Placeholder Image

Subtitles section Play video

  • >> Thank you all for coming. I am very pleased to introduce Prof. Raja GuhaThakurta. He's

  • a professor of astronomy at UC Santa Cruz and he's an expert on galaxy formation and

  • Andromeda. And he's going to give us a talk about our place in the cosmos today. He's

  • also started a innovated program for high school students to do research at UC Santa

  • Cruz this summer and he's going to talk a little bit about that towards the end of the

  • talk. So I'm trilled to introduce Raja. >> GUHATHAKURTA: Thank a lot Jeff and thanks

  • Boris. Can you hear me okay at the back there? Okay, great. And thank you both for setting

  • this up. In fact, the high school program that Jeff mentioned is the exact reason for

  • my connection to Jeff. His daughter is in this program. So, I'm going to talk about

  • that at the very end. And I see a bunch of high school student, I see a bunch of middle

  • school students here, right? Middle or elementary? >> Elementary.

  • >> GUHATHAKURTA: Elementary. Even better. Good to start early. So, I'm going to talk

  • about galaxies today but I want to explain why it's important to talk about galaxies.

  • I'm going to explain why I study galaxies. And, so the title of today's talk is, "Our

  • Place in the Cosmos." And what I want to do is explain why, you know, why galaxies have

  • any connection at all to you and me. By way of, you know, giving credit where it's due,

  • these--many of the slides you'll see today, most of the narrative you'll see today, was

  • put together with the help of one of my colleagues at the UC Santa Cruz Astronomy Department.

  • Her name is Sandra Faber. Sandy has been studying galaxies for 30 years, she's one of the world's

  • experts in study of galaxy formation and evolutions. I've had the privilege of working with her.

  • We've worked together to keep this narrative current. As the years have gone by, we've

  • adapted our story to new findings. We've adapted the images and animations to new findings.

  • So, I hope to give you a little bit of a tiny flavor of the kind of galaxy research that

  • goes on at Santa Cruz and around the world. So, I wanted to put in a little bit of a disclaimer

  • also, that astronomy and cosmology are often confused with astrology, gastronomy, and cosmetology.

  • And I just want to set those three topics aside. They actually rear their ugly head

  • more often than I care in my studies especially when people find out I'm from India and I

  • study astronomy, I always get asked about palmistry and telling the future. I know absolutely

  • nothing about astrology. I know a little bit about gastronomy, it keeps me alive. And I

  • know very, as you can tell looking at me, I know nothing about cosmetology at all. So,

  • but I'll--where they do rear their ugly head, I'll mention them but I, you know, this is

  • a good example of cosmetology rearing its ugly head, no pun intended. So, let me--let

  • me actually give you a little bit of a road map of where we're going to go with this--with

  • this narrative today. So, I'll start with our place in the universe, in the cosmos.

  • And, it turns out our place in the cosmos is directly linked to a concept that's best

  • thought of as recycling. Recycling of chemicals, recycling of the elements in the periodic

  • table but done by the cosmos. Not done by West Valley Recycling, it's done by--on a

  • much larger scale in the cosmos. And it's done inside galaxies. Galaxies are the cosmos'

  • recycling plants. Now, galaxies do a whole bunch of thing in addition to cosmic recycling.

  • They are also cannibals, they like to eat their own. They like to eat their children

  • in particular. So, nothing to be scared about, you kids. Your parents are not at all like

  • that. But galaxies, in fact, do this all the time. And I'll talk about how cannibalism

  • plays an important role in galaxies. So you can see, gastronomy is already rearing its

  • ugly head here. The formation of galaxies involves cannibalism but only in the late

  • stages of galaxy evolution. Today, there's a lot of cannibalism going on in the Milky

  • Way, in Andromeda. But in the early stages, you don't have cannibalism because there's

  • nothing to cannibalize. You need to have galaxies in place for them to cannibalize one another.

  • So, the early stages of galaxy formation actually involve other processes, and I'll talk a little

  • bit about that. The early formation of galaxies involves ripples in the fabric of the cosmos.

  • I'll talk a little bit about the processes that give rise to those ripple. It has to

  • do with quantum mechanics. It has to do with a phenomenon called inflation, not the economic

  • kind but the kind the universe does. And it has to do with gravity. So, I'll talk about

  • those things. And at the--at, you know, the end of the science part of the presentation,

  • what I want to emphasize is that astronomy is a physical science. So like everything

  • in the--in the sciences, it's evidence-based. So if I tell you a story, I have to also tell

  • you the basis behind the story. Why, you know, why do we believe the story, why do we believe

  • what we believe, not just what we believe. So I'll tell you a little bit about this evidence

  • and that really has to do with using telescopes as time machines to test theoretical predictions.

  • Okay, so I'll start with Our Place in the Cosmos. And if I could have the lights down

  • a little bit in the front of the room if possible because many of my slides have a dark background.

  • I don't know--if that's easy to do. If not, it's--things are pretty visible on this--on

  • this screen anyway. I just realized that many of my--you know, the night sky is dark. So

  • when I take pictures of the night sky, the background is dark. It's not my fault. It

  • really is that way. But Jeff, this is already helping a lot.

  • >> [INDISTINCT] >> GUHATHAKURTA: Yes. This is--this is good.

  • So, oh, this is even better. >> [INDISTINCT]

  • >> GUHATHAKURTA: Yes. Thank you. Thank you. So when I think of our place in the cosmos,

  • I think of my, you know, my favorite people up there, you might think of your favorite

  • people up there. So I am going to put up an example of who I think of when I think of

  • our place in the cosmos. You know, on the right is my--is my daughter, she was seven

  • years old at that time. And on the left is my newly adopted son at that time. Okay. He

  • was--he hadn't been groomed in a while, so I apologize for his appearance there. But

  • what is common to those two entities, you know, it's a form of K9 life and human life,

  • is our protein molecules. So my biochemist friends tell me that protein molecule are

  • the basic building blocks of life. Now if I were being absolutely precise with my language,

  • I should say protein molecules are the basic building blocks of life as we know it. Now,

  • we know of many forms of life here on earth, from the simplest viruses, they're made of

  • RNA, to the most complex mammals. DNA and RNA are examples of protein molecules. Enzymes,

  • hormones, these are all neurotransmitters. These are all important aspects of life and

  • it's fair to say protein molecules are the basic building blocks of life as we know it.

  • Protein molecules are very complex as this picture shows, but if we would extend our

  • definition of life a little bit, another way to write that phrase would be to say complex

  • molecules are almost certainly the basic building blocks of any kind of interesting life. So

  • if there is life outside the solar system, and you know there might be, we haven't discovered

  • it, we can only speculate about it at this point. But if there's life beyond the solar

  • system, the kinds of life we'd be most interested in better be rich, better be diverse, like

  • the kinds of life we see here on earth. Those are the kinds we'd be interested in. And to

  • have any kind of rich and diverse life, you can bet they would have to have at its--at

  • its basis some kind of complex molecule. Because complex molecules have lots of chemical bonds,

  • they are capable of--they have many degrees of freedom, they are capable of taking on

  • many forms. Those are the kinds of life forms that we'd be interested in. Now, so to form

  • protein molecules or to form complex molecules of any kind, you need atoms with lots of electrons

  • and protons in them. You need things that are not right at the beginning of the periodic

  • table but somewhat into the periodic table. In the case of protein molecule, those atoms--I

  • am highlighting carbon, nitrogen and oxygen, I'm leaving out hydrogen deliberately. Hydrogen

  • is actually formed in copious quantities early in the universe's history. Electrons and protons

  • are initially moving around too rapidly for them to be bound by each others electrostatic

  • forces. Because the universe is very hot in its earthly phases. Hot means high temperature,

  • high temperature means rapid motion. When electron and protons have too high an energy,

  • they can't bind stably because, you know, their collisions are too energetic for them

  • to be--to remain bound. So when the universe cools down to a certain point, about 300,000

  • years after the Big Bang, the first hydrogen atoms formed, and hydrogen protons and electrons

  • mate for life. They stay together for 14,000,000,000 years. Now, it's a little more difficult to

  • produce more complex elements like carbon, nitrogen, oxygen. Actually hydrogen, helium,

  • traces of lithium and beryllium, form early in the universe's history just through this

  • natural collisions of particles. But carbon, nitrogen and oxygen don't form that easily.

  • They are actually cooked inside stars. They are cooked, when I say cooked I mean through

  • nuclear fusion reactions, they are produced inside stars. So, you might look at this and

  • say, "Okay, all is well." You know, we know where the carbon and nitrogen and oxygen came

  • from because we live around such a star. We live around the star that's undergoing fusion

  • reactions [INDISTINCT] that's what you see on the right there. It turns out the sun's

  • atmosphere contains carbon, nitrogen and oxygen. You know very well that the earth certainly

  • contains C, N and O. You know, if you've been to a barbeque recently or if you're wearing

  • a diamond ring or if you are breathing, which you certainly are, you are taking in nitrogen

  • and oxygen. So these elements are present in abundance on the earth, in the oceans,

  • on the earth's crust. These elements are present in abundance. But there is a little bit of

  • a mystery here. The sun, even though it contains carbon, nitrogen and oxygen actually has no

  • business to contain them because the sun has not yet produce these elements through nuclear

  • fusion reactions. The sun is merely converting hydrogen to helium in its core. That what

  • gives the sun, you know, the--that's what gives helium its name. Helium comes from the

  • Greek word for Helios. The sun is merely converting hydrogen to helium, near the end of its life,

  • about 5,000,000 years from now, 5,000,000,000 years from now, the sun is going to cook helium

  • into lithium, beryllium, boron, it will get up to carbon, nitrogen and oxygen and then

  • die. Die in the sense it will stop nuclear fusion reactions. So about 5,000,000,000 years

  • from now, the sun will have some legitimate claim to some carbon, nitrogen and oxygen

  • because it would have cooked it within its interior. So what business does it have containing,

  • you know, having some of these elements today? Well, its business is, it is descendant of

  • other stars. And what I mean by that is there are other stars--this is a picture of a star

  • field--there are other stars that lived and died before the sun came into being. And I--what

  • I mean by died is these stars rapidly cooked these elements, nuclear--they went through

  • nuclear fusion reactions. They cooked all the elements up to iron in fact within their

  • interiors, through nuclear fusion reactions. It turns out iron has the--is the most stable

  • of the elements in terms of binding energy per nucleon. So fusion is favorable energetically

  • as long as you go up to iron. Beyond that, you don't produce elements through fusion.

  • You actually produce them in stellar explosions through neutron bombardment in supernova explosions.

  • So, but the point is the sun is not a first generation star. The sun was born well after

  • some of its ancestors rapidly cooked these elements in their interiors, carbon, nitrogen

  • and oxygen, and indeed, many other elements. And these ancestral stars, their ancestors

  • in the same way we have ancestors, these stars died before the sun was born. They were very

  • efficient cooks. They cooked all these elements within their interior, but they were also

  • very generous cooks. They die in a spectacular way. These stars explode when they died. And

  • you--what you are seeing here is a real picture of an exploded star as it looks a thousand

  • years after the explosions, so about a thousand year old explosion that you see over there.

  • So the stuff that was once inside the star, was once cooked inside the star, gets generously

  • dispersed into surrounding space. So the sun was born out of the dust, the stardust, the

  • exploded ashes of many, many, many stars. So, in the words of Crosby, Stills, Nash & Young,

  • "We are stardust." You know, and for the young ones among you, you don't know who Crosby,

  • Stills, Nash & Young are, they are not a law firm. They are a rock group. And they must

  • have known some astronomy because they knew exactly what they were talking about when

  • they said, "We are stardust." So indeed, if you look around you, your neighbor, the chair

  • you are sitting on, the stuff that makes up this beautiful building, all of these was

  • once cooked inside a star. Not the sun but some other star, that enriched the cloud of

  • gas and dust from which the sun and earth, and the other planets formed. So that's a

  • remarkable--that is actually a remarkable thing to think that our origins are spatially

  • quite large. That is our--the elements that make up our bodies come from a large region

  • within our collection of stars. Now, a collection of stars is what we had to be part of. And

  • a collection of stars is what we call a galaxy. Because if we weren't part of a collection

  • of stars, if the sun were alone, the nebula from which the sun formed were alone with

  • no other stars around it, there's a pretty good bet that we would be made of hydrogen

  • and helium today. Not any of these other elements. And believe me, a speaker who is made of only

  • hydrogen and helium is far less interesting than, you know, than I hope to be. Okay, and

  • indeed, an audience made of hydrogen and helium is far less interesting than you are. So this

  • particular picture is a picture of a galaxy. But some of you have already guessed that

  • this is not a picture of the Milky Way Galaxy because we live inside the Milky Way Galaxy.

  • We can't take pictures like this of the Milky Way Galaxy. What we do instead is we take

  • pictures of our siblings. This is our sister galaxy, she's our older sister. Well, at least,

  • a biggest sister, I don't know about older. But this is the Andromeda Galaxy. This is

  • my favorite galaxy in the whole world, as Jeff mentioned, and I'll talk about it in

  • some more detail. Now, it's worth pausing here for a little bit to reflect on what we

  • are doing here. We live in a world without mirrors. We can't see ourselves. You know,

  • we can't see our Milky Way Galaxy. Imagine if you lived in a--imagine, you kids, living

  • in a world without mirrors. It will take you much less time in the morning to get ready

  • and go to school. That would be a benefit. But the downside is you wouldn't know what

  • you looked like. You would have no idea. You would have to look at your siblings, you would

  • have to look at your neighbors to figure out what you look like form the outside. That's

  • what we do here. Another analogy might be living in a house that you can never leave.

  • You wouldn't know what buildings look like until you looked out your window and looked

  • at your neighbor's buildings. And that's what we're doing here. This is our neighbor, the

  • Andromeda Galaxy. And to give you a sense of scale, light would take a hundred thousand

  • years to get across this rectangle, a hundred thousand years. Light takes one second to

  • get to the moon, eight minutes to get to the sun, four hours to get to Pluto, four years

  • to get to the nearest star, but we're talking about a hundred thousand years to get across

  • this picture. Now, we live in a very average part of the Milky Way Galaxy. In fact, astronomy

  • is a very humbling subject because it tells you over and over and over again that you're

  • completely mediocre. You know, our planet is completely mediocre, our star is completely

  • mediocre, our galaxy is mediocre. And people speculate our universe may even be mediocre

  • because people talk about multiverses, not uni but multiverses. Ours may be one of many.

  • So mediocrity is the theme of astronomy but it's a good kind of mediocrity in this case,

  • okay? So we live in an average part of the galaxy. We don't live on Castro Street in

  • downtown Mountain View where there are lots of, you know, lots of people, lots of stars

  • close together. We don't live often in the Hills of Los Altos. We live in somewhere near

  • the Google campus perhaps. You know, it's the--pretty representative part of--part of

  • town. We're about 25,000 light-years from the center of the Milky Way Galaxy. Now, one

  • of the things our group has discovered, our research group has discovered over the years

  • is the Andromeda Galaxy is five times bigger than this picture would suggest. You know,

  • when we started our work, conventional wisdom was the Andromeda Galaxy went out about as

  • far as you see in this picture. But we've been studying stars far away from this--from

  • the center of this picture literally, five times further out than this picture shows

  • and we've been continuing to find stars that are plausibly associated with the Andromeda

  • Galaxy in the sense that they're the right kind of stars, they have the right chemical

  • mix, they have the right velocities, they're moving with the rest of the Andromeda Galaxy,

  • and so on. Okay. So, let me talk a little bit about that. I love this picture. This

  • is a Robert Gendler photograph of Andromeda and I was talking about how it's eating its

  • children. Well, here is one of its children, M32. Those are snacks only, those two, those

  • are breakfast and lunch up there. Lunch is at noon, you know, 12 o'clock. Right above

  • it. And if you look closely, you'd see there's a bridge of stars that--this--that's been

  • stretched out from that galaxy that's immediately above Andromeda. The process is very simple.

  • If, you know, if I were the Andromeda Galaxy and you guys were a satellite, or vise versa,

  • what happens is gravity is an inverse-square law force. Gravity pulls hardest on something

  • that's, you know, closest to you. So I would pull very hard on the front row, I would pull

  • less hard on the back row, and the, you know, people sitting in between would feel a force

  • that's somewhat intermediate between these two extremes. What that would do is it would

  • stretch out this galaxy by virtue of this differential gravitational force. That's what

  • Andromeda is doing to that galaxy up there. It really is a--this effect is called tidal

  • effect, this is exactly what we experience here on Earth. The--when the moon pulls on