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You’re familiar with the Hubble Space Telescope, of course, but it’s just one of NASA’s Great Observatories. After Hubble came three more incredible observatories, each greater than the last. Together, they would fill in almost the entire electromagnetic spectrum.
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NASA’s Great Observatories (NASA)
Fermi Gamma-Ray Telescope (NASA)
Enrico Fermi (Wikipedia)
NASA Celebrates 25 Years of Breakthrough Gamma-ray Science (NASA)
Spitzer Space Telescope (Caltech)
Chandra X-ray Observatory (Harvard University)
Introduction to the Electromagnetic Spectrum (NASA)
Adaptive Optics (ESO)
How Fixing the Hubble Spacecraft Works (How Stuff Works)
GRB 990123 (Wikipedia)
Brighter than an Exploding Star, It’s a Hypernova! (NASA)
G344.7-0.1: When a Stable Star Explodes (CXO)
The Neil Gehrels Swift Observatory (NASA)
Habitable Exoplanet Observatory (HabEx) (NASA JPL)
Spitzer Captures Cosmic Mountains of Creation (NASA)
Spitzer View of the Center of the Milky Way (Caltech)
What Is The Great Attractor? (Universe Today)
Farewell Compton (NASA)
Kepler and K2 (NASA)
Voyager (NASA JPL)
Transcriptions provided by GMR Transcription Services
Fraser: Astronomy Cast. Episode 616: The Great Observatories. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos where we help you understand not only what we know but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey, Pamela, how you doing?
Dr. Gay: I’m doing well. I have been streaming for almost 13 hours now. Some of you out there listening to this aren’t watching live. We are recording this episode of Astronomy Cast during the 2021 hangout-a-thon as we work to raise funds to keep all of our programs going. But, we are taking this time to record a very special episode of Astronomy Cast on a topic I can’t believe –
Fraser: A great episode.
Dr. Gay: Yeah. I can’t believe we haven’t done this yet.
Fraser: Well, we’ve done it in pieces.
Dr. Gay: Sort of.
Fraser: Yeah. Yeah. I think we have. But, yeah, to think, 15 years, we haven’t talked about the Great Observatories. Now is their time.
Dr. Gay: Yes.
Fraser: I mean, by your rules, I guess, some of them are still operating. So, I think science has been delivered. So, I think now it’s fair. Now we’re allowed to talk about them, right?
Dr. Gay: Yes. They’ve done more than return first light.
Fraser: That’s true. All right. Well, you’re familiar with the Hubble space telescope of course. But, it’s just one of NASA’s Great Observatories. After Hubble came three more incredible telescopes, each greater than the last. Actually, that’s not true. The first one was the greatest. But together, they would fill in almost the entire electromagnetic spectrum. All right, Pamela, let’s talk about the Great Observatories.
Dr. Gay: Where do we start?
Fraser: So, did they start – did they name them before they launched them?
Dr. Gay: No. No. So –
Fraser: They named them after they launched them?
Dr. Gay: Yeah. So, this is one of the things that those of us who are of a certain generation, I will say, we look at the fact that JWST, which I am just gonna call JWST, we look to the fact that it was named what is now decades before it launched. And, we’re just like, “You cursed it.” You wait to name the telescope until it has first light. I was out at Sonoma State Observatory doing a workshop for GLAST, which is now the Fermi telescope. Right after Fermi’s launch, while I was there, they were getting back first light from the telescope, and they were corresponding with Fermi’s family to be like, “Okay. So, the telescope works. Everything’s good. Are you down with us naming this telescope –”And, it was much more formal and much more dignified.
But, “Are you down with us naming this telescope after Enrico Fermi to celebrate his life and his discoveries?” And, that’s the way I really think it should be.
Fraser: Yeah. Yeah, I a hundred percent agree with you. The original name for James Webb was the Next Generation Space Telescope.
Dr. Gay: Yes.
Fraser: And, a name that I saw on Twitter that I really liked was the Very Cold Space Telescope. So, I think you’re exactly right. Give the telescope a working name that is very utilitarian, and then when it achieves first light, when everything is done and safe and then the spirit of the telescope arises in your mind and then you give it its proper, formal but also naming after a person who’s important.
Dr. Gay: And, my favorite head cannon of space telescopes comes from our producer Ally, who at one point spontaneously said something along the lines of, “The reason JWST is so delayed is it doesn’t even like its name, and it’s waiting for new one before it will deliver the science.”
Fraser: Yeah. There you go. So then, let’s talk about the Great Observatories. So, what are they? We’ll start with that. What are the Great Observatories?
Dr. Gay: So, the Great Observatories are the Hubble Space Telescope, the Compton X-Ray Observatory, the Spitzer Infrared Observatory and of course, the Chandra X-Ray Observatory.
Fraser: And so, why did they call them the Great Observatories? Was it just because they were sort of launched around the same time?
Dr. Gay: No. It was actually a concerted effort to launch a suite of telescopes that would cover pretty much the entirety of the electromagnetic spectrum as we had the technology at the time to do it. We’ve been looking, and by this, I mean generations of astronomers before me because I was not – my parents weren’t even born yet. So, back in the 1940s, folks realized that with space-based technology, we’d be able to get telescopes up above all the atmospheric noise and turbulence that distorts so many astronomical images. And from up there, we’d be able to make out details, find structures we otherwise would never, ever be able to see until we got adaptive optics, which was not yet imagined yet in the 1940s.
From this imagining of the optical telescope in space, it was simply a matter of time before people started thinking, “You know, we can’t see x-rays from Earth. And oh “expletive,” it turns out the universe is producing gamma rays and we didn’t know that.” That was discovered entirely by accident. Infrared blocked by our atmosphere. The only way we can see all these different colors of light and get high-resolution optical images with the technology we had back in the 40s, 70s, 80s was to put the telescopes in space.
Fraser: It’s interesting when you imagine the entire electromagnetic spectrum.
Dr. Gay: We’re leaving out radio. I do have to acknowledge radio exists. We’re doing that one from the ground.
Fraser: Sure. Yeah, yeah. But, I mean, you imagine, you start on the radio end of the spectrum and you’ve got microwaves, those work well with going through the Earth’s atmosphere. And then, you shift into infrared, far infrared and even bits of near infrared, and it’s really hard to go through the Earth’s atmosphere. You’ve got to get very cold. The Earth is hot. It’s tough. Visible light? Sure, that works. Ultraviolet sort of works, but then at the higher end, it’s not gonna work well. And then x-ray doesn’t work and gamma radiation. And so, there were these just giant areas of the entire electromagnetic spectrum that we just couldn’t see.
Dr. Gay: And, the problems the atmosphere that plagued the optical and then simply absorbed away all these admittedly harmful, bad for our health, we don’t really want them on the surface of our planet.
Fraser: Yeah, they can stay in space.
Dr. Gay: They can stay in space. But, as scientists, we’d like to be able to get to them please, and that means orbiting observatories.
Fraser: Yeah. I was talking with an astronomer from the Chandra x-ray Observatory, which we’ll talk about in a little bit. And, he was saying that the vast majority of the sort of interesting parts of the universe are in the radiation of x-rays. All the hot gas that’s in between galaxies, a lot of just large-scale structure of the universe is only emitted in x-rays.
Dr. Gay: The cores of galaxies glow in x-ray
Fraser: Yeah. And without x-rays, you really can’t just understand the structure of the universe. And so, we were blind to it until we had a chance to be able to have it. So, you’ve got these four observatories. What order did they launch in?
Dr. Gay: So here, I have to admit I have to look at my notes. Again, I’ve been streaming for 13 hours. So, the Hubble went up in 1990, Compton went up in ’91, Chandra in ‘99, and Spitzer in 2003. And for the most part, they were all expected to last on the order of 10 years, 15 years. Poor Spitzer launched in 2003 was only slated through 2009 when it ran out of coolant to observe the longest of the infrared colors during its cold operations. But, they found a way to keep Spitzer going until 2020 when it simply drifted too far away in its orbit for easy communications with Earth. These things were tanks except for Compton.
Fraser: Yeah. Yeah. So, I mean, even Compton went for a long time. We’ll go in order of launch. So, I mean, Hubble in 1990 of course, we’re very familiar. It was launched from the space shuttle –
Dr. Gay: Yes. And the original plan was for all of them to launch from space shuttles.
Fraser: Yeah. Yeah. And, three of them did. And then of course, we’re all very familiar, I am assuming, with the big problem after the Hubble launch in 1990.
Dr. Gay: And, that big problem when Hubble launched was – and we talked about this briefly earlier today during the hangout-a-thon, not that that helps those of you listening to the podcast. When they were grounding the mirror for Hubble, they thought that they were using a specially placed focal point to focus the mirror while they ground it. And, it turns out they were actually focusing on a fleck of something they weren’t supposed to be focusing on. And as a result –
Fraser: I never heard that story. I didn’t realize that’s what was going on. So, they were focusing on the wrong spot.
Dr. Gay: Yeah. And so, they ended up with a perfectly ground mirror for the wrong optical system. But, because it was a perfectly ground mirror for a different focal length, they had the ability to fix the Hubble by launching essentially corrective glasses. And so, this correction system that they put up during the servicing mission, well, that was everything we needed to do all sorts of amazing science that studied planetary objects, found moons around Pluto before New Horizons got there, that is allowing us to explore the first galaxies forming in our universe through gravitational lenses. It’s an absolutely amazing, amazing set of science that it’s done through my entire adult life.
Fraser: Yeah. Yeah. It’s so incredible. For the other missions, we’ll talk about when they may or may not have ended. Two are still working; two have ended. But, I mean, just Hubble is the first in and could very well be last out that we are already 32 years into operation with Hubble. It has changed our understanding of the universe in ways that nobody had ever predicted. And yet, it is still going strong. It is oversubscribed every year. Astronomers line up to use Hubble and it is still providing some of our best images.
Dr. Gay: And, one of the weirdest facts about the fact that it’s still up there and working is it’s still up there and working because we still don’t have the JWST. The original plan was both telescopes are going to be run out of the space telescope Institute in Baltimore. And, I remember attending talks in 2007, 2008 there they were talking about with JWST, the budget is such that they can’t operate both telescopes at the same time. So, had JWST launched as planned in the early 2000’s, it was supposed to be up in 2009 when Spitzer was out of its coolant. Had JWST been up during 2009, we wouldn’t have had that final servicing mission that brought that last great suite of instruments that we continue to use today.
Fraser: Yeah. And, there probably will not be, almost certainly will not be another servicing mission unless Starship gets really good really fast.
Dr. Gay: That would be amazing, by the way.
Fraser: And it would just go and gulp up the Hubble and bring it back down to Earth. They can make all the improvements and then send it back up. That would be great. But, I think otherwise, maybe Hubble has another 10 years in it before it will finally wear down and it’s time to deorbit it. So, that’s Hubble, the one we’re most familiar with. Let’s talk about the one that we’re probably least familiar with but went next, which is the Compton Gamma Ray Observatory. So, what was its job?
Dr. Gay: So, its job was to allow us to finally get a really good understanding of this really weird wavelength of light that we hadn’t as a profession initially thought was going to be scientifically interesting. This is the gamma ray. It’s the shortest wavelength of light, emitted by the hottest and most energetic things in the universe. And, one of my favorite moments with Compton was it was out there observing gamma-ray burst 990123. Now, up until this point, we knew that there were short gamma-ray bursts that were just bleeps in the night, fractions of a second. We knew that there were longer ones that were minutes, tens of minutes in a few cases.
There was a continuum with a big old dip in between. But, we had no idea what gamma-ray bursts were. We didn’t actually know if they were actually in our galaxy or beyond. And, it was with that GRB 990123 that we finally saw an optical counterpart for the first time. So, Compton was there observing the gamma ray. It’s going, “Hey, folks, over here. Look over here.” And, we were able to get enough telescopes in the correct part of the sky to figure out what new thing was shining in the night. And, this started us down the path of figuring out that gamma-ray bursts are associated with certain kinds of exploding stars that we now refer to as hypernovae.
Fraser: Right. And, because these things explode so quickly, it was really tricky to bring Compton to bear on the target in time. And in fact, that idea of quickly responding, and other gamma ray observatories came afterwards that were highly specialized for being able to find these objects within a minute of when they exploded. But, it’s quite a feat to be able to make these observations that early and provide those details. And before that, people had theories, but they really had no idea of what was causing these gamma-ray bursts. It was a ludicrous amount of energy was being blasted, almost like a laser beam across the universe, so much energy that you could be on the other side of the Milky Way and be hit by a gamma-ray burst and have your atmosphere blasted off of your planet.
So, the fact that they were able to make these kinds of discoveries, and that was just one. I mean, there were many, many more incredible accomplishments that the Comp did, but I think you’re right. That was one of the big ones. Let’s talk about Chandra because Chandra went next.
Dr. Gay: Chandra, there’s no end to what this telescope is able to really accomplish. And, the amazing thing about Chandra is it’s not in the orbit it was originally intended to be in. They got everything working perfectly. It is on an elliptical orbit that carries it out beyond the Earth’s Van Allen radiation belts, brings it back down, and orbit after orbit, it’s out there looking at the hot gas that fills the center of galaxy clusters. It’s out there identifying the crackles of high energy radiation around pulsars in the vicinity of white dwarfs that are parts of systems where the white dwarfs are cannibalizing material off of their sister and brother stars. There is all of this dynamic, often destructive, physics out there that we see through these x-rays.
Fraser: Yeah. Like, the regions around supermassive black holes.
Dr. Gay: Yes.
Fraser: As you say, the afterglow of exploded stars, the high energy interactions between solar flares and their planets. It’s kind of amazing. And again, as I said, in the minds of x-ray astronomers, it’s the way the universe really looks. We’re spoiled. We see the visible light, but that’s not how the universe truly looks. If we could see the whole spectrum, it would be the x-rays that are just blasting.
Dr. Gay: And, this brings us to one of the things that Chandra does in partnership with the other observatories, but, they’re the ones out there putting everything together, is month after month, year after year, going on decade after decade, Chandra has been doing these deep observations in the x-ray of all sorts of different phenomena. We have seen Chandra mosaics of supernovae, of galaxies and they’ll put out press releases that bring together Hubble images that bring together Spitzer images, and their own Chandra images to show us this false-to-our-eyes color image of what the universe would look like were we able to enjoy the entirety of the electromagnetic spectrum.
And, I think it was last week, there was an amazing supernova remnant that they came out with, an object that went off, I want to say, thousands of years ago. I’m too tired to remember exactly when. But now, we can see it expanding and colliding with the gas around it, and it’s just beautiful.
Fraser: And, you know, you sort of ruined my conclusion here because we were gonna talk about Spitzer. But, one of the things that really did tie together this idea of these observatories working as a unit were these images, some produced by Chandra, but also some were released with Hubble where they would take this series of images using, say, the Hubble space telescope, and then they would also observe the same region in x-rays or with Spitzer in infrared, and then put them all together with different colors. And then, you could see this is the stuff that is incredibly hot and bright, and then this is the stuff that would look as if we saw it with our own eyes.
And then, this is the clouds of dust that’s obscuring other parts from our point of view. And, that’s what I think is the real take-home about having this access to the entire electromagnetic spectrum is now suddenly, you see the stuff that you would normally see, but you also see all the stuff that you wouldn’t see that’s invisible. And each one tells a different story.
Dr. Gay: And, we got lucky. But, when Compton failed, they were already thinking ahead to GLAST which became Fermi to Swift, which fills a different role doing its images looking specifically for gamma-ray bursts and targeting their location using its many different wavelength detectors. There was this vision moving ahead of how we would fill in behind. And so, Fermi stepped forward, filled the role of Compton. Someday, JWST will step forward and fill in that role that Spitzer had bringing us, well, as Fermi brought us so much better views of the gamma ray universe, so too will, hopefully someday, maybe, JWST bring us better images than Spitzer.
Fraser: But, not quite, because Spitzer was colder. And so, Spitzer could see further into the infrared than James Webb will be able to. You know, James Webb doesn’t have that coolant on board. It just has an incredible sun shield to block the light from the sun. But Spitzer, there is nothing that can compare to Spitzer out there. I mean, apart from maybe ESA’s Herschel mission, which sort of fulfilled the same kind of role. And, the real successor to Spitzer is gonna be HabEx or those new missions in the works. It will be the true successor. So, let’s talk briefly about Spitzer before we run out of time. That was the last of the Great Observatories to launch in 2000.
Dr. Gay: In 2003.
Fraser: 2003. The year we started Astronomy Cast? No, wait.
Dr. Gay: No, we started in 2005.
Fraser: 2005. Okay. Okay.
Dr. Gay: No, no. Slacker Astronomy was 2005. We were 2006. Podcasting started in 2004. So, we did not launch with Spitzer.
Fraser: Right. Did not launch with Spitzer. Yeah. Okay.
Dr. Gay: So, Spitzer launched in 2003. It was an infrared observatory seeing those colors of light that, well, the Terminator uses to figure out where people are inside buildings while looking for their heat. This is a color of light we can’t see, but some insects and reptiles can. It went into colors of light even redder than what – well, what anything alive on our planet can see. And with those eyes, it was able to peer through clouds of gas, seeing all the stars that lurked behind because it turns out it’s the short wavelengths of light that dust is able to sop and, those longer wavelengths, those redder wavelengths are able to pass through.
So, there’s these amazing images of things like the pillars of creation, one of those canonical nebula that you’ve seen in everything from Star Trek to coffee mugs. Those images were taken with Spitzer where they appeared as nothing more than ghosts with stars shining through their structure.
Fraser: I think the most impactful images that I’ve ever seen from Spitzer, there were incredible images of seeing through nebula because you could see into the dust. But, the one that really hit me the hardest was the view of the Milky Way. There’s an incredible mosaic taken by Spitzer of the entire Milky Way, and the image is gorgeous, just beautiful. But also, because Spitzer could see through the gas and dust of the Milky Way, it allowed astronomers to actually start to see what was behind the disc of the Milky Way for the first time that we had never known. There was always the great attractor. What is this mystery? And, we can finally see it. We finally see the galaxies that were over there that were helping to summit us in a lot of galaxies towards this center of gravity.
Dr. Gay: And, I have to giggle every time I think of that image because one of the side effects of being able to see through all but the thickest gas and dust out there was we learned that our galaxy is sitting out there blowing bubbles left and right. There are all these beautiful spherical pockets blown empty that were just waiting to be discovered that are related to different parts of star formation.
Fraser: And so, we should talk about their endings. Hubble of course still going. Chandra is still going. When did we lose Compton?
Dr. Gay: Compton died fairly early. And, it had the saddest and most common fate a spacecraft can have.
Fraser: I wonder what it could be. What could have taken it out?
Dr. Gay: Yeah. So, back in 2000 when I was still a graduate student, it lost a gyroscope, only one. It still had others. But, the concern was that Compton was a dense enough spacecraft that if it came plowing uncontrolled through the atmosphere, chunks of it could do damage to something on the surface of this planet. And having dumped bits of spacecraft on Australia and having still found ourselves getting made fun of it, we weren’t looking forward to dumping more spacecraft on potentially other nations. So, the decision was made for the first time in NASA’s history to purposefully deorbit a spacecraft because they weren’t sure they could control the telescope with only one gyroscope. So, down she came.
Fraser: Yep. And, I wonder, though, later on, they figured out how to control telescopes with down a gyroscope. So, I wonder if they could have used some of that same methodology because, say, Kepler, they were able to figure it out. So, when did we lose Spitzer?
Dr. Gay: So, Spitzer, for all we know, may still be a tired, healthy, low energy spacecraft still lagging behind us. Spitzer was put into a really cool orbit that was super similar to Earth’s orbit, but, not identical. And as a result, over time, Earth crept ahead around the sun, Spitzer lagged behind orbiting the sun, and the two, because of their different paces, ended up going further and further apart as they circled and circled through the years. And, Spitzer just was really struggling to make itself heard here on Earth when they gave up science missions just last year.
Fraser: Yeah. So, we were in Hawaii for the AAS meeting when they sort of did the final announcement with the final discussion about Spitzer sort of doing, I guess, a postmortem talking about it. It was really sad because it, as I said, produced images – like, the Chandra images were nice, but in many cases, they were best when they were overlaid on top of a Hubble picture or a Spitzer picture.
Dr. Gay: Right. X-rays are not exciting people unless you think about how high-energy they are. You don’t get detailed details, for lack of a better set of words, when you’re looking at things that are simply sitting there blasting energy into the universe.
Fraser: Yeah. So, I came up with a way to talk about how we detect the electromagnetic spectrum when sort of thinking about the various observatories. So, when you hold out your hand to feel the heat coming from, say, a nuclear reactor, then that’s your sensing the infrared.
Dr. Gay: Do not try this at home.
Fraser: Do not try this at home. And then, of course, you can see it. You can see the nuclear reactor with your own eyes –
Dr. Gay: Before they melt.
Fraser: Right. As you get the burns on your skin – the sunburns, then essentially, your skin is an ultraviolet detector, and then I guess when the cancer shows up later on, that’s you detecting the x-rays. So, it’s pretty gross. But –
Dr. Gay: I don’t like this analogy.
Fraser: Right. But, that’s the way we could detect all of these wavelengths all at the same time.
Dr. Gay: No.
Fraser: Well, thank you, Pamela. It’s funny. My career in science journalism really went along with reporting on all of these observatories. Hubble had already launched, I guess, and Compton already launched, but I was there for Chandra. I was there for Spitzer, and there for the end of all of them. Hopefully, I’ll be there for the end of the last two and really good chance to see them through their entire life. It’s been – what wonderful machines.
Dr. Gay: It’s been an amazing journey.
Fraser: Yeah. Yeah.
Dr. Gay: We were the children of Voyager and the adults of the Great Observatories.
Fraser: Yeah. Yep. All right. Well, thank you, Pamela. And, we’ll see you tomorrow for the next episode.
Dr. Gay: Yes. Yes, you will. So, thank you so much.
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