Video Transcript: Spiral Galaxies

This is a galaxy, kind of like the Milky Way.  And it's actually the closest galaxy to the Milky Way.  So that's why it's a kind of special galaxy.  It's relatively large on our sky but just look at this picture a second and think about all of those stars that are making up this galaxy.  There's so many stars, we cannot see them.  Something like with an estimate, there's something like 100 billion stars in this galaxy; 100 billion!

Now, think about that.  I mean, all the people on earth, that's 10 billion people on earth.  Well, there's 10 times that number of stars going around this one galaxy.  And think about the planets that are going around those stars.  We saw these amazing planets are rings of Saturn, the moon Io, with its yellow volcanoes and spewing all kinds of stuff, and we reflected on how Jupiter must be this beautiful sight in the sky on Io.  We saw, we've seen this kind of stuff in our own solar system.  It's amazing to reflect on what unbelievable sights and beautiful things there may be to see in this galaxy.  

Of course, the view we get from Earth is amazing but just imagine all the amazing things that are in this galaxy that we have no clue we can't see.  It makes me think about God's creativity, but also like, why did He make this?  Who is this for?  He didn't make all that stuff that's there for us?  Who did He make it for?  Did He make it for us?  I don't know.  Did He make it for his own pleasure?  Are there other living creatures there that He is interacting with?  It's amazing to think about.  And I think, the lesson that I take away is, who are we to think that we understand God?  I mean, God has revealed Himself to us in His Holy Word and through the life of Jesus Christ, but He is beyond understanding.  How can we think that we fully understand God?  Boy, I don't know.  This is astounding to me when I when I consider a whole galaxy.  And then as we'll see, the universe is full of galaxies.  It's just mind boggling.

Okay, in this particular video, we're going to take a look at spiral galaxies in particular.  So there are many different kinds of galaxies.  The Milky Way is one type of spiral.  And so we're just going to spend a little time trying to understand spiral galaxies. 

The Andromeda Galaxy is a great example.  One of the really cool things about Andromeda is that because it's so close, relatively speaking, it's the closest galaxy even though it's 2.3 million light years away.  Because it's so close, it's actually really big on our sky but the only way to see it really well is by taking a long exposure picture.  So if you know right where to look in the sky, you can see this tiny little bright spot, like with just your eyes, you don't even need a telescope or binoculars.  But you'll only see just the brightest part, but you can actually see that.  It's kind of cool.  If somehow your eyes could be as sensitive as a digital camera, and you could see the entire Milky Way galaxy, when you look up at the sky, you would see you could see it right there in the sky, and it would be bigger than the full moon.  In fact, it would be as big as six full moons together side by side.  Imagine that.  Imagine if our eyes were that sensitive and you had six full moons side by side.  That would be huge on the sky. That's how big this whole galaxy is in our night sky.  Unreal.  So if you look at this through a telescope, like a big telescope, you only actually see a tiny little patch of the galaxy because it's so big in the sky.  

Now it looks like it's kind of oval shaped but actually what we see here is that this is tilted.  Our perspective on it is tilted.  So these galaxies, they're not two dimensional.  They're flat, but they're in three dimensional space so they can be oriented any different way.  And so the Andromeda galaxy here happens to be kind of at a bit of an angle, which is why it looks kind of elongated.  As you can imagine, this is kind of like a paper plate that you're just viewing kind of sideways.  Okay.  

But there are other galaxies too, we can see.  This is one of my favorites.  This is called the Sombrero Galaxy, another spiral galaxy.  You can see those strong dust lines, those arms in the disk. And again, we're viewing it kind of at an angle. Some of these galaxies are even viewed totally edge on, they just look like a line, because they're so thin.

One of the things I want you to notice though in the Sombrero galaxy, is that there are different parts to the galaxy.  There's the spiral arms and the disk that we see but notice in this particular picture, which is the second picture in the gallery, there's this kind of diffuse glow throughout the whole galaxy, all the way around, it's just kind of glowing.  And that's not a glare or anything; that's actually starlight, those are stars spread all around, giving off in glowing light.  We call that part of the galaxy, the Halo.  The Halo, which makes sense.  Like if we have a halo glowing above somebody’s head, that's the halo of the galaxy.  So there's kind of an anatomy to a galaxy with the different parts.  And by looking at different galaxies, you can kind of say, well, what are these parts?  Why do some galaxies have it, other galaxies don't?

Another awesome example of a spiral galaxy is the Pinwheel Galaxy, the Pinwheel Galaxy, M 101.  And this is again, a spiral.  Now the paper plate is being viewed face on.  So we see all the spirals.  It’s such an awesome view.

And one of the things you may notice about these galaxies is a lot of them have the name M and then a number, like M 101; or Andromeda is M 31.  And that M stands for ‘Messier’.  And that was an astronomer who was using an early telescope.  This is early on and he was hunting for comets.  Now the thing you need to know about all of these things is that when you look with your eyes through a telescope, they all just look like a fuzzy glow of white light.  You can't see any of these details.  I mean, remember how the drawings looked, versus the photographs, versus the digital pictures?  Well, we see all these digital pictures, you think this is what it's going to look like to your eyes, but it doesn't.  And if you looked at M 101 with your eyes, you would just see, you would really just see the brightest part of fuzzy glow of white light.  And that's what Messier saw.  And so he kept track of all of these objects that he saw; over 100 of them, and he wrote down their locations so that people who were hunting for comets wouldn't mistake them for comets.  

Now these objects turned out to be a variety of things.  Some of them are nebulas, some are planetary nebulas.  Some are like the stellar nurseries.  Some of them are galaxies.  Some are supernova remnants.  And so it's taken time for us to figure out what are all these different objects, but we still use that Messier designation, that M 101 number, to give it a name.

Very cool.  In fact, we'll see in a later lesson pretty soon here about the challenge of answering that question, what are all these fuzzy things that we're seeing through telescopes?  That was something that astronomers were struggling to answer just as photographic film was being invented.  And the way they answered it was pretty awesome. 

Okay, so the Pinwheel Galaxy, we’re viewing it face on, and we get all these different perspectives of the spiral galaxies, depending on how that paper plate is being oriented in the sky.  

Now, the question arises, we have these beautiful spiral arms.  Where do they come from?  Why do these galaxies have these spiral arms?  I mean, in principle, this galaxy forms, there's all of these stars orbiting a central location, maybe it all forms out of this huge, enormous cloud of gas and dust that collapses down and then all these little collapses happen, which form the stars. They are all orbiting the middle, but why do we get spirals?  Why do we get these beautiful spirals, because not all galaxies have spiral arms?  In fact, a lot of galaxies, most galaxies don't.  Only like 30% of galaxies have spiral arms.  

Well, this is one of the leading theories, really the leading theory, of how spiral arms form.  

Okay, so while you might get, each of these lines on the left, this is the fourth picture in the gallery, each of the circles represents like an orbit for a star.  And the idea here is that the star is orbiting, and each of the stars individually is orbiting the center of the galaxy.  But over time, because of the mutual gravity, what happens is these orbits start to kind of precess, or turn around, and so kind of the idea to think about is like, they're not all rotating at the same speed.  The stars that are closer to the center of the galaxy are going faster; the stars that are further away are going slower.  And so the whole system is like rotating, but not all at the same speed. 

And so because the inner stuff is rotating a little faster, and the outer stops rotating a little slower, there are places it's hard to read, you can kind of see it in the middle picture where you get a little spiral of kind of denser region, and then certainly on the far picture you can see where the spiral emerges where the orbits of the stars are closer together instead of being further apart.  Areas where it's a little denser, there's more stars, or less stars.  So what that suggests is that these spirals themselves are not real physical objects that are like orbiting like the blades of a blender, but that instead, stars are kind of moving in and out of these areas of more density, like these areas where there just happened to be more stars, because of this, what's called differential rotation or this, different speeds, that things are orbiting around the center of the galaxy. 

So it's kind of confusing, I didn't explain it very well.  So this we call the spiral… what do we call it?  Let me get it right… it is the spiral density wave model, because it's like a dense region. It's like a wave, because it like comes and goes and comes and goes.  And it's a model because we think this is how it works; we're not 100% sure.

The picture to have in your mind when you think about this, though, is illustrated in the fifth picture in the gallery, which is like a traffic jam.  When you're stuck in a traffic jam, as you drive, the cars slow down, maybe there's a lane closed in the highway, the cars slow down, but eventually they make their way out.  And that traffic jam kind of sits right there.  It's stuck right there, and even though the cars are continuously moving.  So some cars are moving in while some cars are moving out, but the traffic jam may be sitting still and may be moving backwards and may be moving forward.  They're kind of separate from the cars.  And the same way the spiral arms are orbiting the center of the galaxy, but they're orbiting kind of at their own rate because the stars are separate from the spirals.  So it's kind of crazy.  So, a given star is moving into a spiral and then out of a spiral over the course of time.  

Now we can’t watch this happening, so a lot of this comes down to modeling what we know about gravity, and how we expect these stars to be moving.  Because when you look at galaxies, even over the course of hundreds of years, they don't look any different.  They're moving fast, but they're so big that you can't detect that change in motion.

Okay, so there we go. There's a little bit about spiral arms.  Next time we're going to take a look at other kinds of galaxies.  Alright, see you next time.