IYA Unveiling Moderator: Anita Sohus October 6, :00 pm CT

Transcription

1 IYA Unveiling Moderator: Anita Sohus October 6, :00 pm CT Carolyn Slivinski: Just a reminder too that if you are listening in please use your mute but not your hold button, because there are a lot of hold buttons that play music, and it would be a little bit of a cacophony here. So the star 6 will mute and unmute for your phone. So today we're going to talk about the science background for the image that will be unveiled in November. So we'd like to welcome all of you whether you're librarians - libraries or planetariums, science centers, museums, schools. We have a real nice mix here so hopefully everyone will have something to learn. And now I'm going to turn this over to Frank and he's going to start the presentation and I hope you've all gotten onto the Website and downloaded either the PDF or the PowerPoint so you can follow along with this. All the slides have been numbered so we will do our best to let you know exactly which slide we're on all the time. So I will turn it over to Frank. Frank Summers: Good afternoon everybody. Welcome to the longest title I've given in a while, Great Observatories Galactic Center Region Image Unveiling Science Telecon. Yeah. Yeah, there we go. That's quite a mouthful. But basically if we go to Slide Number 2 we're talking about here is where we're doing multiwavelength observations from NASA's Great Observatories and we're giving it to you to release next month. If you go to Slide Number 3 you can see the main panel that we are releasing. This is the galactic center region and you'll understand this image a lot better by the end of this telecon. This is what we call the composite panel or Panel A in our terminology around here. It is a composite of the Hubble, the Spitzer and the Chandra images all put together so you're

2 seeing with, you know, Hubble's view and Spitzer's view and Chandra's view all at the same time. And you can see in the lower right hand corner the three individuals of the Hubble/Spitzer/Chandra that go into making this composite. Our second panel is on Slide Number 4. And this we call our Panel B or the trio panel. And this breaks out those three images. You'll notice that the three images we show here are cropped a little bit closer, they're a little bit - not as wide as they are in the A Panel, in the composite panel. Well basically the reason for that is that Hubble did not have the full area coverage that Spitzer and Chandra did so to make the Hubble image look good on this triple panel we had to actually crop it down just a little bit tighter. I know that's unusual saying we had to make Hubble look good but this is the galactic center region and I actually think Spitzer has the best view of the galactic center region, not Hubble. I know that's sacrilege for speaking that here in the Space Telescope Science Institute but unfortunately for this it's true. And this is the one that has the text on it that people can read and gives you the details. At the very top we have Axel Mellinger's view of the Milky Way. This is a visible light view of the Milky Way since even Hubble in this triple panel is viewing in the infrared. So that's sort of a reference for what the Milky Way looks like in visible light. And I'll give you some more detail about it in just a minute. Just to remind you on Slide Number 5 where you downloaded this PowerPoint is our support Website. And soon, real soon, this week, right, or next week, all right - Denise doesn't want to promise it until next week - next week we've promised that we will have up a generic press release which you can send out to your media telling them to come to your - about your - generic media alert that you can send out to your TV stations and your radio stations to have them come and cover your events that you are doing in November.

3 These are generic so you fill in your name, fill in all those details about your region but we just give you a sort of a template that you can work with. We also will have an image caption for the composite image, that Panel A. It doesn't have any text on it except for just the name and so we have a PDF file that you can print out and put on, you know, foam core or something like that, and mount next to the image so people can read about that image and help understand it. Again those will be posted by sometime next week. Denise Smith: You're writing that one. Frank Summers: Yes I know I'm writing that one. Denise is looking at me going okay I'm not promising that. Yes, I'm promising that but we're not promising it until next week. Let's see, Slide Number 6, let's go into just the basics of the three different telescopes because a lot of your visitors will ask you about the telescopes. And so Hubble was the first of the Great Observatories - well the three Great Observatories we're talking about today, that was launched. It was launched in April And it's a normal telescope using a reflecting mirror that does visible, ultraviolet and infrared observations. So it doesn't just do visible light, it also does some infrared and some ultraviolet. And there are the wavelengths in nanometers if you're interested. The mirror is 2.4 meters across, so that's what, eight, nine feet, all right. So it's really, you know, it's human sized with your arms stretched out and standing on tippy toe. Okay so that's a pretty big mirror but much smaller of course than say the 10 meter mirror of the Keck Observatory on the ground. You can build much bigger mirrors on the ground. This is what we could launch into space at least at the end of It is also in low-earth orbit. It's in an orbit that is only 600

4 kilometers up. And those of you who know the distance - the thickness of the atmosphere is about 100 kilometers. You can see that's just above Earth's atmosphere. The major feature of Hubble that is it gets above Earth's atmosphere and avoids the distortion, the twinkle, twinkle little star that we always talk about, that's bad for astronomers, and so Hubble getting above the atmosphere doesn't have any twinkle, twinkle little star. In low-earth orbit it orbits every 97 minutes. And the science program is run here at the Space Telescope Science Institute here in Baltimore, Maryland. Okay, the next great observatory - whoops, wrong button. Here, there we go - on Slide 7 in July 1999 the Chandra X-Ray Observatory was launched. And as its name suggests it does x- ray observations. And you can see that it's a very long tube, tubular shape as in the image on the upper right. And the reason for that is because x-rays don't use a standard mirror; they use what are called grazing incidence mirrors. X-rays don't bounce off a normal mirror, they'd actually go straight through it so you actually have to bounce them on very, very, very shallow angles. And so in the lower right hand you see the four cylindrical mirrors and a sort of depiction, those little orange things are supposed to be x-rays coming in and using grazing incidence to slightly bounce off of the cylindrical mirrors that then focus them down at the end of the - at the detectors at the end of the observatory. So that's why it's a very long thin telescope for this, because it has to focus these x-rays which are very difficult to focus. And it - the x-ray observations are in, you know,.17 to 17 nanometers, very, very, very short wavelengths which mean they're very high energy. They are x-rays of course. Now Chandra is in a very elongated orbit, an elliptical orbit that takes it from 10,000 kilometers above Earth's surface out to 140,000 kilometers. Remember Hubble is only at 600

5 kilometers so it's much, much higher than Hubble even at its lowest point. And again 140,000 kilometers takes it more than halfway out to the distance of the moon. That takes Chandra away from Earth and allows it to do its observations unfettered by any problems with Earth being nearby. But that means it has a much longer orbit. It takes 64 hours and 18 minutes, almost almost 3 days for Chandra to make one orbit through its orbit. And it is run out of the Center for Astrophysics up in Boston, Massachusetts. I think that's everything I needed to say about that one. And then the next, on Slide 8 is the Spitzer Space Telescope. And Spitzer was launched in August of It has a mirror like Hubble but it's smaller, it's a.85 meter mirror so what's that, about 30 inches across. All right so and it observes in the infrared; it's designed to work in the infrared. Hubble goes only a little bit into the infrared, Spitzer does the infrared really, really well. At microns where, you know, one micron is 1000 nanometers. Okay? Now in May of 2009 Spitzer went into what we call the Warm Mission. Because infrared radiation is what you sort of think of as heat radiation Spitzer needs to be cooled to very low temperatures in order to really observe the infrared at the incredible detail that it wants to. It ran out of its liquid helium coolant in May and it transitioned to what we call the Warm Mission. Basically the scientists know how to use this telescope really, really well, they understand it. And even without the coolant if it just is passively cooled by space, which still gets you down to some pretty cold temperatures, just not as cold as they really want, you can still do an awful lot of science and so Spitzer will be continuing on its Warm Mission for the next several years.

6 It is in a really interesting orbit, called an Earth-trailing orbit. Basically it was launched away from Earth and it's basically in a very similar orbit to Earth's orbit around the sun but it's slowly getting further and further away from Earth in the orbit by about 1/10 of an astronomical unit per year. And for the librarians out there an astronomical unit is the distance between Earth and the sun. So if it's been since 2003 and it's six years it should be about 6/10 of an AU, and an AU is 150 million kilometers and so that - it's about 90 million kilometers away from Earth now. See I can do the math in my head. So it's slowly getting further and further away from Earth in its Earth- trailing orbit. That helps of course get it away from Earth and the heat of Earth and helps get it past - better passively cooled out in the solar system. And this is run by the Spitzer Science Center in Pasadena, California. All right, those are the three Great Observatories. And they cover several bands of the electromagnetic spectrum. On Slide 9 you see a graphical depiction of the electromagnetic spectrum going from the very short wavelengths on the left to the long wavelengths on the right. Short wavelengths have higher energy, the gamma rays and x-rays and ultraviolet. In the center you see the incredibly small band that is visible; visible is such a tiny band of the electromagnetic spectrum. And then going on to the longer wavelengths the infrared, the microwave and the radio. Down bottom you have a graphical depiction of objects that are the approximate size of the wavelengths of this various light. On Slide Number 10 is a similar diagram of it but I included this to show you that sometimes it's plotted in the reverse order going from large wavelengths down to small wavelengths. And you should always make sure that you recognize which way it's being plotted.

7 This - both of those diagrams came out of our department here at Space Telescope and we've plotted them backwards and forwards. You have to get used to that in how you're talking about radiation. And in particular on Slide 11 this diagram that I pulled off of the Internet also goes from long down to short, from radio waves down to gamma rays. And what the plot on Slide 11 shows you is the penetration of these wavelengths through Earth's atmosphere. Radio waves and visible light are the major wavelength bands that get to the surface of Earth. We can do some infrared observations from mountain tops but a lot of the other wavelengths that we want to observe you need to be in space or balloon-borne; we need to get up as high above the atmosphere because the atmosphere absorbs a lot of this. So this is the major reasons for having space telescopes, to see these wavelengths observations that you could not possibly do from the ground. And on Slide Number 12 you see NASA's - this is a bit out of date because there are more telescopes than this but this is a relatively complete compendium of various satellites that we have up there doing astronomical observations with Spitzer, Hubble, Chandra and the Gamma Ray Observatory, the other - the fourth Great Observatory, the Compton Gamma Ray Observatory, which is no longer operational, listed as well. So you can see with the four Great Observatories we cover the major wavelength bands across the spectrum, and with the complete portfolio of NASA's satellites we have an incredible number of telescopes that have been operational and are up there to observe the universe. All right so that is the basic introduction into the telescopes and the wavelength regions that they're doing. On Slide 13 I'm going to start talking about the specific observation that we have going here, the galactic center region. So Slide 14 is sort of like that Axel Mellinger image that we put on Panel B but this actually comes from a piece of software called WorldWide Telescope. It's a free piece of software

8 from Microsoft and it was a very convenient piece of software for doing the zoom I'm about to do. So this image here is about 90 degrees wide. And that dark band you see across the center of the image is the Milky Way. And if you get out to a national park where you can get really dark skies or get out on a mountain top where you can get really dark skies you can see the Milky Way with your eyes and it's this band of light and dark racing across the sky. Now we've oriented it such that the band of the Milky Way is flat here. When you see it in the sky of course it will be at various angles. And you'll also notice that the grid does not match up to it because the grid is based on Earth and the Milky Way is not lined up with the rotational axis of Earth. So that cross on the very center of the image is the Galactic Center. And so I'm going to zoom in to Slide 15, all right. And what you can see is that there's an awful lot of darkness there. Okay there are some bright patches but there's an awful lot of darkness around the Galactic Center. Just below center you see a constellation that to many people looks like a teapot with the spout pointed towards the Galactic Center; that's Sagittarius. And then to the right there's this sort of curling tail, that's the tail of the constellation Scorpius and so that's near the Galactic Center. But we're going to zoom in onto the Galactic Center in a couple stages. And on Slide - I guess it's 16 - I've outlined a 12-degree box, okay. That 12-degree is then zoomed up on the next slide. And again you see an awful lot of dark clouds there. These - and the dark clouds in the plane of our Milky Way Galaxy that are blocking our view, and in the next slide you can see I've outlined a four-degree box. And we're going to zoom into that on the next slide. And again we're just seeing a whole lot of darkness here. And then I outlined a one-degree box on the next slide. And then we zoom into that on the next slide. And now you can see

9 some stars here but there are not that many stars, simply because you only go so far into the Milky Way looking towards the Galactic Center before you hit these dark dense clouds. And you only see the stars on the near side of the clouds. Finally we hit the next slide, and you can see a 0.4-degree box outlined on the slide here. That 0.4-degree box is the outline of the images from the Panel B up on the triple panel. That is the region that we're looking at in the images that you're going to see. And if we move forward to the next slide on Slide 23 here is that Hubble image pulled up large, that 0.4-degree Hubble image. And this is in the infrared. Notice that if we had taken this in visible light we really would not have seen much besides just some stars. That's why we had to go to the infrared in order to see things. And you get even better on Slide 24 when you see Spitzer which really does the infrared well. And the longer wavelengths of the infrared are able to penetrate through the dust and see to the Galactic Center. And also on Slide 25 you see the Chandra image and the x-rays are really, really powerful and you got incredible energy coming from the Galactic Center and Chandra is able to see it there. So that just shows you what a small region of the sky we're looking and how dark that region of the sky really is in visible light so but we have to use these infrared and x-ray bands in order to study it with NASA's Great Observatories. That is the end of my introduction here. So let me pause right here and ask if there are any questions from the folks on the telecon about that part of the introduction. Phil Sakimoto: Hey Frank? It's Phil Sakimoto at Notre Dame. I got two questions to ask you, one is you've probably done the math for that smallest box there; can you translate the degrees into parsecs or light years or something?

10 And I'll ask the second question: if you're zooming down in the bottom of all the images there was a piece to the mosaic that came from a different telescope than the others; do you know which two images were in that zoom? Frank Summers: Phil, Microsoft's WorldWide Telescope uses a bunch of different mosaics in what they're doing there. What they're really doing here is taking the digital sky survey and it's not uniformly smoothed across the boundaries between them. Phil Sotimoto: Oh okay. Frank Summers: So that's why you end up with things that have very hard edges in it. Phil Sotimoto: Okay. Frank Summers: Just - WorldWide Telescope didn't - they have a smooth version of it that does it a little bit better but I didn't like it because it actually fuzzes out things a little bit. Phil Sotimoto: Okay good. Frank Summers: And I have not calculated - as Susan, I know, knows the width of that in parsecs at the 26,000 light year distance of the Galactic Center so I'll leave that for her talk, she'll tell you that. Man: And if I could ask another question related to the size of that image and the width I'm sort of used to thinking of this way but is there something like for example that last picture, that.4 of a degree just to give sort of a visual idea of what that is, I'm used to hearing like half a degree is like half the width of your thumb at the, you know, at arm's length and so forth when you're talking about the size of the full moon. Would you like - is there something we could sort of give as a good analogy so that when people look at that image they can understand like this is a chunk of the sky approximately as large as say like a dime held at arm's length or something like that?

11 Frank Summers: Well I don't do the dime at arm's length thing but the full moon is 30 arc minutes so this is slightly smaller - the width of this is slightly smaller than the full moon. Man: Okay. Frank Summers: So this is 4/10 of a degree and the full moon is half a degree. Man: Okay. Frank Summers: So considering the size of the full moon in the sky a little bit thinner than - a little bit smaller than that. Woman: It's about the size of holding a pea at arm's length. Frank Summers: There you go, I knew somebody would have it. Man: There we go. A good-sized pea. Frank Summers: A good-sized pea, yeah. Man: But I think if we're going to be translating this to like - telling this to people, you know, the chunk of sky we're looking at, you know, that's a nice analogy for us. Frank Summers: Great. Man: Yeah. Frank Summers: Any other question on the intro? Deb: Yes I have one question. This is Deb from Indianapolis, the Pike Planetarium. Is there a way to say what portion of the Milky Way we're seeing?

12 Frank Summers: You are looking at the very center of the Milky Way as defined by the black hole at the center of the Milky Way which we'll talk about in a few minutes. But it's in this constellation Sagittarius, okay? Woman: Can I (unintelligible) a little bit. I often say it's the - the constellation Sagittarius is shaped like a teapot and the center of the Milky Way is approximately where the tea pouring out of that teapot would be. So if that helps your visitors visualize it. I like to think of it as the steam coming out because to me it looks like steam. Woman: Yeah, that's a good one too. I like that better actually. Frank Summers: Okay great. Other questions? All right let's move forward to Slide Number 26. And the results - the scientific ideas from the Spitzer Space Telescope with Dr. Susan... Stolovy. Frank Summers:...Stolovy, there we go. And Susan if you would make sure that you say next slide every time you change your slides. I will. In fact I noticed that some of my slides seem to cover up the numbers... Frank Summers: That's all right....in the corner but you guys could figure it out. So thank you very much for - me to give this presentation. The Galactic Center is a region that is very dear to my heart; I've been studying it for quite along time. And I am always excited to be able to use a new toy to look at it with. So Hubble - I worked on the Hubble most recently and also the Spitzer images. And I'm going to start with the Spitzer telescope data. So if you start with - I guess the next slide is Slide 27.

13 And that is the image that you saw before. And that is the image from the Spitzer Space Telescope. You're going to see in my next few slides that actually the Spitzer image is - we have four different cameras that took pictures that range in wavelength between 3.6 and 8 microns. And the image you're looking at right now here is actually a combination of the shortest wavelength camera, the 3.6 and the 8 micron. So if you see the centers of the stars kind of sharper than the - the bright stars have kind of a sharp core and a little bit fuzzier core because it's two different wavelengths put together. And the longer wavelengths give you a little bit more spread out image called the diffraction limit of the telescope. So what you see in this image is of course lots of stars. And you also see very spectacular filamentary structures in diffuse dust emissions. So you actually are seeing glowing dust here. And I m going to tell you a little bit later about the nature of that dust that you actually see. We're seeing through the dust in the galaxy to get through to the center. And this dust is actually warm dust that's being heated by stars and it's glowing. The other - I wanted to point out a couple other things in this image, your eye clearly can see there's two very bright spots in the lower right and in the lower left. And the lower right is actually the very, very center of our galaxy; it's called Sagittarius A. In fact that is called Sagittarius A West. But - and then the very center of that is a black hole that I'm sure Peter will tell you more about from the Chandra data. Although it's pretty much the brightest part of the whole image the black hole itself is not bright in the infrared - in fact it's extremely dim; we've been looking for it for years. But what you see here is actually just a bunch of stars and gas that are crowded together there. And there's a cluster of stars there that are massive and young.

14 Same thing with the lower left image, this is a cluster of stars, it's called the Quintuplet Cluster because there's five extremely bright infrared stars but there's also another cluster of hot stars that are not so bright in the infrared. There's one cluster that you can't see very well in this image but it's called the Arch's Cluster, it's further up - higher up. And that also has a cluster of young stars but they're not dusty so you don't see them very well in the infrared which shows a lot of dust emissions. So let's go to the next slide. Frank Summers: Susan, could I pause you for one second? Sure. Frank Summers: You pointed out something that I forgot to mention was that the Galactic Center is not centered in the image. Yes. Frank Summers: As you go back to that - if you look back later on to that 0.4-degree thing you'll notice that that little cross is not in the center of the image. The Galactic Center is in the lower right as Susan has just pointed out. Okay now next slide. Right and the reason why that is is that we're trying to align it with the Hubble's data which actually did extend to the other side a little bit but it's not as spectacular and they're not as bright. Actually a point I wanted to make that there's a lot more star formation happening on the left side on this image of the Galactic Center than there is on the right. And so it's asymmetric, there's a lot more raw material to make stars on that side. Okay so now on the next slide, Slide 28. Why observe the Galactic Center with Spitzer? Well the quickest answer, and I think you already know this, is because you can. Obviously we'd

15 want to study the center of our galaxy; it's the closest galaxy to us - our own galaxy - and we're interested in what happens in the center. The next closest galaxy like ours is the Andromeda Galaxy and that's 100 times farther away. So we get a picture that's 100 times sharper when we look at our own galaxy versus the next closest large spiral. So yes we can observe the Galactic Center in infrared wavelengths. It is completely invisible in the wavelengths that the human eye can see. And I like to think of wavelengths in terms of microns so it's a millionth of a meter is a micron and your eye sees from about.4 microns which is violet to.7 microns which is red. So the Spitzer Space Telescope images are all three microns or longer so it's quite a bit longer than the human eye can see. And so that's why we want to look at it with Spitzer and Spitzer can actually see through the dust. There's still a little bit of absorption of dust at Spitzer wavelength, but about 25% of the light gets through at the Spitzer wavelengths so we still see plenty. And this is an artist's schematic of the Milky Way. Of course we're in the Milky Way so we couldn't actually ever get a picture looking like this. But if we were in an imaginary spaceship flying outside the Milky Way and looking at it face-on we think this is what it looks like. It's a big spiral and it has a very large bar in the middle. And actually we're learning about the structure of the galaxy from Spitzer data; not just of the Galactic Center but mapping out the whole plane. So one thing we might do later is give you some links to the GLIMPSE survey images that basically show not just the Galactic Center but on either side of the Galactic Center. And we're actually going to complete that and go all the way around the galaxy with Spitzer, it's happening right now - actually that data is being taken now.

16 So we're understanding the structure of our galaxy from Spitzer data because we can actually see through the dust. And if you can see the center of - there's an arrow that I've drawn between the sun and the center so that's our view at the sun, and then we're looking towards the center. And you could see there are intervening spiral arms and the arms especially have (not stars) but they have a lot of dust because that's where stars are formed in the - a lot of star formation in the spiral arms happening now so that's what we have to contend with. Next slide, Number 29. So I mentioned there are four eye IRAC wavelengths that we are observing here. IRAC is the infrared array camera that's the shortest wavelength instrument on Spitzer. There's actually longer - even longer infrared cameras as well as a spectrograph but I won't be talking about that in this talk. So you can see the 3.6 micron image and the 4.5 micron image look almost exactly the same. And it's true. And they show a lot of stars right in the center. It also shows a lot of dark dust and the darker the dust the closer it is to you so you get a little clue about the three dimensionality of this image; what's where and so they look almost the same. Five point eight microns we see a lot more fuzzy diffuse nebulosity; that's this glowing dust. And at 8 microns you see even more of that and less starlight, less little points of light. So those stars that we see - there are many, many kinds of stars in our galaxy, many like our sun. But it turns out that the Spitzer Space Telescope is mostly sensitive to a kind of star called a red giant. And the sun will become a red giant in about five billion years but there are lots of red giants in the galaxy and that's what we're most sensitive to so that's basically what we see. And we actually see them all the way to the center of the galaxy and close-by ones and far away ones. All right Slide Number 30. David: I'm sorry Susan?

17 Yes. David: This is David from the Discovery Museum in Bridgeport. In the infrared IRAC camera images is - the Galactic Center is in the center of each image is that correct? That is true, yes. David: Okay. Good question. And in fact I wanted to mention the field of view here is quite a bit larger than the other images that we'll see from Hubble and Chandra. So this is actually - a cross this image is about two degrees. Yeah, I think it's 1.9 degrees across and 1.4 up and down. And then, yeah, and it's centered right on the center of the galaxy. Yeah. Okay next one. Now I've tilted the image 90 degrees so that the plane of the galaxy runs up and down. And I wanted to show you the power of going to long-area infrared wavelengths. Even at the left hand image, at 1.25 microns, that's still longer wavelength than the eye can see and that's still considered to be near infrared. You'd have to have a lot of imagination to be able to say oh that's the galactic center. You really can't see it - barely see a little bit of tiny little emission there but it doesn't look very spectacular. You mostly are seeing just the foreground stars and also dark dust. Two point two microns, that is really starting to pop out there. You can start to see through. And then the 4.5 microns and the 8.0 microns are from Spitzer. The 1.25 and the 2.2 are actually from a ground-based telescope called 2MASS Survey Telescope. But it actually matches the Spitzer resolution or sharpness pretty well so that's why I put it in this slide. Next slide, 31 is - I'm going to go through this fairly quickly. There's just some details about the actual Spitzer observations and what you're actually seeing in it.

18 The field of view, there it is for you. It's 890 x 640 light years. That's assuming the distance at the Galactic Center is about 26,000 light years and that is a good estimate of distance. But we're also seeing a lot of things that are closer to us in that image. The area in the sky covered is 1.9 by 1.4 degrees. And if you figure out how much area that is it's about the amount of area that 14 full moons would cover. That's a pretty big chunk of sky. It was observed with the four wavelengths that I mentioned. And I already talked about how the two shorter wavelengths mostly shows stars and the long wavelengths shows some stars but also shows glowing dust. Now what is this dust? There's all kinds of dust in the plane of our galaxy that's sort of left over from star formation and also are the ingredients for new star formations. And it's made of particles - the same kind of materials that our bodies are made of, carbon, oxygen but also iron and there's many other elements but silicate is also an important one. It's the kind of stuff that you find in your bodies and it's all started from stars originally, the stars make heavier elements than hydrogen and helium in their centers. But we see glowing in Spitzer image is actually a very specific kind of dust that happens to be extremely bright at those wavelengths, in particular 8 microns. And that stuff is - think of them as giant molecules or very small dust particles. They're called polycyclic aromatic hydrocarbons and they're kind of soot-like particles and they actually exist here on Earth in the pollution on Earth. So it's everywhere. But it's kind of nice for astronomers because it lights up wherever there's star formations. So they're very useful and that's why we tuned our cameras to be sensitive to those wavelengths. And another nice thing to say about this IRAC data is it's very efficient. You cover a large field of view in just seconds. We took - each exposure here was actually 1.2 seconds. We took a few exposures for each position and it was five arc minutes by five arc minutes a side. And the whole survey only took 16 hours to do of real time on the telescope.

19 And actually four of those hours were spent on the very center of the galaxy, the Galactic Center and the Quintuplet Cluster and a few other places that would saturate our detectors so that it's too bright to see anything. And those ones we did even shorter exposures using a little tiny part of the array, it's called sub-array mode. That's a little detail but it's actually an important one because when I originally wrote the proposal to do this a lot of people said ah, you can't see the Galactic Center with Spitzer, it's going to saturate, it's too bright. Well it turns out it wasn't true. It was only too bright in a few places that we knew about ahead of time and so that's why I structured this proposal to be next to the short exposures and super short exposures. Okay next image, it's an 8-micron image of the Galactic Center. And I actually - there is a higher resolution version of that that doesn't look so great in this. But you can see a little - you can see obviously the plane of the galaxies glowing in dust. There's a lot of dark dust right - especially on the left side of the galaxy. Those objects are really at the Galactic Center. If you go off the plane especially to the lower left and upper left you see some really spectacular clouds. Those are star forming regions that are closer to us. They're at intervening spiral arms. And then you also see some sort of long stringy things that are going away from the center on the upper right and lower right and also kind of right in the middle. And we think those are outflows that might have something to do with the very center black hole so we don't really know for sure. Next slide, Number 33. This is a close-up the top part is just the plane of the galaxy cropped a little bit and then I've shown four close up areas which I just thought looked really interesting. Number one, the lower left panel, that's actually we think possibly an intervening spiral arm a little closer to us. And actually that's an x-ray source too, Peter.

20 And there looks like two little twin star forming regions. And there's also a lot of dust right near there, long stringy filaments of dust that we are imaging for the first time at very high resolutions. The second panel is a really fascinating area that looks even more spectacular in the Hubble image. The Quintuplet Cluster and also the thinner-like structures to the left of them called the - it was known before in the radio - as the Sickle because it made kind of an arc-like figure but now at high resolution you see that there's lots of little fingers. And we think it's actually being - material that's being blasted by the light and also particles from a very hot cluster of stars in the Quintuplet Cluster. And have you ever seen the image of the Eagle Nebula called the Pillars of Creation from Hubble, it's a very famous image, that's an object that's about four times close to us. And we think it's the same kinds of thing happening around the Galactic Center. And in the whole image that we surveyed this is the only place that has those fingers so it's kind of a unique thing to look at in the Galactic Center and we're very interested in it. And it's possible that new stars will be born in the future in those fingers, new baby stars but we haven't proven that. Number 3 is another interesting region with lots of young stars forming in those bright little bit fuzzy areas. And then there's long strings - filamentary strings coming out of that as well. And in Panel Number 4 that's the very center of the galaxy. And I mentioned before that there's a black hole in there and we know the mass of it from other observations because we can see stars moving around it in real time. We know that it has a mass of about 4 million times the mass of our sun. So it sounds really huge; we do call it the supermassive black hole but actually compared to the centers of some other galaxies like ours it's not very heavy. There's some that are like 1000 times more massive. So we have a big black hole but it's not as massive as in other galaxies. And also right now it's not eating very much although it's

21 nibbling material, which is why it's not so bright in the infrared. It would be really bright in the infrared if it was - if material was sucking in. And it's true that a black hole really is black at all wavelengths but the material falling into it could get heated up to very hot temperatures and that would glow so that's why a black hole might appear to be bright. And so there is a lot of gas and dust swirling around and that's what you see in the Spitzer images. Next slide, Number 34, this is a little complicated to look at but I just wanted to show you that we're looking in all wavelengths to try to understand the Galactic Center. And another wavelength that we look in is the radio. In fact radio wavelength is very important for the Galactic Center studies because that's the first wavelength where we saw an actual bright point source right at the center of the galaxy in the black hole. You can't see it in this image because it would be a tiny dot. But a lot of the names that we use like Sagittarius A, Sagittarius B, Sagittarius C, those are all regions that were discovered radio emitting images and radio wavelengths. So what I have in this image here is everything that's red is taken at a radio wavelength of 20 centimeters with a very large array which is in New Mexico. And it shows some really oddlooking things. There's a big bright red blob in the middle which is not surprising because there's a lot of hot ionized gas. There's also some silver remnants that looks like a shell or a circle or bubble, it's probably a supernova remnant left over from the explosion of a massive star. And then there are these very strange filaments that go perpendicular to the plane. And we still don't quite understand what they are but we think it has something to do with the strong magnetic field there. So, I mean, just - everything that's sort of yellow here is seen in both green and red so that's - and blue - I guess the white is what you see in all the wavelengths. The ionized gas and the dust is often seen in the same area. So the green which is the Spitzer 8-micron is the dust glowing and the red is hot ionized gas.

22 Next picture. Just a summary of some of the results that, you know, the best large view of the Galactic Center over a very large area. We have higher resolution images of just the central few light years but not of the whole giant mass like we did. And we see a lot of interesting structures. Over 1 million stars were detected but an interesting point to make is that we know there's a lot more stars than that in that image, we just can't quite separate them because they're so crowded together. And there we do better with Hubble because Hubble has better resolution. We'd actually see a lot more stars with Hubble in a smaller area. So there's dark clouds, there's a lot of star formation. And another little piece of science we followed up on this data based on the infrared colors actually that we found some new baby stars forming in the Galactic Center based on their spectra. So the last couple slides here, the infrared view from 1968 was a line plot with a single detector. It moved across the sky in the direction of the Galactic Center and that's courtesy of Eric Becklin. And that used to be our view of the Galactic Center, just a bump in that red line plot there. And now our view, the last slide, is - this is a composite of four colors from Spitzer. So you have a lot of different versions of this Spitzer image. You have the two-color one which is part of the IYA press release and this is a four-color one and they're color coded. Frank Summers: All right, let's pause here and ask if you - ask the telecon participants if they have questions about the Spitzer Space Telescope science. Dave Hofstetter: Yeah this is Dave Hofstetter in Lafayette. I just want to clarify with those four IRAC images they were 1.9 degrees wide and the image that we will be receiving is 0.4 degrees wide so they're significantly larger than the image we're receiving? That's correct. Dave Hofstetter: Okay thank you.

23 Frank Summers: Other questions? Woman: I'd like to ask about Slide Number 34. Besides everything that's going on with the green and yellow in the center there's a lot of kind of shadowy red all around it. Yes the question was do we have any idea what that is. Yeah, to be honest the radio data aren't very - they don't have what we call high signal to noise. It's noisy. So there's actually - I wouldn't believe most of the stuff around the edges. Woman: Okay....it's hard to explain but, yeah, basically it took a lot of pointings of the VLA to make that mosaic. And there's a bright image in the field that can kind of throw off other parts so it's hard to make a mosaic. So mostly just look in the point of the galaxy, that's believable. Woman: Okay thank you. Thank you. Woman: Susan, I have a silly question? Sure. Woman: I have heard that the dust of the galaxy tastes like raspberries. Well that's interesting. Woman: Yeah. No I heard almonds.

24 Woman: Almonds. Almonds, okay. I had just wondered. It looks tasty besides being so amazingly beautiful. Is that one of the pleasures of your job is finding, I mean, this amazing beauty? Yes absolutely. I mean that's - actually to be honest one of the motivations for writing this proposal was just let's get a really pretty picture out of it. ((Crosstalk))...but we knew it was going to be big payoff. So sure that is one of the joys absolutely. And I have no comment on the taste because... Woman: You have never tasted galaxies. Frank Summers: Okay I need to break things up because we only have another what 12, 13 minutes and we've got Hubble and Chandra to get through. Okay. Frank Summers: Okay so moving to slide 38 the Hubble Space Telescope. Again, Dr. Susan Stolovy. Right. And this one will go faster because I already talked about a lot of stuff. So this is the image from Hubble, Slide 39. And what's different here is first of all it's a much sharper image, ten times better spatial resolution. But also you're not seeing blowing dust, you're actually seeing hot hydrogen gas - they often exist in the same places where there's star formation. But it's not exactly the same physics that we're seeing as in the Spitzer image. And that's also a lot of stars. And also most of the stars we see are red giants, but there's this population of very interesting stars that are not red giants that are very massive stars with big winds, and I'll talk about them a little more with the data set.

25 So Slide 40, I mentioned we're observing ionized hydrogen gas. Hydrogen is the most abundant element in the universe. And there's the same thing for the actual wavelength we're looking at it's the Paschen Alpha - I don't think you need to really use that terminology but if you ever hear it I thought I would explain it which I will say a little more later on in my survey why it's called it that. And this is using NICMOS, the Near Infrared Camera and Multi-Object Spectrometer. And it's just the camera part of that that we're using here. Although there's still much absorption of light at 1.9 microns from the Galactic Center by the dust in the galaxy, enough gets through. We have to take pretty long exposures to get this but enough gets through in the wavelengths that we're looking that we can make a nice snap. About 2% or 3% of the light for the center of the galaxy gets through at this wavelength. And again this is a sharper image and it can help us understand how massive stars interact with their environment. Here's some survey details. I think I'll probably skip most of this since you guys can read it. Frank Summers: Slide 41. What was that? Frank Summers: Just wanted to remind them it's Slide 41. Yes, Slide 41. So the field of view it's about half this area covered by a full moon. And Paschen Alpha is named after German physicist who discovered it. It was a line in the infrared but he didn't discover it in space because you can't see this line from the ground, you have to go - it's absorbed by the Earth's atmosphere and that's why you need to go to space. And this took a long time to do with Hubble, unlike the Spitzer which was very quick to do, it was not efficient with Hubble but still it s pretty ambitious - an ambitious project that paid off because we got - we're going to get a lot of science out of it and it's a spectacular image.

26 So Number 42, making these images is a little tricky. It's not - it's harder than with the Spitzer ones because you actually have to subtract two images to get the glowing hydrogen gas picture to isolate light from the glowing hydrogen gas. So the one on the left is the way it looks coming out of the telescope in the 1.87 micron called F187N filter. The one in the middle is after subtracting another filter with a slightly longer wavelength, 1.9 microns. And then the third one is just a different version of that with all of this little - star points subtracted from it if you're interested in the diffuse gas. Next slide, 43, on the top is the big map and the 1.87 micron image. And we detect in this image 600,000 stars. So like in this image in the Spitzer we don't detect as many because they're all mushed together. But now we can actually detect individual stars really well. And notice there's some spectacular dark clouds in here. And the bottom one shows the Paschen Alpha image, so if you're just seeing the glowing gas there and also seeing some stars that are glowing in the Paschen Alpha because they have wings coming from them. Next one, some close ups. This is the best image of the very center of the galaxy that you'll see in this talk, Panel A. And you should see there's this sort of spiral shaped gas cloud swirling around the Galactic Center. We don't actually think that they're falling in, they're mostly just orbiting around but little bits are falling into the two black holes. And Panel B... Woman: Susan, can I ask a question? Sure. Woman: I'll be fast. Yes.

27 Woman:...Observatory. When were these photos taken from the Hubble? They were taken about a year ago. I can look up exactly when but they're recent. Woman: And which camera? It's called NICMOS. Woman: Okay. That's actually on my previous slide so... Woman: Thank you. You see something that looks like fingers that are being sort of sculpted by winds from massive stars in the central region of that image. And then in Panel C you see some really amazing filamentary structures, it's very long and skinny. We think that they're aligned with the magnetic field structure in the Galactic Center. Next image. These are some close-ups of some objects that are very interesting that are in our Paschen Alpha image. And they show different kinds of compact - they're not even spread out, these are compact, small little blobs of ionized gas. And we think that they show different stages of stellar evolution. The top ones might be newly forming stars. The middle ones we think a lot of them are more evolved stars that have made a nebula around them. And the bottom ones are probably also - a little bit larger regions where there's many stars forming inside them but we're still studying these. And I think I'll stop there. You can read the last slide on Page 46 and take any other - oh I will mention one other thing, and that's one of my bullets here, that we have found these massive stars - probably more than 100 of them. And some of them are in the three clusters

28 that I mentioned before, the Central Cluster, the Quintuplet Cluster and the Arches Cluster, those were known before. But quite a lot of them are spread around in between them. So that's very interesting and it could mean that they were born in the clusters and they were ejected, or it could mean they were born by themselves somewhere else, or maybe they were born in a cluster somewhere else and have since broken up by the gravitational field in the Galactic Center. So that's all I want to say about this. Thank you very much. Frank Summers: Okay so we'll pause here and ask if there are questions about the Hubble portion of the talk. I would make comment that what you've seen so far you've seen that in visible light we see a lot of the cold dust. In infrared light we see the warm dust at least the Spitzer infrared - the long wavelength infrared. And in the Hubble infrared you're looking for the hot gas that is excited by light from young massive stars. So you're going from cold, warm and hot with the three different wavelengths that we looked at so far. Right. Frank Summers: Any other questions about Hubble? Man: Could I ask one quick question about Slide 45 again? Sure. Man: The top row are early stars... We don't know for sure but we see that they have dark dust lanes in them that are probably - it's probably stars that are forming and they would be massive. But we don't know, it could be they can be completely different objects. Like the one on the left which looks like Saturn kind of, upper left, that could be a planetary nebula or something else, we're not sure.

29 So this is the fun part, the discovery part. We need to follow up with taking spectra of these objects to try to figure out what they are. Man: Thank you. Frank Summers: All right if we move forward to Slide 47 the Chandra X-Ray Observatory presentation will be done by Dr. Peter Edmonds. Take it away Peter. Peter Edmonds: All right thanks Frank and thanks Susan, those were beautiful images. So you've heard about how you can get a good view of the center of the galaxy in infrared. And in x-rays you're also able to probe through the murk, through the gas and dust in the plane of the galaxy. And if you go to Slide Number 48 you see an x-ray view of the Galactic Center. And this is a color image - the top image is a color image released by us just a couple of weeks ago for our 10th anniversary meeting that we had here in Boston. So we had our 10th anniversary - 10th birthday. And the field of view of the IYA image is shown in the white box. So this is a field of view that's bigger just like the Spitzer that's bigger than the IYA image. Just a few technical details about this image, it's almost two degrees wide. And it's about half a degree high. And that amounts to about 900 light years by about 260 light years. And it was based on a lot more observing time the Spitzer observations, it was 26 days of observing with 88 different pointings so it's a mosaic of different points of Chandra so that's almost a month of observing was put together. And, you know, there were more observations done of the region right around the center of the galaxy and the other parts of the Galactic Center. So one obvious question is what do the colors mean in this x-ray image, because we can't see in x-rays. I mean Superman could see in x-rays but we can't.