Video Transcript: White Dwarfs

And the first one we're going to look at is white dwarfs.   We saw an example of a Ring Nebula, I think it was, of a nebula with a white dwarf in a center, and I'm going to show you just a couple other examples.  

So the first picture in our gallery is often called the Cat's Eye Nebula.  This is another example of a planetary nebula.  It illustrates how different these all can look.  But these are the outer layers of a star that have blown off into space and you can see the star that's leftover in the center, and that's the white dwarf.  

Let's look at another example.  The second picture is what's called the Spirograph Nebula.  If you've ever played with a Spirograph, it's one of these toys where you draw and these little gears move it around, and you make all these spiral patterns.  You can kind of see that reflected here in this planetary nebula.  But again, you can see the star in the middle, which is a white dwarf.

Remember white dwarfs?  We saw them on the H-R diagram?  They're cooler; they're bluer…  No, wait.  No, wait.  They're hot, right? They were way on this side of the H-R diagram.  They're really hot.  But they're fainter; they’re fainter because they're so small.  

So what are we talking about here?  What do you mean by a small star?  Well, this is the core of that star, right? We had the star burning and all these shells throughout its life.  But the ashes that were left over, now, it might be that those were Helium ashes; depending on the size of the star, those might be Carbon ashes; maybe it's Iron ashes that were leftover.  But the point is, there's this ash, this material that cannot be burned, that's leftover in the center of the star.  And while the outer layers are flying off, that inner material is still very heavy and gravity is very strong, pulling down on it.  

And when nuclear fusion, it's not happening inside that star.  Now think about this with me for a second.  A star normally begins as this big cloud of gas.  And gravity's pulling down, down down, and eventually it gets to a point where fusion begins.  And fusion is like heating it up.    And so there's some heat and some pressure pushing back against gravity.  I mean, imagine taking a… what's a good analogy… you know, you got something you're squeezing it like a ball, that's partially deflated.  Like a ball that doesn't have enough air in it, and you squeeze it down, eventually it starts pushing back because there's pressure inside there. You just had to squeeze a little ways and it started pushing back.  

That's what fusion is doing.  It’s creating gas pressure through this heat, and it pushes back against gravity.  And for the long duration of the star's life, those two things are in balance.  That's the main sequence.  Gravity is pulling down, gas pressures pushing out, they’re in balance.  But that's driven by fusion and when fusion stops because you can't burn anymore, you don't have enough mass to burn, well, then there's nothing to hold up against gravity, so gravity continues then to collapse.  So this gas weird material that's hot and dense, it collapses, and it's warm, it's hot, but not hot enough to hold up against gravity.  And so a white dwarf is where this continues to collapse and get smaller and smaller until something holds it up.  What is that? We'll talk about that in just a minute.  So how small are these things?  Well, let's take a look.  

This bright, bright star in the center here, a picture, this is the third picture in the gallery, it’s Sirius. The Star Sirius, sometimes called the Dog Star because it's Orian’s hunting dog.  It's the bright star, it's one of the brightest, it is the brightest star in the sky.  But what you'll see next to it, in the bottom left corner, is a faint little companion, and this actually this is a binary system.  These two stars orbit each other.  And that tiny little star, you'll see that it is much, much fainter, is a white dwarf.  And it's fainter, not because it's cooler, you'll see it's just as blue as Sirius is, it’s the same temperature really, it's still really hot, but it's so much fainter because it's so much smaller.  So how small?  

Okay, well, the gravity is collapsing this star, the core of this star, down, down to out until the atoms inside there are literally pushing right up against each other.  In particular, the electrons on the outside of these atoms are bumped up right up against each other and there's some laws of physics that say electrons cannot get any closer after a certain point; like those electrons have to stay apart.  

Now normally, you think about two charged electrons, they're repelling each other, they're going to stay a long ways apart.  But gravity is so strong that it's pushing them until they're effectively touching.  We call this electron degeneracy.  It's, in principle, as close as atoms can get.  It is the limit to how close atoms can get in the universe, before they disintegrate and are no longer atoms.  

Okay, so that's how small these things are getting essentially, you know what I'm saying?  That's dense!  It’s like, dense!  Okay.  So how small is that? Well, it's like taking a star, the size of the Sun, the mass of the Sun, and shrinking it all the way down to being the size of the Earth.  

That's a huge, huge reduction in size.  So these white dwarfs are like the size of an earth out there.  Remember that first was first pictures, I showed you, the pale blue dot, that tiny little dot of light that was the Earth?  That's how tiny we are.  Those white dwarfs are stars that are that incredibly small.  

Now, that's not where the story ends for compact objects.  So these are weird objects.  I mean, they're so dense that if you had a teaspoon of white dwarf stuff, and you put it on Earth, it would weigh as much as an entire elephant.  That's how dense this material is.  Or if you had a sugar cube, it would be like a ton, it would literally weigh one ton.  That's how dense a white dwarf is.  

But in some cases, if you have a very massive star that you begin with, then the mass is even bigger than what would become a white dwarf and gravity is even stronger and so the force of these atoms literally bumping up against each other is not enough and in that case, what happens is, the atoms literally annihilate each other.  The electrons and the protons annihilate, and all you're left with is neutrons.  And a case of that, the entire star, it's no longer made up of any particular element, it is entirely neutrons, which is weird.  And in that case, the star continues to collapse all the way until it's like the size of just a city.  Like imagine Chicago, in the United States is a star that size.  And what happens in that case is the star which was once maybe orbiting once a month, like our Sun, has collapsed down, down, down, to the size of the city.  And just like a figure skater, or someone when you spin and you bring your arms in close, you spin really, really fast, well, this star starts spinning so fast, that these neutron stars, they're literally spinning faster than a blender. You get these stars that are the size of a city, but spinning 500 times every second, just spinning around, and their magnetic fields are so strong that they're beaming radio waves in all directions.  That's how they were discovered.  

In the 1960s, these bizarre objects called neutron stars were discovered because they found these incredibly precise, bright flashes of radio light coming from outer space.  And they didn't know what these could possibly be.  What could cause, what astronomical thing changes thousands of times a second.  There's nothing like that.  And so they were initially given the name LGM for Little Green Men because they thought, well, maybe these are aliens that are sending us a signal.  But they found more and more of these things and they eventually put the pieces together.  These were neutron stars, these bizarre objects.  

Okay, crazy.  In the next video, we're going to see it gets even crazier, we talk about black holes, because that's neutron stars that have now collapsed even further to the most bizarre objects in the whole universe, black holes, but before we have to appreciate one more cool thing about white dwarfs, and that is that in the case of some of these stars, this core of a white dwarf is like Carbon and as that Carbon material sits in that core, it cools.  

Now at this point, it's no longer fusing, it's no longer producing heat, it's just hot ashes of a star.  And just like in a campfire, those hot ashes are going to glow and as they glow, they're going to get cooler and cooler and cooler and nothing can speed that up, really, it just has to take a long time to cool down; that’s just what happens.  

But as it cools, you might think, well Carbon, it might form kind of like a crystal structure because Carbon does that.  In fact, when carbon forms one particular kind of crystal structure, that's what we call diamonds.  So some astronomers have predicted that perhaps these stars after they've cooled down, actually solidify as enormous diamonds, like the size of the entire Earth.  So it could be out there in space there are floating around Earth sized diamonds, these old, these old white dwarfs.  

But the other piece of this story with white dwarfs that's relevant for us is related to the appearance of the age of the universe.  We've seen several instances already in our course of observations that suggest that our universe may be older than what people would be led to believe from a traditional reading of the first chapters of Genesis.  I mean, you first read that, and these are days that God created the Earth, and here it is.  And then history unfolds over the next 6000 years.  

But our observations of the world that God created seems to paint this picture that maybe things look older than they are, or maybe the universe is older and we don't really know, but what we do know is the universe looks old. The universe looks old.  

And this is another piece of evidence pointing to say the universe looks old.  Why?  Why is that the case?  Because white dwarfs take a very long time to cool down.  They're very hot, and they are radiating out into space, and those things can be measured.  The temperature can be measured, and how much light it’s giving off can be measured.  And just like if you had a cup of coffee sitting on your table, and the heat is leaving that cup of coffee, it follows a very predictable curve.  A cooling curve.  

And those laws of physics are the same everywhere, anywhere, it doesn't matter what object it is, as it cools down, it follows the same laws.  And so those same laws apply to white dwarfs as they're cooling down.  And we can see white dwarfs at various stages of that cooling.  

We know how hot they started at.  We know how hot some of them are right now.  And so what we can see is we see some white dwarfs that clearly must have been cooling for billions of years.  Otherwise, they couldn't be at the temperature they're at.  And we see some white dwarfs that have just started cooling off.  So, we're seeing them at multiple stages.  But this was one of the first indicators that our universe might be old.  I mean, it looks really old, because these things are sitting there cooling off, and boy, how could they be this temperature unless they've had a lot of time to be cooling off.  

Now, I mentioned this, this particular observation in particular, because as we get into the last Unit of our course, and we look at other evidence of kind of history of the universe, how big it is, and some of the observations that suggest the universe looks really old, what is amazing, really about all of this, and maybe it's not surprising from a Christian perspective, but what is amazing is that there are many very diverse observations that all paint the same picture.  That is to say, cooling of white dwarfs is totally separate from our understanding of, you know, cosmology, and both of those things paint the same picture of approximately the same age of the universe.  

All right?  So the point is these observations are consistent, and that's what's not surprising as Christians is that of course, they're consistent because we believe that there is a consistent person who made this creation, and so everything has to fit that consistency, that order that God has built into creation.  

Okay, good stuff.  I'm excited for the next lesson.  Black holes.  Here we come.  All right, we'll see you next time.