.

Fraser:  Right – only a Super Nova.  It had to come from a Super Nova.  

Pamela: And that’s kinda cool.  

Fraser:  It’s really cool.  I don’t think my wife would agree but…. [Laughter]  That’s the coolest thing ever.  Well, I think that covers the show for this week.  And now I hope that you’ll look around at all the stuff and even the stuff that you’re made of and you can think back to the famous Carl Sagan quote –we’re all made of Star stuff.

Fraser Cain:  Yeah and you’re off to Dragon Con.  I know we’ve been saying this over and over again, but this is it.

Dr. Pamela Gay:  I’m going to be at Dragon Con and there will be an International Year of Astronomy booth over in the Marriott Hotel and Pod casting science space and a whole lot more over in the Hilton.  

I even got myself onto one of the Star Wars panels where we’re going to be talking about, “Could the Star Wars Galaxy really happen?”  It’s going to be a fun packed week and I’ll have all the details up on my blog probably Wednesday or Thursday.

Fraser:  Alright and Phil’s going to be there and all the folks from Skepticality.  It’s going to be a lot of cool people there.  I get to take a week off because you’ll be recording the show, so it will be great.  

Actually it probably won’t be a week off because we’ll probably do our show next week and then we’ll probably post the Dragon Con show the week after that.

Pamela: We’ll see what happens.

Fraser:  Yeah we’ll figure it out.  There will be something every week forever.  All right well let’s move on.  Our series on the basic forces of the universe continues.  Last week we covered gravity and this week we’ll handle electromagnetism. 

You probably know electricity and magnetism are just two facets of the same force and they play a huge role in some of the most energetic places in the Universe.  You can’t talk Astronomy without understanding these.  

All right Pamela so we’re ready for Part 2.  I’m going to guess we learned about magnetism first so maybe you should give us just a little bit of background.

Pamela: Well, the fact that these are forces is one of those things that confused us for no end.  There was first this whole that there are rocks out there that can pick up other rocks and they cause attraction and repulsion and this was just highly confusing.  

But, it allowed us to do things like build compasses. Compasses were probably one of the most useful things right after fire in terms of helping human beings expand out across the planet. Compasses allow us to find our way across water. With society growing up around the Mediterranean, being able to navigate by sea was kind of important.

Fraser:  I guess that must have been a pretty amazing discovery to think that you’d float a little piece of metal or rock on water and it will always point in the same direction.

Pamela: You’ve got to wonder what sort of magic and gods and all sorts of other mythology was involved with that.  It’s something that we didn’t really understand until the 1800s, but we’ve known about for basically forever.  That’s just one of the strange, why do things fall?  Well they do.  Well why do magnet’s needles point north, well they do.  

It took a long time to sort it out. Trying to bring magnetism and electricity together was one of those things that actually first started to happen out at sea. Sailors were being subjected to St. Elmo’s fire, to lightning, to all of these electrical effects and noticing in the midst of all of this chaos that their compass needles are going haywire too.  

Here you know how these poor superstitious sailors, who don’t have the education to know any better, watching their magical compass needles spin crazily, watching their masts start to glow with built up electric charge and then quite often all of this leads in their ship getting struck with lightning.

They had to have evoked all sort of craziness and now we have the science to explain the craziness. The moral is you don’t want to be the tallest thing on the ocean during a storm.

Fraser:  So from electricity, how did they start to understand that?

Pamela: There are all sorts of neat things but it often all boils down to cat fur and amber, or wool and amber.  There are different things you can do to build up static electricity.  This can lead you to doing all sorts of neat experiments.  

For instance, if you rub cat fur on amber or plastic you can start to build up charge. You can transfer this charge if you have a metal cylinder.  One really neat experiment we do in a lot of freshman physics courses is we take a metal cylinder with a piece of glass on both ends of it. 

Going into the metal cylinder we usually have a little finger of metal with a piece of foil attached to it.  There’s usually an insulator of some sort to protect the piece of foil from the little metal finger going into the cylinder.  

If you rub plastic with wool and then touch the metal cylinder it will deposit charge and you can do this over and over and over again. Very slowly as the charge builds up you can start to deflect the small piece of foil in the center.  This is the type of experiment that they could have done a couple hundred years ago.  

Fraser:  Actually I have a great experiment for every one. If you want to pause the pod cast.  Find something long and plastic like a knitting needle or something like a straw. Rub it against cotton or wool ideally and then turn on your water off your tap really lightly so you have a thin little stream coming down. 

Once you’ve rubbed the plastic with the wool hold it right next to the stream of water and you will actually find the water bend sideways.  It freaks the kids out. [Laughter]

Pamela: The reason that works is because there’s charge in the water.  It’s not all neutral and you’re actually getting attraction. That’s a really cool demo I’m now going to have to try with my students.  I didn’t know about that particular demo.  

There are all sorts of neat little things you can do with electricity and magnetism.  For a couple hundred years all sorts of people including perhaps most famously here in the United States, Benjamin Franklin, looked for all sorts of different ways to experiment with electricity and find new and interesting ways to hurt themselves in some cases.

Fraser:  How do they get the sense that they were connected?

Pamela: This whole lightning strikes and compass needle goes crazy was indicative that there was something going on.  You can actually start to generate electric current through wires by using magnetic fields.  If you have a moving magnetic field near charge then you can get the charge to move too.  It’s one of those cool things.  

Take a loop of wire move a magnet through the wire and you’ll end up getting current moving through the wire.  This is in part how generators work.  You take and you either rotate the wire around the magnets or the magnets around the wires and you can start generating all sorts of different types of current depending on how you have the wires set up.  There’s this clear, physical, tangible experimental evidence that something is going on.

Fraser:  Right, so once again I think the experiment reads you take a coil of wire and then you move a magnet through the middle of the coil and assuming you have a light bulb on the end of it, the light bulb will glow every time you move the magnet in and out of the coil of wire.

Pamela: The other thing is once you start figuring out how to generate electricity, if you run electricity around and around a coil; that generates a magnetic field.  You have two different sides of a coin facet to this where magnet going through wire generates electricity, electricity going through coil of wire generates magnetic field.  

This is actually in part what’s happening in stars.  We don’t so much have a coil of wires, but instead there are plasmas (charged particles) moving in circular motions around the insides of stars and this motion of the charged particles generates magnetic fields. That’s what leads to sun spots eventually, that’s what leads to the Earth’s magnetic field.  

Everything seems to come down to what happens when you take an electron, what happens when you take a proton, what happens when you take a calcium atom that’s missing a few electrons.  What happens when you get this charge moving is you get magnetic fields.

Fraser:  Back to my question, how do they come together?

Pamela: It all came down to a rather brilliant man by the name of Maxwell who was working on trying to figure out how to mathematically pull all of these pieces together.  We had laws describing mathematically how magnetism worked. We had laws describing mathematically how electricity worked. 

Maxwell sat down and realized that all these sets of equations could be brought together into a single formalism that combined both the electricity and the magnetism through basically four different equations.

Fraser:  So we’ve got then four different equations that then allow you to calculate how the electricity and the magnetism in some situation are going to be interacting.

Pamela: It all comes down to, “How do charged particles move and how do magnetic fields change?”  If either of these two things is happening, if either a charged particle is moving or the strength of the magnetic field is changing, you’re going to generate electric fields. You’re going to generate magnetic fields and you’re going to get all sorts of neat secondary effects.  

One of the things we don’t think about as we’re wiring up our houses is if you had direct current, if you had current that was always flowing in one direction and somewhere in your house and you ended up with too much wire and you coiled it up you could end up with small pockets of magnetism in your house.  

As it is with alternating current, we can still end up with small pockets of magnetism but the direction of the magnetic field is constantly changing so that’s not as likely to do weird things to your house.  

If you leave a nail inside of a magnetic field that’s constant for too long you can actually transform that nail into a magnet because over time that magnetic field can actually change the alignment of the atoms in the nail.

Fraser:  Let’s bring it back to Astronomy then.  What role does electromagnetism play in some of the biggest forces in the universe?

Pamela: Magnetic fields are pretty much where it’s at.  One of the scariest parts of the field of astrophysics is something called magneto-hydro dynamics.  It’s the study of basically, if you have stuff that’s acting like a liquid and there’s charge in it, it generates magnetic fields, let’s describe this in three dimensions using fancy computer models.  It’s probably the most complicated thing to try and study.  

It’s necessary because things like the accretion discs around Black Holes generate magnetic fields. Stars generate magnetic fields.  The faster rotating the star, the stronger the magnetic field.  When we pull all of these pieces together, it leads to side effects.  

There are jets.  The jets of a Super Massive Black Hole are nothing more than the North and South Pole of a giant magnet and particles are getting streamed out that northern and southern pole.  Charges are getting carried along and flung out the ends.  These are violent, violent behaviors.  

Hyper nova and gamma ray bursts, are considered to be in part, driven again by jets potentially again driven by magnetic fields.  Where there’s violence, quite often there are magnetic fields.  Understanding these things allows us to understand some of the coolest most high-energy events hanging out scattered around the Universe.  

Then there are just low-level magnetic fields that could have different effects on galaxy formation.  We’re still working to try to figure this out.  We know that there are magnetic fields permeating through Galaxies. We’re still working to figure out how does that effect star formation. 

How does that effect the streaming of material that’s getting spit out as super novas shock the nebula that they sit within?  We’re still sorting all of these secondary things out and we have to understand the magnetic fields to understand what’s happening.

Fraser:  I know one of the more recent theories about Super Massive Black Holes is that those jets that are coming out of them are helping to see the Galaxy and help collapse star formation and seed some of the heavier elements.  Those big magnetic fields operating from the Super Massive Black Holes might have a big impact as well.

Pamela: It’s basically like a giant magnetic sprinkler head.  We have all of these nuclear reactions going on generating heavier and heavier particles and they are not neutral.  

They don’t have enough electrons to balance out all of their protons in a lot of these extremely hot dense environments. Any time a particle is charged it’s susceptible to magnetic fields.  

So it’s possible that these Super Massive Black Holes can basically scoop up the charged particles, shoot them out through the magnetic fields and let them rain back down on the Galaxy.

Fraser:  Can we get a sense of scale here?  We’ve got a bar magnet or the Earth’s magnetic field, how does that compare to say the magnetic field of the Sun or a Pulsar or something like that?

Pamela: Here on the surface of the Earth your standard bar magnet can totally overwhelm the effects of the Earth’s magnetic field or of this little tiny magnetic field.  It’s like order of a few tens of a few micro-teslas.  It’s not that big.  We can generate in the lab thousands of teslas if we feel like it.  

The Sun is measured in micro-teslas. It’s about a hundred more powerful in general.  Once you start getting out to some of the bigger things out there such as Pulsars, Neutron Stars that are rotating quickly, accretion discs and things like that you can start to get to thousands of times stronger, tens of thousands of times stronger. 

In fact the magnetic field of magnatars, are measured not in micro-teslas but measured in giga-teslas.  The micros are like fractions and fractions and fractions of teslas where as the giga is billions of teslas.

Fraser:  So we’re talking trillions of times more powerful than the Earth.

Pamela: Yeah.  You might say that we really don’t want to be anywhere close to a magnatar.  When the magnetic fields and magnatars rearrange themselves there is so much energy involved that, one that did this on the other side of the center of the Milky Way a few years ago was actually able to damage satellites orbiting the Earth because it let off so many high energy particles, so many high energy gamma rays.  There’s a lot of energy tied up in all of these magnetic fields.

Fraser:  Okay I’m going to channel my six year old daughter here for a second and ask the kinds of questions that she would I’m sure would want to know.  I just have to say why?  Why is there magnetism and electricity?  What is the underlying reality at work here?

Pamela: At first glance it’s the way the universe was built.  When you start looking at the way particle physics describes it all of these forces are immediated by different particles. 

So last week with the force of gravity we had the graviton running back and forth being – you, you be attracted to this and pulling things together.  With the electromagnetic force we both have things flying apart and coming together.  That’s one of the really cool things about the electromagnetic force. 

Just like with gravity, the electromagnetic force can work over huge distances. Just like the electromagnetic force it gets weaker with distance.  It turns out that just like the force of gravity, the electromagnetic force has a mass-less particle running around going – you go over here, you come over here and in this case that particle happens to be the photon, the particle of light.  

When you have two magnets repelling each other across the table you don’t see a beam of light going back and forth between the two of them.  This is where we start talking about exchange particles and virtual particles.  

Mathematically we describe everything with the exchange of photons but that’s not actually something we’re generally going to see. We can actually see how light effects matter.  The electromagnetic force is the one that holds together pretty much everything around us.  

The reason I’m not falling through the chair I’m sitting on is because the electromagnetic force is bonding all the atoms together with covalent and ionic bonds, which is just a fancy way of saying different atoms are sharing electrons.  

The reason that I am able to stretch some things and fold others is because of the fluidity of how the atoms are bonded together. All of these things are determined through the electromagnetic force and I can start to change things.  

I can start to remove electrons; I can start to basically change how atoms are structured to the point of even causing fusion if I just hit them with enough light.  

This was part of the photoelectric effect that Einstein got his first Nobel Prize for.  If I shine a nice happy red light on a piece a metal there is a pretty good chance that I can beam that piece of metal all day long and not necessarily get any electrons flying off.  

If I change the color of that light and change it more to the blue and more to the blue and more to the blue making the light higher and higher energy, eventually I’m going to start knocking electrons off of those atoms.  

What was realized is that light, while appearing to be this stream of flowing color is actually not waves but individual particles. Each packs an individual little punch where red light carries less of the punch than blue light.  

Atoms have electrons that are held in place and with a certain amount of energy can get knocked to a new place.  Just like having ten million little puppies butting their little heads against my leg is probably only going to make me slightly bruised and ten million pit bulls will cause me to fall violently to my knees, the blue light is perfectly capable of moving electrons. 

Whereas the red light just causes the electrons to go, “Yeah, so go on, do your best.”  It’s that energy that can cause electrons to get removed from atoms.

Fraser:  So how do the photons relate to the magnetism and the electricity?

Pamela: They work to carry the force.  Here is where it starts to sound more like magic than science unless you start getting into the nitty gritty quantum mechanics of all of it.  

The photons basically working as virtual particles getting evoked in lots of fine diagrams are going back and forth communicating from one electron to another; you too should be repelling one another.  Communicating from one electron to one proton, you two should be attracting one another.

In this way they are the carriers of the force.  They are the ones that communicate what’s going on and through their motion at the speed of light they are also able to communicate in some ways the distance between things.  

Magnetic fields don’t move instantly.  If I move a magnet it’s going to take the magnet that’s interacting with it time, the amount of time it takes a photon to move from one magnet to the next to realize that there has been a change in the force it’s experiencing.

Fraser:  So magnetism works at the speed of light just like we know electricity goes at the speed of light.

Pamela: Yes, so we have gravity, we have electricity and we have magnetism, all traveling at the speed of light because they are communicated by particles with no mass.

Fraser:  So when you said that everything that we see in the Universe, all the light that we see, all of the forces that are holding together the atoms that we see, the molecules, that’s all electromagnetism.

Pamela: That’s all electromagnetism with gravity sometimes mixing it up a little bit.  We have gravity out there changing the color of light, changing the path of the light. But the structures we see are all electromagnetism.  The structures we’re sitting on, our computers, all of that is electromagnetism.  

Everything that allows the computer, the I-Pod the I-River, the whatever it is you are listening to us on to function.  All of that is described through electromagnetism.  Through various sets of rules that define how circuits work, and how one charged electron interacts with different properties in atoms.  

This is perhaps one of the most complicated forces.  Gravity is quite happy to say, you have mass, okay I’m going to pull on you.  With electromagnetism you start to get into the individual characteristics of different atoms.  

You look at what are the geometries of the electrons? What is the susceptibility of a particular substance to having its electrons moved around?  

Electrons move readily in metals.  Metals become magnets. Metals conduct electricity. All of these things are united together. At the same, pick take up a hunk of wood and it could care less if you have a magnetic field or a flow of electricity.  It’s just going to sit there and be wood and refuse to conduct and refuse to repel and refuse to attract.  

It’s all the electromagnetic force and the structure of atoms define how that electromagnetic force is able to do all the amazing things that it does.

Fraser:  All right so let me see if I understand this correctly.  I could take for example a magnet pulling on some other magnet onto some piece of metal and I could turn that into electricity, right, either by moving the magnets through the wire or whatever.  

I could turn that electricity into light or also magnetism here or I could use that electricity or magnetism to knock electrons off of some atoms to make them either stick together or break apart and this is all just the same force acting?

Pamela: This is all the same force even down to light bulbs where when you try and get electricity to flow through things that are more resistive to its flow like carbon filaments.  

The friction is the wrong word, but it’s the one people try to use, don’t say friction.  The resistance of that carbon fiber to having the electricity flow through it is going to cause the atoms to move, to heat up, and to generate light. 

That’s again electromagnetism where as the electricity flows through something that conducts easily, a normal every day wire, to moving through something that is resistive like a filament we generate light.  

All of these things are electromagnetism and it all boils down to the structure of the material the electricity is attempting to flow through or the magnetic field it is attempting to interact with.

Fraser:  Now we’re treating it as a separate force from gravity. Is there any inter-relation between electromagnetism and gravity, or are we not ready for that yet?

Pamela: No, we wish we understood how these two things could come together, we don’t.  At the earliest moments in the first fractions of a fraction of a fraction of a second of the Universe, all the forces were one.

Then gravity went off and went its own way.  The other three forces hung out together for a while and electromagnetism is not related to gravity.  Gravity can affect how light changes, but magnetism and electric forces are their own happy little things.

Fraser:  So I guess we’re going to have to wait until the last part of this series where we win our Nobel Prize [Laughter] to unite the forces.

Pamela: Exactly.

Fraser:  All right, well we’ll look forward to that then.  Be patient everyone, that’s coming.

Pamela: We condensed the entire topic of four college courses into 30 minutes. So if we were vague and we didn’t dig into details it’s because I don’t have a blackboard.  There are some excellent books out there.  

There’s E & M by Griffith if you ever really want to learn more about E & M than your calculus-knowing mind thought it wanted to know. If you really hate yourself, Jackson’s E & M is a book that has put the fear of E & M into pretty much all grad students who have studied physics at one point or another.

Fraser:  I don’t think that people really understood how it’s all inter-connected. Pretty much all of the things you are interacting with are all generated from this one force in different facets. In fact we talked about this before, that you can take light and freeze it into matter.

Pamela: Exactly.  We talk about quantum mechanics as if it was dealing with its own separate little set of forces.  It’s not.  Quantum mechanics deals in part with how the electromagnetic forces dictate how electrons move. 

It deals with how light is generated, how things come together, and how electrons are able to go through different potential wells, how fusion and fission, how all of these different things are able to take place.  

This is all electromagnetism and it took quantum mechanics to explain how all of these different things come together.

Frazer:  We’ve got two more forces to go so I think that will be maybe one maybe two more weeks.  I don’t know how much we have to talk about.  

Thanks Pamela and maybe there will be a Dragon Con episode next week, it’s all going to be a mystery so stay tuned, we’ll figure it out.