NASA's Universe of Learning Science Briefing: Birth of Stars, Near and Far

Moderator: Anita Sohus

May 3, 2018

Coordinator: Welcome and thank you for standing by. At this time, all parties do have an open and interactive lines for today's conference. If you do not have a mute feature, it is Star 6 to mute on your line. This call is being recorded. If you do have any objections, please disconnect at this time. You may now begin.

Jeff Nee: Hello, everyone. I'd like to welcome you to this Universe of Learning telecon today hosted by the NASA Museum Alliance. Thanks to all of you for joining us and to anyone listening to the recording in the future.

Today we're talking about "Birth of stars, near and far." The slides for today's presentation can be found on the Museum Alliance and NASA Nationwide sites. As always, if you have any issues or questions now or in the future, you can email Jeff Nee of the Museum Alliance at

As a final reminder, please do not put us on hold even if you have to step away because some phones play holding music, which can disrupt the talk. Just be sure your phone is on mute so that no noises from your end interrupt the speakers.

If you'd like to do one final check that you are in fact muted, you may simply say your name into the phone right now.

All right. Great. If you can hold your questions until after all the speakers have gone, that would be much appreciated. We will have some brief time for questions at the end so make sure you have a pen and paper to write down your questions as we go, and remember to note what slide number you're referencing. That helps sometimes.

You can read the full bios of all of our speakers on the websites, but as a brief introduction, our facilitator today is Dr. Emma Marcucci who is an education and outreach scientist from the Space Telescope Science Institute. Emma, it's all yours.

Dr. Marcucci: Thank you very much, Jeff. And thanks again to everyone for being here. We're excited to bring you this briefing today. To get started, we'll go over our resources, or some of our resources.

Slide 2 So on Page 2, or sorry, Slide 2, I wanted to point out the Lagoon Nebula. Hubble had its 28th Anniversary a couple weeks ago, or maybe just a week and a half ago. And this was the anniversary released image.

It's very timely because this is an area of star formation. This is a comparison of the visible versus infrared light views, which we'll hear a little bit about in our first presentation.

The link or the URL on this website takes you directly to a pan and view, or zoom and pan. It's kind of like a 3D view of this nebula that's very fascinating. So, I encourage you all to go check out those videos and images.

Slide 3 If we go to Slide 3, this is our standard Wavelength list of resources. We do have, in Wavelength, a link to the Lagoon Nebula images, videos and [press] release.

Another project within the NASA's Universe of Learning, in which this briefing is one project, but another project is a celebrity education video. They just released yesterday a short couple minute video called "Think Tank, A Star is Born." This is a video that features Jerrika Hinton from "Grey's Anatomy" and "Here and Now" and Wil Wheaton from "Star Trek" and himself in "Big Bang."

And so that's a video that will be talking about the subject that we're going into in more detail today. They also have a video about the death of stars. So, if you're interested in the whole life cycle, I recommend checking those out.

We have a few lithos and activities that you might be interested in. And the final section of resources there are some extra resources that talk about star formation in nearby galaxies.

We'll hear just very briefly about that today, but we're not going to go into too much detail. So we wanted to provide some references that you could use to go into a little bit more depth.

Bryan, who is our last speaker today, will be talking about another Wavelength list which we'll go into in detail, but I just wanted to have it on this slide too in case you need reference to it.

Slide 4 So on Slide 4, you'll see the outline of our presentation today. We'll be talking about star formation close to home in the Milky Way. And then we're going to talk about star formation in the early universe, which is the very distant universe.

And then we will hear our resources. We'll have a chance for question and answers in between 2 and 3 and then again after our third speaker.

Slide 5 So going to Slide 5, I will stop talking and start introducing our first speaker, Dr. Solange Ramirez, who is a scientist working at the NASA Exoplanet Science Institute, part of the Infrared Processing and Analysis Center at Caltech.

Dr. Solange, please take it away.

Dr. Ramirez: Slide 6 Okay. Thank you so much. It's a pleasure being here today. I'm going to start on Slide 6 just talking about where do stars form.

So, in the interstellar medium in our galaxy, there are molecular clouds. And the star formation process actually starts with the collapse of a molecular cloud because of gravity.

And on the picture there on the [right], there is an image of one of these molecular clouds. So now what you see there, or what you don't see there, because it is a dark blob, it's a cloud that has a lot of dust. And the dust is obscuring the interior of the molecular cloud.

So, the question is how do we know what is happening inside the cloud and learn how star formation actually happens?

Slide 7 So in Slide 7, I'm showing you two pictures of the Orion Constellation. And the picture on the left, you see the visible light, which is the light that your eyes can actually see. So, if you look into the night sky, that is what you're going to see.

But there is also this infrared light that has wavelengths that are much longer than visible light that our eyes don't see. But infrared light has the ability to see through opaque molecular clouds.

So, in both of these images, you can actually compare what visible light can see and what infrared light can see. And you realize that areas where the Orion Nebula is, which is almost at the edge of the Orion dagger [hanging from "Orion's belt"], is much brighter in the infrared than it is in the visible. And that is a technique that we use studying infrared light to see inside these molecular clouds.

Slide 8 So a little bit of theory in starting on the next slide, Slide 8, goes through the process, a cartoon showing four different stages of the star formation and thinking on a single star.

So, we start with the material from the molecular cloud that, due to gravity, starts to collapse. So, the material goes and infalls and starts forming their glob.

Over time and because there is an angular momentum associated into this cloud, a disk starts to form and after a while the collapse is stopped and what we are left is a protostar. It is a star that has ignited and a disk that it has formed around [itself].

Slide 9 So, in the next few slides I'm going to show you real pictures of these four stages starting with Slide 9, where, again, I'm going to be showing a lot of these pairs, visible and infrared, to just help you understand that infrared light is actually a very efficient tool in order to observe the star formation.

So in the first stage, which is the core, is where the collapse starts. The cores are completely invisible, in the visible [wavelengths]. They are cold, but they do make most of their light in the infrared.

So, in the picture on the right, we see a red blob there. And that is the core that has started to collapse and is a star being formed.

Now most of the pictures that I'm going to be showing here, as it is there in the credit, has been taken with the Spitzer Space Telescope. It is still in orbit and taking good observations. And it's one of the telescopes that the Infrared Processing and Analysis Center, where I work, operates and generates data.

Slide 10 So moving into Slide Number 10, we are moving forward into the process of collapse. In this picture, we start seeing an object that is later on the formation stages where a disk and an outflow are starting to come up into the picture. The outflow appears as the core continues to collapse.

Slide 11 In the next slide, which is Slide 11, in the picture on the right, it's a composite, in fact, of visible and infrared where you can see that as the outflow disappears, its disk is apparent and the star has begun to ignite. What happens is because of the collapse, the core of the cloud that is collapsing becomes really, really, hot and then the star ignites.

Slide 12 Later on when the stars form, what we are left over is a star with a disk. And in this picture, in Slide 12, what I'm showing is that the start of the light has been obscured, either by a mask or other kind of techniques so we can actually see the disk that is left over from the star formation.

That is what we call a debris disk. What is important to understand is that this disk, it's where planets later on form. So, it is there, a link from where star formation processes influence the knowledge that we have of our own solar system, which is important as well to understand why it's relevant to understand star formation processes.

Slide 13 All right. In the Slide 13, I want to do a little bit of how actually the collapse is stopped. Because if gravity goes inwards and generates the collapse of the cloud, then in order to generate a star, something needs to stop this collapse.

So, what is happening at the center of this blob protostar, is that a star is born when it starts radiating, like our Sun. It emits light. That is what I said about radiation. It's light being emitted by the star.

This light actually goes outward and it's the radiation pressure that's going in different directions than the gravity is what stops gravity to continue working. And this is equilibrium between gravity and pressure is what makes a star stable.

Slide 14 In the next slide, which is 14, it's the idea of, okay, when the star becomes hot enough, what is really happening inside there? And what is happening is that it's nuclear fusion.

We have two atoms of hydrogen that collide, because it is very, very hot and dense, and forms one atom of helium plus radiation or light that comes out.

And that is what we see from many of the stars that we see in the night sky, and during the day, of course, the Sun. And this process, this nuclear fusion process, occurred naturally in the interior of the star because it is so hot and so dense that it's a natural nuclear reactor.

Slide 15 Now, in Slide 15, I show a picture of the Eagle Nebula. This is actually a picture taken from the visible, one of the earliest pictures that Hubble took.

And the point [of view] in here of what I've been explaining about a star and a core and the outflow is from the point of view of a single star. And it's the basic theory that we use to understand this process.

But in reality, the collapse, it's actually more complicated. And it may be inhomogeneous. It doesn't have this spherical structure, but it can actually form filamentary materials like this one here. And inside those filaments, there are actually cores of materials that are going to evolve into a star formation process and actually form stars.

Slide 16 Going forward on Slide 16, I am showing different pictures of the Great Orion Nebula with zooms on two different areas because stars actually form in groups. And that is also an interesting idea.

They don't form in isolation. There are these giant stellar nurseries all over in our galaxies where thousands and thousands of the stars have been born together and at the same time. One of the examples is the Orion Nebula shown here on the picture.

Slide 17 In the next slide, which is 17, I show an artist's concept of the Milky Way. Of course, we are inside the Milky Way. So, taking a picture from outside, it is very difficult. But this concept has been made with scientific observations in mind and interpretations.

And it tells us that our Milky Way is actually in a spiral galaxy. And there, there are shown the different spiral arms that have been identified with astronomic observations, and there also you can see almost on the center-bottom of the picture, where the Sun is located.

Now the interesting thing is that it isn't just the spiral arms where most of these stellar nurseries are located. And in this picture, you can almost spot there, where the bright parts are, and that is where the stellar nurseries are actually located.

Slide 18 In the next slide, which I think it is very interesting, this is actually a real picture, not like the previous one. This one is a real picture taken by the Spitzer Space Telescope where it is taken in a very large field of view, comprising one of the arms that was shown on the previous sketch.

In this particular one, I think it is interesting to show that in the same picture, we have three areas -- they are shown in the ellipses -- that show star formation in different stages.

So, the larger ellipse on the right is the younger of the three, where you can still see material from the molecular cloud because you see dark clouds and you don't see a lot of radiation yet. And that is a sign of very early stages of the star formation.

In the ellipse of the nebula, it is where most of the stars in that conglomerate have already ignited, where nuclear fusion has started to come and we see that it is bright and energetic.

And on the last bubble in the very left, we see now all the stars that have been born, that they are young. And most of the material from the molecular cloud has been dissipated.

And this is a very real picture that we can take from our own galaxy.

Slide 19 In the next slide, which is 19, which I believe is my last one, this is a picture taken through one of the closest galaxies to the Milky Way, which is the LMC, which stands for Large Magellanic Cloud.

And in there, on the right side of the image, we see a very red active region. And that region has a name. It's called 30 Doradus. And it is a gigantic area of active star formation.

So, we have been seeing things like from the very small scale from one star being formed going into the larger scale of what is happening in the nebula going into what is happening into the spiral arm of the Milky Way.

And I'm finishing with this one to show that the same processes of the star formation that we see in our galaxy actually happen in external galaxies. And with that I'm going to leave the floor for the next speaker that is going to address star formation in external galaxies. Thank you.

Dr. Marcucci: Thank you very much for laying that out and describing all of those processes to us. We will have one more speaker and then a chance for questions. So, as a reminder, if you need to jot down slide numbers and questions, please feel free to do that and hold them for one more speaker.

Slide 20 So starting on Slide 20, we have Dr. Steve Finkelstein, who is an associate professor of astronomy at the University of Texas at Austin. And he will be speaking about star formation in a different kind of way or in an area where we need to use different techniques. So, Steve, please take it away.

Dr. Finkelstein: Hi. Thank you. Thanks for being here, everyone. So, I will be talking about star formation in the early universe. And so, rather than a detailed physics of what's happening and how stars are forming, we're going to be looking at stars on a galaxy-wide scale.

Slide 21 And so, the first thing we need to deal with here is what is a galaxy, and so that's on Slide 21. And on Slide 21, the background image is showing an image you've probably seen before, that's the Andromeda Galaxy.

That's a nearby galaxy to our own Milky Way. It's the closest large galaxy to us. And it's what many people think of when they think of a galaxy, big spiral arms, maybe a yellow center and blue sort of disk surrounding it.

But galaxies, even in the nearby universe, come in all shapes and sizes. And so, the four images on top just show different versions of different types of galaxies.

The one on the upper right is an elliptical galaxy. This is a galaxy that is also big, but it's not forming any stars. It's done all its star formation activity. We call these sometimes "red and dead" galaxies because they're dead in the sense that they're not forming any new stars and their colors are sort of yellowish red.

In the upper left, we show what happens if you take two galaxies like the Milky Way and slam them together. You create a galaxy merger. Galaxy mergers are actually thought to be the predominant method to create an elliptical galaxy.

When you slam two galaxies together, much of the gas gets funneled into giant bursts of star formation. And then the galaxies don't have any gas left. And when they don't have any gas left, they can't form any new stars.

The image on the bottom is the Sombrero Galaxy, another famous one. And that's what happens if you look at a disk galaxy somewhat edge on. It does a look a little bit different even though it may not actually be different.

And on the bottom right, we have another famous nearby galaxy, M82, where that red light you're seeing there, that's emission from warm hydrogen gas that's being blown out of the galaxy. This galaxy is actually undergoing an immense starburst at its center.

And so, all of these are galaxies. They're gravitationally bound systems of stars, gas, dust, black holes, planets, perhaps life, at least in our own galaxy, hopefully in others.

Slide 22 But when we look back at the early universe, as I'm showing on Slide 22, this image is the Hubble Ultra Deep Field. Almost every single bright spot you see in here is a galaxy. There are a few stars, but most of them are galaxies.

If you look sort of towards the upper right, you see something that looks like it has spiral arms. It looks kind of yellowish in this color scheme in this image. That's a very nearby galaxy.

But all of the faint little specks in the background, those are extremely distant galaxies. And what that tells us, images like this, really deep images of the universe tell us, is that galaxies in the early universe look very different.

They're much smaller than galaxies today. They have a lot more star formation activity than the galaxies today, but they also don't exhibit the elliptical or spiral structure we see today. They're sort of more clumpy or maybe even just one clump.

Slide 23 And so Slide 23 is sort of the main question of my research, which is understanding how you go from these tiny little clumps or train wrecks in the distant universe to sort of glorious, grand design spirals that we have today.

And because the topic of the day today is star formation, I want to sort of tell you how we measure star formation activity in the distant universe and then within a few minutes from now, hopefully, you'll understand how that star formation activity changes with time.

Slide 24 All right. So, on Slide 24 we'll talk about how do we detect star formation? And a very key point here, we got into this a little bit in the previous speaker is that when new stars are forming and we can measure this in our galaxy, they form at all masses.

You just don't form one big star and one small star. You form some big stars and some small stars and some medium sized stars. And the number of big versus small stars that you get are distributed according to something called the initial mass function.

And by studying the masses of stars in our galaxy and nearby galaxies, we find that when stars form, you get a lot of low mass stars, a few medium mass stars and very, very few high mass stars.

And so, the plot on the bottom left shows the cumulative mass ratio. So, the bottom axis, the stellar mass, that's actually units of solar masses. So, one is the mass of our sun. And so, M stars, which are the lowest mass stars, they go from .1 solar masses to about .5 solar masses. They form about half of all of the stars that you would form in our galaxy.

So, if you take a big cloud of gas and form a bunch of stars, about half of that mass is going into M stars. Only about 10 percent of that mass is going into O stars. O stars are 20 to 100 times the mass of our sun.

So that's kind of interesting. So, you might say, well, if you form a bunch of stars, they might just look like M stars because most of that mass is in M stars. However, as the bottom right plot shows, high mass stars, or O stars, are so much brighter than the low mass stars that [O stars] outshine them.

This plot is showing us the contribution to the total flux where the very top of that axis is the total flux of a population of stars. And the purple line is that of the O stars, the most massive stars.

And so essentially what you want to take away from this is that purple line is always pretty close to the top axis here. That means that O stars, even though they only contribute about 10 percent of the mass, dominate the light.

At the very bluest wavelengths and the ultraviolets, they are really all of the light. But even in the infrared, they may still be -- what is that -- 60 to 70 percent or so of the light.

And so, what that means is that when you look at a galaxy that's forming stars, you're really seeing the O stars because they're dominating the emission. But we need to keep the lifetimes of these stars in mind.

Okay, massive stars live very short. They sort of burn bright and die young. Low mass stars live billions and billions, even trillions of years, for the lowest mass stars.

So, if you see an O star, you know that that star has to be young. They only live maybe 5 million years. So that means that that star has just formed. And so, you have discovered ongoing star formation activity.

If you look at a region of a galaxy and you don't see any O stars, you know that there hasn't been any star formation for probably more than 10 million years, if not longer than that.

So, to summarize, the O stars, they don't take up that much of the mass. But they are very bright and they don't live very long. So, if you see them, you know star formation is happening.

And so, one of the ways in which we measure star formation activity in the universe is effectively to count the O stars. We usually can't resolve the galaxy such that we can actually count individual stars. But we can measure the amount of light we get at these very blue wavelengths here, where O stars are really dominating the emission.

Slide 25 And so I'm highlighting this on the next slide, Slide 25, actually the same figure that you saw on Slide 24, but now I'm showing you a few different wavelength bands. The ultraviolet shaded in purple. The optical shaded in green. And the infrared shaded in red.

And you can see that the O stars, that purple line towards the top, they're always higher than all of the other lower mass stars, but the difference is really exaggerated in the ultraviolet.

When you see something in the ultraviolet, it's pretty much all O stars. A small contribution from B stars, but pretty much all O stars.

So now we don't really need to count individual stars per se. We just need to measure the amount of ultraviolet light. And as long as we know how much ultraviolet light one O star puts out, we can then figure out how many stars are contributing that total amount of light.

Once we figure out how many O stars are there, again, we know that they have just formed so we can figure out the star formation rate. Okay. So, we're going to measure star formation activity by measuring ultraviolet light. And I'm going to prove to you that this works with a local example on Slide 26.

Slide 26 On Slide 26, I'm showing you the Andromeda Galaxy, the same one I showed you at the beginning. The middle image is one you're probably used to seeing. This is that optical or visible wavelength. And so this is what you would see with your eye.

The bottom are infrared wavelengths and you can see it looks pretty smooth. When we look in the infrared, you see O stars but you also see some light from lower mass older stars.

But when you look at the top in the ultraviolet, all you see are massive, newly formed stars. And you can see they're very, very clustered. These are the star formation regions, just like the Orion Nebula in our own galaxy that we heard about in the previous talk.

So, we can measure the star formation rate of the Andromeda Galaxy simply by adding up all of this ultraviolet emission. And we find that it's something similar to our Milky Way. It forms maybe one or two solar masses of stars per year. So, kind of like one or two sun-like stars per year or maybe a more massive star every few years, something like that.

So that's how we do it today and that's how we can measure star formation today. There are actually a number of different ways in which we can measure star formation activity in the nearby universe. But this ultraviolet light technique is the one we use in the distant universe. And I'll show you why.

Slide 27 So if we move to Slide 27, when we move out to the distant universe there are a few things we have to consider. One is that the universe is expanding. This was discovered Edwin Hubble almost 100 years ago and that kind of old timey looking plot in the upper middle is Hubble's version of Hubble's diagram, which is showing the distance to a galaxy on the horizontal axis versus the velocity that that galaxy is moving towards or away from us on the vertical axis.

And pretty much all galaxies have positive velocities, which mean they're moving away from us. So not only are all galaxies moving away from us, the farther away a galaxy is, the faster it's moving. And that means all galaxies are actually moving away from each other.

And Hubble realized that this means that the universe is expanding. And you might say what does that have to do with it? And it has a lot to do with it because of the Doppler effect.

So, you may be familiar with the Doppler effect for sound where when a source of sound is moving towards you, the sound waves get compressed and the pitch of the sound goes higher. And when the source of the sound is moving away from you, the sound waves get stretched and the pitch of sound gets lower.

The same thing happens with light. It's being illustrated by the plot on the bottom here. If you take a light source and move it towards you, you perceive the light waves as being compressed and so that source looks bluer than it actually is to you and vice versa for something moving away from you. The light waves get stretched and it looks redder.

So, if we go back to Hubble's trusty plot here, it says everything is moving away from us. And so, everything should look redder than it actually is. And not only that because more distant galaxies are moving away at greater velocities, they are even redder.

They appear even redder to us than more nearby galaxies. We call this effect the red shift. So, the amount of red shift in a spectrum is proportional to the distance to an object. So, an object that is shifted more to the red is moving away at a greater velocity and so it's at a greater distance.

And so finally on this slide, the table on the right has red shift in the left most column. We call by the variable Z, means red shift. And I'm giving you some numbers. These are numbers that we like to use and astronomers have good intuition for these numbers.

What I want you to look at is actually the right most column. That's telling us what time we're looking at. Because light takes time to travel, when you look at a distant object, you're not seeing it as it is today. You're seeing it as it was at some point in the past.

And so, when we look at galaxies that are farther and farther away, or higher and higher red shifts, or greater Z numbers, we are looking into the past. And so today, right now today, we are at red shift zero.

And we are looking at no time into the past because we are today. But this right most column is actually time since the Big Bang. So right now, we are 13.8 billion years since the Big Bang.

If we look at galaxies at a red shift of 1, that means that all of the wavelengths of their light have been doubled. We're already looking to a time only 6 billion years since the Big Bang. So, we're already looking more than halfway into the past. And we can go so on and so forth down to Red Shift 10 in this table.

If you're looking a source that's at a red shift of 10, you're looking at a time only half a billion years or 500 million years since the Big Bang. And I will tell you, we can see galaxies at red shift of 10, just barely, with Hubble. And we're looking pretty darn close to the beginning of the universe here.

All right, finally, the middle column, this is the important one for the topic here, which is star formation, this shows us what wavelength does that ultraviolet light that we want to see actually appear at.

So, ultraviolet light has a wavelength of about 150 nanometers today. That's it rest frame. And as we move out in red shifts, that wavelength increases as the light gets red shifted.

So, at Red Shift 1 it appears at 300 nanometers. At Red Shift 2 it appears at 450 nanometers. That would appear blue to your eye. And so, what that means is that if you could see a Red Shift 2 galaxy with your eye, okay, you'd have to look through a pretty big telescope, because usually we use a camera attached to a telescope to see this.

The ultraviolet light from that galaxy would actually be detectible as blue photons to your eye. By the time you get out to Red Shift 4, those photons are shifted to be red photons to your eye at 750 nanometers. And at Red Shift 6 and beyond, they're shifted into the infrared.

Now Hubble, even though it's mostly thought of as a visible wavelength telescope, actually it does work into the infrared to about 1,600 nanometers or so. And so, I have this blue box showing Hubble's wheel house. This is where Hubble is really good at measuring this ultraviolet light.

So, to recap, we can count star formation, or measure star formation activity, by essentially measuring how much ultraviolet light is coming from a galaxy. But when we're looking at distant galaxies, we have to look first in the optical and then in the infrared to see this ultraviolet light because that light is getting red shifted.

Slide 28 So with that in hand, let's see some results. So, as we move to Page 28, I'm going to talk about this plot on the bottom left here. This shows the star formation rate activity as a function of red shift. And remember Red Shift 0, that's the left side, that's today. And Red Shift 5 is about 12 or 13 billion years into the past.

And so, the data here comes from the Hubble Deep Field. This is the image shown on the bottom right. This is a revolutionary type of observing program done in the 1990s with the Hubble Space Telescope.

It was the first time somebody had pointed a space telescope at a single place in the sky where it was thought there was nothing, and just let it stare for hundreds of hours. And it turns out it's filled with galaxies.

And one of the cool things you can do with a survey like this is you see galaxies at all kind of different distances or different red shifts. And so, you can measure how much star formation activity there are at all of these distant red shifts.

And so, the local measurement is this triangle. It's minus 4 in these units. Don't worry about these units. That's just some level of star formation. And you can see as you go out to red shift of 1, it rises. And so, the amount of star formation in the universe today is less than what it was in the past. That was a very important thing to learn.

I came into astronomy as a student after that was already discovered. So, I think that's natural. But why does it have to be decreasing at this point in the universe? Why isn't it still increasing?

So, we see that it does keep rising. And then it's actually hard to tell what's going on because the remainder of these data points, as the greater red shifts have all of those arrows on them, that means they are lower limits. That means the star formation is just higher than that arrow, but it's hard to tell.

So, if we want to do better, we need deeper imaging and really we need imaging in the infrared so we can push the higher red shifts. And that's what's shown on Slide 29.

Slide 29 Slide 29 shows the Hubble Ultra Deep Field. This was a new image taken with a new optical camera and a new infrared camera on the Hubble Space Telescope. And that allowed us to push these studies out to red shifts of 10 or so. And so, this is kind of a busy plot because I took it from a review paper of mine. And I didn't have a lot of time to take these datapoints out.

So, if you just look at the gray little circles. So, the gray little circles are sort of the lower red shift measurements. And you can see something similar to what I showed you on the previous slide from today, out to Red Shift 2 it's rising. But then we see there's actually a turnover. And we didn't know that before. It turns over and then it starts falling off.

And then just use those big blue circles to guide your eye as it goes down and down and down. And so, what we have learned is that today the star formation rate is lower than it was in the past, but there was a peak point. Okay. About 10 billion years ago, a red shift of 2, is when the universe had its peak period of star formation.

And then as you go towards even earlier times, it goes down again. To put that another way, the amount of star formation in the universe today is pretty similar to the amount of star formation at red shift of 7 or so, which is about 1 billion years after the Big Bang.

And so, the amount of star formation in the universe is actually on the way down. And why we think that's happening is we know that gas is a fuel for star formation. The universe starts with a certain amount of gas and it's basically running out.

Slide 30 Finally on Slide 30, I'll show you what we expect to find in the future. We've measured pretty well out to about a red shift of 10, but we would like to go to greater red shifts. But we have two problems right now.

One is that Hubble, while awesome, is not that big of a telescope. Its primary mirror is only about 2.4 meters, or about as tall as your typical NBA center.

The other issue is Hubble can't observe redward of about 1600 nanometers. And if we want to look at Red Shifts 12 or 15, where a lot of theoretical work implies there should be galaxies, we need a better infrared sensitive telescope. And that's where the James Webb Space Telescope will be.

The upper right shows you a schematic of how much larger its mirror, its 6.5-meter mirror, will be compared to Hubble. And it's also going to work in the infrared.

And this plot here, it's just similar to the plot on the previous slide, but it's showing what you can expect to see as we go out to Red Shift 10.

The purple curve and the blue curve are two different models that include lots of physics as their ingredients. They are theoretical models. And they match all of the data we've found. But they have very, very different predictions for what happens at higher red shift.

The blue model predicts that high red shift, very distant galaxies, are very efficient producers of stars. So, there should be lots of star formation activity. And the purple model I don't like so much because it's pretty pessimistic. It says we may not find so much.

And so, we can study which of these models may be correct or incorrect with direct observations of this time in the universe, of star formation in this time of the universe, with the James Webb Space Telescope.

Slide 31 So I'll just finish with a couple takeaway points on Slide 31. So, we can trace the star formation activity by looking for ultraviolet emission from bright high mass stars. Because these high mass stars are short lived, if we see them, if we see ultraviolet emission, that means that star formation is ongoing.

If we want to observe this ongoing star formation in the distant universe, we must observe red shifted ultra violet emission, which is in optical for modest red shifts of 2 to 5, and in the infrared for the most distant galaxies known.

And so, by studying the amount of star formation in galaxies at a range of distances, from today, or a range of times from today, we found that from early times, star formation activity rose at a slow but steady level.

It peaked about 10 billion years in the past. And this activity has since been decreasing at a pretty steady rate, such that the amount of star formation in today's universe is similar to that at a time when the universe was less than 1 billion years old. Thanks for listening.

Dr. Marcucci: Thank you very much for that description. So, we'll take time now for some questions. I'll please ask our audience to limit yourself to one question. If we have time and everyone asks their questions, you can ask a second one. If anyone has a question, please unmute and speak up.

Man 1: I just have a really quick question for Solange. On Slide Number 6, I might have missed it, did you mention what molecular cloud that is on Slide Number 6?

Dr. Ramirez: Yes. I can provide the name. I have it written on my desk. I'm not at my desk right now. It's one of the local molecular clouds.

Carolyn Slivinski: I actually looked this up, Solange.

Dr. Ramirez: Oh, you did. Okay, great.

Carolyn Slivinski: It's in the notes section of your PowerPoint slides now. And what I found was it said visible light images of the dark molecular cloud Barnard 68. Dr. Ramirez: That is correct. Yes.

Carolyn Slivinski: There you go.

Dr. Ramirez: Thank you.

Dr. Marcucci: Great.

(Adrienne): Yes. This is (Adrienne). I have a question for Dr. Ramirez. On Slide 18, you were showing the images for different points in time. And I'm wondering were those observations that showed those stages or how can you tell those are different stages?

Dr. Ramirez: So, in that slide, this is a large field of view in the spiral arms in this area that is called M17. And these are real observations from the Spitzer Space Telescope that they were targeting in survey mode in order to determine basic ingredients of the star formation along the spiral arms.

(Adrienne): So, the observations that are being made are real time, but they're showing that it's so far away and so long ago that we can see those different points? I'm just trying to understand how those observations show that difference.

Dr. Ramirez: So, the difference is because of the structure of the three different areas that it is very different. The one on the right, do you see that they have those dark clouds in there that, even at an infrared light, it is somehow obscured?

So that tells you that there is a molecular cloud material in there [i.e. stars have yet to ignite]. The one in the middle shows a bright [stellar] nursery. That is already something similar to the Orion Nebula where you are able to see actually young stars in that area.

So, you see that falls into the theory that we have that a younger star formation region has more molecular material that it is obscured and it is in this collapsed stage.

As the area becomes older, you see stars that are being formed. And you still see some nebular material left over, while on the very left side, that material has already been dissipated [it looks clearer].

(Adrienne): Okay. So, I'm trying to think of an analogy. So, it would be like if you had a room with people of different ages in the room and you could take a photograph in there...

Dr. Ramirez: That is right. That is actually a really good analogy.

(Adrienne): Okay. Well, you helped me understand. All right. Thank you very much.

Dr. Ramirez: You're welcome.

(Gordon): Hello, I have one.

Dr. Marcucci: Go ahead.

(Gordon): Gordon Houston, Solar System Ambassador. On Slide 14, you mentioned that the core of the stars is hot enough to become a nuclear reactor. Is it strictly heat that is the function of becoming a nuclear reactor or is there, like, pressure or gravitational collapse that creates enough heat in there?

Dr. Ramirez: So, it is the gravitational collapse of the material. And it's a combination of both temperature and pressure. It's the conditions of the gas.

When we think about temperature, in our experience, in our day, temperature is kind of fussy, right? We either feel like it is hot or when it is cold. But what happened at smaller scales is that actually temperature is related to the collisions that atoms are experiencing.

If the gas is very, very, very dense, then it becomes hotter because more of those collisions are happening in the cloud. And as part of these collisions, there comes a point where it's so, so, so hot that the collisions between two atoms actually makes them fuse together and create another element and light.

And that is when I said the core of the star, it is becoming hot enough to actually become a natural nuclear reactor.

(Gordon): Yes. But that's really a function of the pressure pushing those things together to create heat, right?

Dr. Ramirez: Right. Exactly. So, as I said, it's a combination of both, temperature and pressure of the gas. It's the whole condition of the cloud that facilitates this process of nuclear fusion to occur in a natural way.

(Gordon): All right.

Dr. Marcucci: In the interest of time, I'm going to sneak one more question in here and then we're going to have to move on. Steve, on Slide 28, you mentioned in that plot that those arrows indicated that those were kind of lower limits. Could you talk a little bit more about why those are lower limits and why there isn't - is that just because it's farther in the red shift?

Dr. Finkelstein: Yes. That's a great question. So, the main reason is you know how much star formation you see, but you don't know how much star formation you don't see.

And so, as we go farther and farther back in time, we're seeing brighter and brighter and brighter intrinsic galaxies. So, there are lots of bright galaxies but even more faint galaxies. And it's really, really hard to see those faint galaxies. And basically, we know that we don't see them, but we think they're there.

And so, what I believe these datapoints are is they just added up everything they saw. But there are lots of things that Hubble simply wasn't big enough to see. And so, they think the true value was somewhere above this actual datapoint.

Dr. Marcucci: Great. Thank you. If anyone has a question and who was unable to ask during this time, please make a note of it. And if you send it to Jeff, we'll coordinate with our speakers to get that answered.

Slide 32 In the interest of time, though, I would like to move to our final speaker of today, and that will be starting on Slide 32. Dr. Bryan Mendez is an education specialist at UC Berkeley's Space Science Laboratory and an adjunct professor of physics at Diablo Valley College. And he is going to talk about some educational resources that could be used in your venues. So, Bryan, please take it away.

Dr. Mendez: Slide 33 Thank you. And greetings, everyone. Glad to be here and help you think about ways that you can engage your audiences in the topic of star formation. And so, on Slide 33, I just remind you of the NASA Wavelength list that I created that is a link to many sources. All of these are NASA funded sources that you could use for your educational programming.

So, there's a range of them. Most of them you're going to see are probably image based. And I'll explain kind of why in a little bit. But there's a few things like some videos.

There's the brand-new video that's not on my list that Emma put in the top of the slide deck so you'll want to check that one out, too. But please do check out those resources as I think they will be very helpful to you.

So, let's look through a few. I'm not going to go through all of the ones that are on the list because there's a lot there. But I'm going to kind of pick some kind of categories of resources that you can use.

Slide 34 So on Slide 34, I'll start by just saying we can go to the NASA Web site and you can look for images. And, in fact, the link that I put in the Wavelength list goes - it actually is a search. And so, what it does is it searches the site for all images that are tagged as nebula.

And telling the story of star formation is really, I think, best done with images because star forming regions are among some of the most beautiful images that you're going to see out there in astronomy. And so, when you've got beautiful images, use them, right?

So, the one caveat that I'll put out there, and I'll kind of say this probably over and over again, is that when you do a search on nebula you do want to be careful because if you're just interested in the story of star formation, well, nebula come in a few different forms.

They're the sites of both star birth and star death. So, some of the images are actually dead stars you're looking at. So, an example here on the first few images that come up on the NASA search, you know, you get that beautiful Lagoon Nebula, which is the star forming region is the first one.

But then the Crab Nebula shows up there as the sixth image that comes up, and the Crab Nebula is actually a site of star death. That is a star went supernova over 1,000 years ago. So, it's worthwhile keeping track and reading the captions so that they can tell you what's happening in the images.

Slide 35 On Slide 35, I also have another link there that's going to take you directly to the Hubble site. So, if you want to look specifically at Hubble images, this will do that for you.

And, again, with the same caveat, it just searches on all things called nebula so make sure that you're reading those captions and seeing is this a place where stars are being born or is this a star that has died?

The types of the stars, and if you're looking for the key words, "supernova" or "planetary nebula," those are both sites of stellar death. And then the larger clouds that have the more wispy shapes, those tend to be our star forming ones.

Slide 36 On Slide 36, there is another collection. These are all - you're going to find a lot of the same images over and over again, but some of these collections give you additional amounts of information. And the Astropix collection is especially nice because they give you a lot of information about how the images were put together.

So, there's information about what wavelengths are being represented in the image and what do the colors mean. You've seen lots of beautiful pictures already today. And you've noticed there's all these wonderful colors. And those colors actually are somewhat intentional on the part of the people who have created them for public release.

Your eyes can't see nebula like these. Even if you're sitting in the middle of the Orion Nebula, you'll never see what our telescopes can see because your eyes don't have that level of sensitivity. And so, telescopes do what they do because they're so sensitive and they see more than our eyes can see.

But that means we have to translate the information that those telescopes gather into something our eyes can see. And so, when we do that translation, we do it often with color. And so, it's useful to understand what's happening, especially when it's light that your eyes can't see, like ultraviolets are infrared images.

And so, the Astropix collection gives you information about what wavelengths are represented and which wavelengths are translated into which colors.

And that will tell you a lot about actually what's going on in the image. And a lot of the infrared images that you see from Spitzer or from the WISE Telescope -- I was a part of that mission -- we colored coded them so that you often knew certain types of dust were green and other types of dust were red. [And those two different colors not only told you what types of dust it was, but also tells you what the relative temperatures of the dust were. And so that can be useful in understanding the image.]

Slide 37 On Slide 37 is a page that if you have your audience members for a longer period of time and wanted to engage them in some kind of longer learning activity, one resource to do something about a deeper understanding of the images that we get of these nebulas comes from the WISE mission.

And it's an activity that will lead you through actually going to the Web sites over there at Caltech, actually, where they keep a lot of the infrared data, downloading those data, and then using the data to actually construct your own pretty pictures as I call them because that's what they are. They're pretty pictures but they also tell you a wealth of information.

And so, the activity is about learning what is a digital image? How does it work? And how can I create my own versions of some of these beautiful pictures that you've seen come out from NASA?

Slide 38 On Slide 38, another resource that's worth knowing about then so you could, you know, get the images, the raw data that have been taken by the space telescopes themselves, or, you could have a telescope, a robotic telescope, take you your own images and then construct color composites from those.

And that's what the Observing with NASA Program does. They operate a robotic telescope that's in the Arizona desert, I think. And on a daily basis, you can make requests of certain images for the telescopes to take for you the next day.

If it can, it will observe the objects that are available to it and the next day, it will tell you, hey, I have observed them. Here you can come download them. And then they provide some tools that allow you to go ahead and put together those images, manipulate them and even make your own color composites.

So, again, this is if you're in a situation where you have learners for a longer period of time and are able to engage them in a deeper way.

Slide 39 On Slide 39, I kind of feel like the progression is going from showing people pictures to them making their own pictures to them just getting to just see these things with their own eyes.

And so, if you're able to host a star party, for example, one of the things you could do is a nice activity from the Night Sky Network where it's a treasure hunt.

You have several telescopes that will point to different nebula in the sky and maybe they're at different stages of star formation or the entire star life cycle and it becomes kind of a treasure hunt for a family to go from one telescope to the next and say, okay, yes, a star is forming in the Orion Nebula. And, oh, and I saw a star dying in the Ring Nebula. And they get to go through that little activity of finding their own stages of life.

Slide 40 And then finally on Slide 40 is another example of some research where you can really do a deep dive. You want to learn all you can about the stages of life for a star. There's some really nice materials.

The one that I'm showing you on Slide 40 is from the Chandra Education Group. And they have a really nice activity set that has textbook level information on star formation and stellar life.

Slide 41 And then they also have some really just nice graphics. So, Slide 40 shows a nice graphic that was made by the Night Sky Network that you can actually print as a poster that kind of shows the whole entirety of the stellar life cycle showing that these star forming nebula are kind of the beginning and actually even the ending of the star forming cycle.

So that's my quick rundown of some resources. And if you have questions about further ones, feel free to contact me and do check out the Wavelength list.

Dr. Marcucci: All right. Well, thank you very much, Bryan. I would like to give a few minutes for anyone, if anyone does have a question right now that they'd like to ask Bryan.

It is the bottom of the hour, so if anyone needs to leave, we understand that. Thank you very much for attending or participating. And if you have questions, you can send them to Jeff. But does anyone have a question for Bryan?

Man 2: Bryan, just a quick question about your image processing lesson. What age range would you recommend or is it targeted for?

Dr. Mendez: So, for the WISE one, actually both the WISE and the (OWN), I think those are targeted at kind of that middle and high school level. And they work great with adults, too.

Man 2: Great. Thank you.

Dr. Marcucci: Thank you. Any other questions. Oh, yes. Go ahead.

(Gordon): This is (Gordon) in Houston, Solar System Ambassador. I just wanted to say hi to Bryan. I attended the 2012 Mayan seminar in Houston.

Dr. Mendez: Oh, fantastic.

(Gordon): And then I don't know, is Steve in there still?

Dr. Marcucci: He had a meeting at 3:30 that he had to run to so he actually had to jump off. But if you would like to be in contact or have questions, we can coordinate that.

(Gordon): No. I saw him at the (Frank Bastia) Symposium at UT some years back, too. So, I think he was a post-doc tech at Tech (unintelligible). Okay. Thank you very much.

Dr. Marcucci: Slide 42 All right. Thanks. All right. So, any final questions? All right. Well, hearing nothing, I will just wrap up with our final slides. Slide 42, if you're not aware, we have another professional development opportunity.

They have spent seven webinars going over all of astrophysics. Those completed yesterday, but they are archived. If you're interested in that community of practice, the URL is here on the Web page.

And having completed these webinars, there is an opportunity for many funding resources.

Slide 43 On Slide 43, our last slide, as always, we are interested in serving your needs, meeting your needs. As such we do evaluation for the science briefings. If you would like to opt out of participating, please contact (Kay Ferrari) for that.

As a note, this is our final - sorry. So, for the NASA Universe of Learning Science Briefing, this will be our last one for a couple months. We'll be taking a break in June and July. We'll see you again in August. And we will be taking this time in June and July for this evaluation time.

So please keep an eye on your email. You may see something in the next few weeks about this process.

Thank you again to all of our speakers and our attendees. I will pass it back to Jeff for final comments.

Jeff Nee: All right. And, of course, thank you to Emma and all of the Universe of Learning Team and our speakers. Remember that all of our talks are recorded and posted on the member Web sites. And you are encouraged to share the presentations as professional development with your colleagues, including your education staff and your museum docents.

If you have further question about this topic either now or in the future, like Emma said, always feel free to email us. Again, this is Jeff Nee of the Museum Alliance. And my email is

As always, the most up-to-date information for our future telecons will be on our Web sites and I hope everyone has a wonderful weekend and may the fourth be with you.

Dr. Marcucci: Very good. Thank you.

Woman 1: Thank you. You, too.

Jeff Nee: Bye, everybody.

Dr. Ramirez: Thank you so much.

Dr. Mendez: Bye-bye. Thank you.