Video Transcript: Birth and Death of the Stars

Maybe like a really old tree, there are some trees that have lived for thousands of years and it's a similar problem, you know.  How can you know how old it really is?  How can you know what it was like, what its story is?  We clearly face this problem in the universe in general, but in stars in particular.  How can we know anything about how stars begin because the stars we see are already here?  Well, the story has been unfolding.  And there's a variety of ways that we can see stars in the process of forming and in the process of dying, or, you know, blowing apart, whatever you want to say.  And so that's what I'd like to show you in this particular video is sort of a picture of the birth of stars and the death of stars.

Now, as I alluded to before in an earlier video, there's a beautiful living parable here, a way in which God has written into the fabric of the cosmos an analogy, I believe, for our own lives.  I mean, isn't there in the Scriptures where it says we'll all shine like stars in the universe and it's a beautiful picture to think of how a star is born, a star lives its life, a star dies.  But that's not the end of the story for a star.  That's where our story will end in this video, but in later videos, we'll see that actually, there's something that comes afterwards for stars.  And that's an interesting parallel for us in our lives where our mortal bodies are just the beginning of the story. 

So let's start here with a picture of what's often called a stellar nursery.  In fact, this picture is one of the earliest most famous pictures from the Hubble Space Telescope, it's sometimes called the Pillars of Creation because this is where new stars are forming.  And this picture is of an enormously large, huge cloud of hydrogen gas.  And the colors here are not really what the colors would look like if you looked at this through a telescope.  This entire Nebula is red, because hydrogen gas glows predominantly in the color red.  But the colors you do see are indicative though, of differences.  And there's different types of gas in this cloud.  And the colors are meant to illustrate that.  The point though is that this is a large, cool cloud of hydrogen gas.  It's relatively cool. 

Okay, now, it's in this huge cloud that you can kind of see it, especially look at this in the gallery, on the little tips of these little fingers that are sticking out, just not the big fingers, but tiny little fingers, like there's a little tiny one up there, right there, on the very end, little clumps of this hydrogen gas are collapsing down, collapsing down under the force of gravity. And as it collapses down, down, down, down, down, eventually, the force is so great on this cloud, that inside, the process of nuclear fusion ignites and starts creating heat.  And that heat eventually escapes as light from these protostars.  And as that happens, it's blowing off heat material, the material starts to fly outward as well, starts to clear out the other gases in the area and a new star starts to have its solar system. 

Now, how do we know this?  We can't watch this happen. As far as we know, this takes millions and even billions of years for this process to happen.  Well, the star formation happens in just millions of years. But we can't watch it in process. So how do we know what's going on here?  Well, what we benefit from is millions of stars that we can look at.  And for those millions of stars, some of them are in this earliest stage, some of them are in their middle life, and some of them are in their end stages. 

It's kind of like if you were some alien creature sent to earth, and you had to report back to your alien boss, you know, what is the lifecycle of a human being, but you could only visit the earth for like two hours.  Well, you can't follow a child as it's born and watch it grow up and go all the way but what you can do is take a snapshot of all the people on the planet, and you see that a small percentage of them are tiny, miniature things wearing diapers, and there's more that are slightly larger running around being fed by their grownups, and then there's this huge chunk of them that are full grown adults.  And then there's this other chunk, that are that are maybe older, not able to care for themselves.  And maybe there's this tiny sliver who are in hospitals and about ready to pass on.  

And so you see then a cross section and by looking at that cross section of the entire population, you can piece together the lifecycle, what happens, and that's what we do for stars.  So we begin with this stellar nursery.  But we can see a stage in this process really cool.  So the second picture in the gallery shows another example of a stellar nursery, the Orion Nebula.  But using the Hubble Space Telescope, they've been able to capture detailed pictures of some of these earliest protostars.  And what they see around these stars, you can see the zoomed out boxes are disks, like dark disks of material around the star. 

So as these clouds are collapsing, they're also spinning, spinning around, and just like when you throw a pizza in the air and spin it, when something spins, it flattens out.  And that's what happens to this gas and dust.  So this material, that's the very beginning of the planets in this solar system.  In fact, we call it a proto planetary disk.  So as the star is forming that solar system, those planets around the star are also forming. 

Now, here's what's so exciting to me.  Now, as a Christian, we can look at this and we could say… you could say whatever you want.  But here's the amazing thing.  As we reflect on our solar system and we think about God making and crafting our solar system, and as we read in Genesis of God speaking and it happening, and we think about God, shaping all of these places, the Moon and the Sun and the Earth, when I look at this picture, we're seeing it happening, like, God is still doing it.  And the way I think of this is God is still speaking it, He's still saying, He's still saying, “Make this planet, make this moon”.  And, it's happening.  Because the universe has no choice but to listen to God; He is the maker. 

And so it's not like God made the universe a long time ago and then he just kind of kicked it forward and let it run on its own.  That's not at all the way it works.  God is continuously creating because our universe, throughout our universe, new things are continuously being made.  And if you have any doubt of this, all you have to do is think about your own child, or ask a friend who has a child. And my wife is pregnant right now. She's due this summer. And right now that baby is being woven together by God in her womb.   It's incredible.  God is One who continually creates.  And we can see that in the deep reaches of space, or I can see it in my own home, even as my child, I mean, my son who's four years old, when he's eating peanut butter sandwiches, that material is turning into his flesh.  God is still creating him.  What about me?  The air I breathe, the water I drink is becoming my flesh.  God is still creating me.  This is too profound. Well, I went too far.  But it's really amazing and cool.  Okay, so we can see stars in this beginning birth, how they first started. 

Let's look at the middle life of stars.  And I'm going to show a graph.  This is the third picture in the gallery.  And this is, without question, the most important graph in all of astronomy.  It's called an H-R diagram.  And what it does, it's meant to illustrate the groups of stars.  We’ll digest this chart.  But the H-R diagram, if you were in a typical, traditional astronomy class, the professor who's like way too into the nitty gritty details would spend like a week or two weeks on just this chart.  Like to an astronomer who does like astronomical research, this is so incredibly important.  To me, it fits in the big picture.  But I don't want to get lost in all these details. 

And here's the big picture of this chart.  We have to always… whenever you look at a graph, you have to look at the axes to see what is this actually graphing?  Well, it's graphing temperature, but it's doing something kind of weird.  Normally, you think it increased that way (left to right), but on a H-R diagram, it increases the other way (right to left). So colder temperatures are on the right, warmer temperatures or on the left.  And then the vertical axis is luminosity, or brightness.  We talked about luminosity is like the intrinsic brightness of a star or an object. Now just think about that for a second; how bright something is and how hot it is. That's what this chart is showing.  We've talked about this before, and we keep coming back to this, this notion of Wien’s law, when something is hotter, it's bluer, and it's brighter.  We keep coming back to that.  That is what the H-R diagram is showing us. 

So what you see is, if you were to take all the stars you observe in the sky, and you were to put them on a graph of the temperature, and the brightness, then you would see a graph that looks roughly like this.  And so we have to make sense out of.  Most of this graph makes sense but there's a couple things that don't make sense that we have to make sense out. 

Okay. The first thing is that you'll notice on this chart, that color is connected here, because color and temperature are related.  We've seen that; when it's hot, it's blue, when it's cold, it's red.  And so you'll see that the temperature scale is color coded.  But the other thing you'll notice is that the vast majority of the stars follow along this diagonal line, which is called the main sequence.  And this is where stars spend the majority of their “life”.  When a star ignites, starts fusing hydrogen into helium, when it starts that process and it burns that fuel, it spends its life just parked right there on the main sequence.

Now, where are you are on the main sequence depends on how hot you are and how bright you are.  I mean, the key though is that those two things are connected.  If you know either one of those, you basically know where you're at, because the hotter something is… I can hear you saying it with me, right?... The hotter something is, the bluer and the brighter it is.  So as a star, if the star is a medium temperature, like our Sun, it's about 6000 degrees Kelvin, okay, so it'd be right here, and according to Wien’s Law, we should know basically how bright it would be because a star is basically this black body, which follows Wien’s Law.  And so it would be right about here - about one solar luminosity.  We're measuring everything relative to the sun.  

If another star happened to be way hotter, like maybe 30,000 Kelvin, then it's going to be way brighter and it's going to be way up here on the graph, in the upper left corner.  So the question mark, though, becomes, well, what determines whether a star is hotter or colder?  What's the factor there that matters most?  And the answer is the mass of the star. 

So here's the picture, the analogy to have in mind.  A star in many ways, is like a campfire.  When you build a campfire, you put a bunch of wood on it, you light it, it ignites, that burns up, that fuel eventually runs out of fuel, and it kind of collapses and becomes ashes.  But have you noticed when you build a really small fire, it kind of simmers and stews for a long time.  It has a low mass because there's not a lot of wood on it, and it's a small fire; it's not as hot, it's not as bright.  

But if you were to build a big fire, and you put a lot of wood on it, you built a beautiful fire that could just ignite, huge, the more wood and fire, the more wood you have on there, the bigger the fire, the brighter it is, the hotter it is.  The same idea is true stars.  The more fuel you have, the more you mass you have, the bigger and hotter and brighter your star is. 

Now this analogy is a really good one because as you probably know, too, as with campfire, if you have a lot of wood on there, it's going to burn fast.  If it's hot, and it's big, you're going to burn through that wood really, really fast.  Whereas if it's a small fire, the log might take a long time to burn because it's not so hot.  It's not such a big fire. The same is very true of stars.  

If you are big, bright star that's hot and super luminous, you're actually, even though you're more massive, you're actually going to die earlier.  You're going to run through your fuel faster than if you are on the other side of H-R diagram.  If you're a low mass star, you're cooler, you're not as luminous, and you're going to go more slowly through your fuel.  And of course, the Sun is somewhere in the middle.  It's not like the perfect middle; it's just an average star.  Okay, our star is going to last a while.  It has lasted a while; it's going to continue to last a while.  

But there's something we’ve got to make sense out.  So far, everything in this makes sense.  I mean, this diagonal across here is Wien’s law.  That's just what it is.  But there's two things that don't quite make sense.  We have stars that are in the upper right corner of this diagram called giants, and we have stars in the lower left called dwarfs.  We’ve got to make sense out of these a minute.  Because what we have here in the upper right, these giants are stars that are cool, they're cooler, but they're still very bright.  And this doesn't seem to follow Wien’s law.  And on the same token, the dwarfs, they are really hot, but they're kind of faint, they're still blue, but they're kind of fainter. They don't follow Wien’s Law.  They’re fainter than you would expect. And the clue to answering this is those words giant and dwarf, because the brightness or luminosity of a star depends on temperature, definitely depends on temperature, but it depends on something else and that is the size of the star.  

So if you have a really, really big star, a big diameter, okay, it could be kind of cooler, but look brighter, because it's just so big. It’s got a lot more area shining. And by the same token, if you have a small star, a dwarf star, it could be very hot and so it should be very bright, but it's so tiny that there's just not a lot of area to be giving off much of that light. 

Now, how are these things all connected? It turns out that these aren't just different categories of stars that have always been giants, or have always been dwarves, but these are stages in the death of a star.  

So a star will start, like our Sun here, will start and live the vast majority of its life on the main sequence following Wien’s Law, but as it runs out of fuel, as the campfire starts to die, the star actually kind of bloats upward, bloats outward, and then eventually collapses.  And as it's bloating outwards, it's getting bigger and bigger and bigger, and it's moving into that upper right corner where the giants are.  And then as the star collapses down, the core, the ashes left over from that campfire, they're really hot, but they're really small.  So it drops down into these white dwarf areas. 

Okay, so a given star can change and move around on this H-R diagram, especially towards the end of its life, when it moves to be in the giant area, and then suddenly drops down to be in the dwarf area.  And what we're going to do is look at some examples of those, especially that end of life where that dwarf part comes in. 

So as the star is kind of expanding outward towards the end of its life, kind of bloating outwards, something happens after it's gone through that giant phase. And as it's collapsing, this is where the campfire analogy works again.  It’s such a good analogy. When a campfire is at the end of its life and it's ready to be done, remember what it does?  The wood can't hold up anymore, and it collapses down.  And what happens is a bunch of sparks fly out into the air.  It collapses down but there's stuff that flies outward while the collapse is happening.  So you get the ashes collapsing down while a bunch of sparks fly out, and that is so much like what happens to a star. 

The fourth picture in our gallery shows the Ring Nebula. This is what's called a planetary nebula. Unlike the nebulas you saw earlier on, which were star forming places, this is a star, a single star that has died.  And these beautiful colors, this ring of color, are like the ashes…  not the ashes… they're like the sparks that have flown out into space.  These are the outer layers of the star that are blown out into space as the middle of the star, the core has collapsed down, the ashes of the star have collapsed down, and you can actually see that blue star right in the middle of the Ring Nebula that is a white dwarf.  That is the leftovers of the star.  It's still shining.  It's blueish, not as bright and that's like the core of the remnant of this star. 

Now one of the cool things about the Ring Nebula is that the colors we saw earlier in an earlier video about how the spectrum of this can tell us about what materials are here.  And the color is actually telling us that too.  We see a layer of red, that's the hydrogen, we see a layer of green, that's like oxygen.  And so we actually see there are layers of material, different elements that were inside the star before it exploded.  And so this gives us a clue as to what's happening inside of stars.  We can't probe inside stars, but we can look at the aftermath after a star has been smashed out into space.  We'll look at that in the next video in more detail. 

The other thing that's really amazing and powerful here is that these materials that now fly out into space can be used again.   And this is that living parable that our bodies, in a sense, are going to reach the end just like the stars reach the end.  But our spirit is going to continue; there is new life after this life that we live.  And in the same way, these atoms and elements are going to go on and then collapse back down and be the next generation of stars.  And so these elements get recycled over and over again in every new generation of stars.  We're going to see how important that is for life on Earth in our next video. 

Okay, so a planetary nebula is one way that we can see a star die.  But if it's an even bigger star, like, this is what will happen to our Sun.  It'll blow out into a red giant, have a planetary nebula with material flying out, and then the core will become a white dwarf.  

But for a bigger star, it will have a tremendous explosion called a supernova.  And we'll learn about that as well when we look at galaxies, but a supernova is this huge explosion, incredibly bright, can be seen on the other side of the universe.  And what it leaves behind is this, you know, like, again, kind of sparks all this material flies out and it's called a supernova remnant.  

It's another beautiful kind of nebula that we can see; it looks very different, a supernova remnant.  But it also leaves the elements, leaves the ashes behind in a tiny little star, super small, that's called a neutron star, a neutron star, which are crazy, weird objects that were only discovered like 50 years ago.  And we're going to learn more about those shortly as well.  And again, though, these clouds is where the next generation of stars forms from. 

Okay, so we've seen this big picture, we've covered a lot of stuff, a lot of stuff, going from the very beginning of a star's life in these stellar nurseries, these star forming areas, living its life out on the main sequence, and then eventually dying a spectacular death through a planetary nebula becoming a white dwarf like our sun is going to do, or perhaps for a big star, blowing out into a supernova and then having a neutron star left behind.  So there's tremendous variety that we've seen. 

Okay, cool. We'll see you next time.