Transcript: Dwarf Planets

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Fraser: Astronomy Cast Episode 194 for Monday June 14, 2010, Dwarf Planets. 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. My name is Fraser Cain, I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville. Hi Pamela, how’re you doing?

Pamela: I’m doing well. How are you doing, Fraser?

Fraser: Good! I hear you’ve been infested with groundhogs.

Pamela: We have a giant (just one) rodent of unusual size eating in our backyard, and it’s really, really cute.

Fraser: Awww, it’s adorable until they tear your whole yard apart… make it unusable.

Pamela: Yeah, we’ve already got moles and squirrels and yeah, I’m not worried.

Fraser: Just give it back to nature. Alright, well, in 2006 the International Astronomical Union demoted Pluto out of the planet club. But they also started up a whole new dwarf planet club with Pluto, Eris, and the asteroid Ceres as charter members. Let’s find out what it takes to be a dwarf planet and discuss the current membership. Alright, well now the first episode of Astronomy Cast was us talking about why Pluto is no longer a planet. I was hoping we could do an update… you know, Pluto back in the planet club…

Pamela: Nope.

Fraser: Nope.

Pamela: Nope.

Fraser: So then it’s really kind of official… let’s follow it up, let’s set it in stone. Dwarf planets… there have always been dwarf planets… there will always be dwarf planets.

Pamela: Well, there haven’t always been dwarf planets, but…

Fraser: We’re rewriting the history books now… alright, well let’s not talk about the history… so let’s provide a shorter version of what happened in 2006.

Pamela: Well, at a meeting of the International Astronomical Union it was decided that they needed to figure out what to do with all of these giant icy bodies in the outer solar system.

Fraser: Right. This was really triggered by the discovery of Eris… which is bigger than Pluto.

Pamela: …which is bigger than Pluto. Even NASA called it the 10th planet. So there’s a lot of people up in arms… “No, there aren’t ten planets!” My favorite argument of all is if we start calling all of these icy bodies planets, then there’s too many planets for the children to memorize. I’m like… but there’s 26 letters in the alphabet, and we make them learn those… there’s 50 states in America and we make them learn those…

Fraser: But I can imagine with the success of the icy body finders… the Kuiper Belt object discoverers… there was going to be more and more of these objects, so you would have from 2006 to 2010 there were 10 planets, and then from 2010 to 2015 there were 11 planets…. As the telescopes get bigger… especially, you can imagine what James Webb might be able to turn up… so it’s just a matter of time before they find more and more and more… are there 15 planets… 20 planets…

Pamela: That starts to become a matter of what makes a planet a planet. And this is where you start to get to logical arguments. The “well we can’t have that many planets ‘cause the children can’t memorize them,” that’s not a rational argument, people. But saying, well Ceres in the asteroid belt was considered a planet for 50 years before we started turning up other asteroids and realized oh, it’s part of a family of objects… let’s call the whole family asteroids. Well, Pluto was the first one found in the Kuiper Belt, and now we’re finding all these other chunks of ice, and well it’s now the Kuiper Belt. Demoting Pluto is sort of like demoting Ceres, we just realized “oh, it’s not really a planet, it’s part of this family of specific objects.” The analogy I always use is that if aliens were cleaning up our solar system and sorting things into bins, Jupiter, Saturn, Uranus, and Neptune—they’d get thrown in a bin. Then all the rocky stuff would more or less get thrown in bins. And all the icy stuff would more or less get thrown in bins, and who knows what they’d do with Mercury, Venus, Earth, and Mars… but those’d probably get their own stand-alone bin as well. So, yeah… we have all this icy stuff… not really planets… no, not physically planets… but for a certain class of objects—they’re all round, they’re in hydrostatic equilibrium, and Haumea isn’t exactly round because it’s spinning wildly… but it could be round if someone stopped it spinning. So now we look at physical characteristics.

Fraser: Right, so in 2006 the IAU decided to do something about Eris, and once and for all… so they came up with their three rules for planets.

Pamela: Right… something has to be in hydrostatic equilibrium, which means the sucker is round.

Fraser: So it has to be a sphere… so something like the Mars moons, Phobos and Deimos, they’re not round… they’re asteroids… they’re, as you call them, spuds. So those, even if they were going around the sun, they would not count.

Pamela: And the way they make an exception for Haumea is they look at it and acknowledge that if it were left alone, the self-gravity of the object would cause it to collapse into a round shape.

Fraser: So that’s rule number one, right? It’s gotta be round.

Pamela: Rule number two… it needs to be orbiting the sun. So if you have a giant object, orbiting Jupiter, does not count as a planet.

Fraser: And we do… we have Ganymede which is bigger than Mercury. So were it orbiting the sun, it would be a planet.

Pamela: But it’s not, so it’s a moon.

Fraser: So it’s out. But it is in hydrostatic equilibrium… but it doesn’t orbit the sun, so it’s out…. not a planet. So the third rule… the kicker…

Pamela: The kicker is it needs to have cleared out its own orbit. And this is where a lot of the controversy comes in. If you took Earth and put it out at the distance of Pluto, the huge volume of its orbit… the earth just wouldn’t be able to clear that out. So even the earth, in the Kuiper Belt, wouldn’t count as a planet. So this is where folks like Alan Stern start looking at the definition we have for a planet and start saying… no guys, we need to rethink this. We need to start classifying things based on the characteristics of the objects. And here’s where a lot more controversy comes in… what do you start requiring? And no one really knows. And everyone’s just sort of grasping at straws at the moment. But we know that we need to change the definition because the whole “must be orbiting the sun” part kinda means that things orbiting Eta *?* and 51 Peg and all these other stars out there, they technically aren’t planets.

Fraser: But you can just change it to “orbiting their star.”

Pamela: Right, but still that’s a change in definition. So while we’re rewriting the definition, let’s start to consider what other things do we need to put into the definition to make planets incontrovertibly planets.

Fraser: Right. What if they orbit a pulsar, right? What if they orbit two stars in some strange way… anyway, yeah I can see that it might get more complicated. Ok, we’ve got the three rules… it’s gotta be a ball, it’s got to go around the sun, and it’s got to have cleared out its orbit. What are the current dwarf planets?

Pamela: Currently, there’s five known dwarf planets…. five acknowledged dwarf planets. We have Ceres hanging out in the asteroid belt, and then of course there’s Pluto and its demoted self in the Kuiper Belt. We have Haumea and Make-make, and then there’s Eris. These are five very, very different objects, and there’s two more that a lot of people group in, but we don’t know enough about them. There’s Quaoar, which is utterly unpronounceable, and Sedna; and we just don’t know if these objects are in hydrostatic equilibrium, so we need better data to figure these two out. But, they probably are.

Fraser: And these objects are actually quite different… especially Ceres compared to the Kuiper Belt objects. So let’s take a look at Ceres first.

Pamela: Ceres… it’s a rock. It’s nearby; it formed right along the frost line of the solar system. It’s on the inside of the frost line; so when it formed, it actually formed without any volatiles. It looks like a moon. It looks a lot like our own moon. It has craters, it has variations in color on the surface; but it’s hanging out in the asteroid belt, leering over all the potatoes in its sphericalness.

Fraser: Right. Ceres is the largest object in the asteroid belt by far… it’s got a third of the mass… but it hasn’t cleared out the space around it.

Pamela: No… no. And it’s not actually that big once you start comparing it to some of the other dwarf planets. It’s radius is 487-ish km. along the equator. It’s 455 along the pole. It’s a lot bigger than all the other asteroids, but it’s not the biggest thing out there.

Fraser: And the cool thing is that NASA’s Dawn spacecraft is going to be getting to Ceres in 2015 after it explores Vesta next year.

Pamela: Right. So this means that we’re going to have two more dwarf planets getting explored in the not too distant future. And we also have New Horizons, so apparently we’re focused on sunrises and sunsets and horizons with these missions. We have New Horizons going out to visit Pluto…

Fraser: Also in 2015…

Pamela: Yes.

Fraser: That’s going to be a big year.

Pamela: And they’re looking for another target for New Horizons to go to after Pluto, so hopefully we’re going to be able to get two icy bodies for the cost of one satellite.

Fraser: So then we talked about Pluto [Ceres?-ed.], so we can kind of jump out then to take a look at Pluto… which is very different from Ceres.

Pamela: So Pluto… it’s a system… it has moons… it’s surface is pretty much solid ice. This is an icy body… it’s atmosphere comes and goes. When it’s closest to the sun, it has a very, very diffuse atmosphere. Then that atmosphere snows out when it’s at its most distant, and then its a nice atmosphere-less icy blob. One thing that I heard Mario Livio say once that I’m never going to forget is you can’t call Pluto a planet because if you gave it… and I’m paraphrasing… you gave it the orbit of a comet, it would grow a tail in the inner solar system and that’s not the way a planet should behave.

Fraser: That’s just not civilized.

Pamela: No, not at all. So, it probably has a rocky core… It is denser than water… but it has this icy outer layer, and yeah, if you brought it close to the sun, the sucker would grow a tail. It’s density is only 2 x 103 g/m3. That’s twice the density of water, so it’s still not that rocky of a rocky body.

Fraser: And Pluto has a moon that’s a significant portion of its own mass. In fact, the two objects, Charon and Pluto, they orbit a common center of mass. And so for a while there, there was a possibility that Charon would be considered a dwarf planet all on its own.

Pamela: Right. That was part of the argument actually… what do we start calling all of these things? They were throwing everything in… if it’s round, we’re going to call it a planet. So all of these smaller bodies were also getting considered, and Charon, they kicked out. And, this is where they start looking at secondary parameters. They start looking at the densities, they start looking at the… well, is it round because it hasn’t been beaten up that much, or is it round because this is its default shape due to gravity. With Charon, if you beat it up enough, it would stay in a deformed state.

Fraser: Oh, ok… so it just hasn’t been beaten up enough and so it’s got a fairly circular shape.

Pamela: Right.

Fraser: Ok, and then the next object out is Haumea.

Pamela: Right, and this one is just interesting in so many different ways. So first of all, it’s not round, as near as we can tell. Now we don’t have any perfect images of it. Instead, what we look at is how does it’s brightness vary over time. It’s thought, based on watching light curves as it rotates, that it’s probably much longer on one axis than the other, and this implies fairly fast rotation. Now, at the same time, because we don’t have any direct images, it could also be just another one of these strange objects that has two extremely different albedos. We’ve seen this on some of the moons out there. But it’s thought, no, this is actually something that simply has very different dimensions in the two axes… almost a factor of 2 difference. So looking at it, we make this guess at the shape, we make this guess at its rotation period, and as near as we can tell it’s a fast-rotating oblong object, and it probably just got the tar knocked out of it in a collision early on in our solar system’s past. Now this was the second giant object found out in the Kuiper Belt. It also had a fairly controversial beginning. The people who are normally acknowledged for finding it are Michael Brown and his team. But if you actually look at the official notice for it, it’s kind of confusing because it’s acknowledged as having been discovered at Sierra Nevada Observatory in Spain, but then it’s given the name that was submitted by Michael Brown’s team. If you read back about what happened, Michael Brown had been observing it, along with the rest of his team, and as they were pulling together all of their data, they nicknamed it Santa Claus, and they observed it multiple times… they were holding back with it and some other objects to have a really big release. They’d written an abstract that was submitted to a conference, and somehow a Spanish team got wind of it. They looked at the conference abstract… they did some Googling… they found the observing logs, which give you a sense of where on the sky the telescopes were pointed. Apparently Michael Brown and his team didn’t know their observing logs were public. So the Spanish team, knowing an object had been discovered, knowing the rough area on the sky where it had been discovered, went back through some archival images… back to 2003 archival images… found the object in the archival images. They did follow-up observations based on the positions of Michael Brown’s team’s observing logs… rediscovered the object using the predictions and then sent in their results to the Minor Planet Center. Now this put the Minor Planet Center in a horrible position because… well, initially, Michael Brown sees a discovery of one of his objects, kind of does the “oh, no, other people are looking at the same things I am…” rushes Eris, which is bigger than Pluto and really important to him, to publication. And this was like on a Friday afternoon, and a bunch of us looking at the press releases were like, “Wait, huh? Press release Friday afternoon? This makes no sense, there’s some story behind this.” And Michael Brown… he took the high road… he congratulated the Spanish team. He admitted… Yeah, some folks looked at my observing logs and that’s why I rushed Eris to publication… really sorry to step on your thunder. But the Spanish team didn’t acknowledge that they were the ones who looked at his observing logs, and he figured that out later. He ended up lodging a complaint, and so the announcement and the naming of this object really got held up in the politics of trying to figure out who do we give credit to. They ended up giving credit to both teams by naming the observatory from the one team and using the name from the other team. It was David Rabinowitz who came up with the name. It’s the matron goddess of the island of Hawaii where Mauna Kea Observatory is, where their team was observing it. But it was just a political mess. As near as anyone can tell, having public data logs is a really bad idea when you’re discovering objects. The Spanish team read the observing log, realized that no one had published the discovery yet, and stole it.

Fraser: …is the allegation.

Pamela: Is the allegation.

Fraser: Right. We have no proof either way. So next is… so you’re saying it’s Makemake, or not?

Pamela: I think it’s Makemake… it rhymes with bake…

Fraser: Right. Makemake.

Pamela: Right, it’s not a fish dish… I keep trying to turn it into one…

Fraser: Mmmmm. This one was discovered by Michael Brown and team.

Pamela: Yes. This one was announced back in 2005. It’s the third largest known dwarf planet… it’s a big ol’ object. It’s on a really weird orbit… it comes in as close as 38 ½ AU and goes out as far as 54 AU, so it’s really elongated. It’s a rock… well, actually it’s a block of ice.

Fraser: It’s a block of ice… it’s a snowball.

Pamela: It’s a block of ice. Yeah, it’s not the most exciting of them…

Fraser: Yeah, there’s not a lot that’s very interesting… so let’s just move on…. to Eris.

Pamela: Well, Eris… this is where we get into the big controversy… For almost a year it got referred to as the 10th planet, even by NASA.

Fraser: Or Xena…

Pamela: Or Xena… that was the other one that was particularly cool… it’s code name was Xena and it has a moon, so it’s code name for the moon was Gabrielle. I think everyone was really hopeful that silliness would prevail, but…

Fraser: But it didn’t.

Pamela: No!

Fraser: Although the name that they came up with was pretty great.

Pamela: The name that they came up with was pretty great. It was almost kind of sad, though, because Michael Brown’s daughter was born at the same time, and her name was Lillith. Rumor has it that he wanted to name it after his daughter, but that wasn’t allowed. So the dwarf planet’s name is Eris. It’s moon’s name is Dysnomia, and we were lucky to be able to find it when we did. This is again an object that has an extremely elongated orbit, comes in to about 38 AU and then goes out to 98 AU, and it’s not visible out there. It’s orbital period is actually 557 years. Brown and company… Brown and Trujillo and Rabinowitz… they were lucky to catch it when they did… ‘cause it’s on its way in right now, it’s on some of its closest approach, and we get to observe it, and then it goes away for awhile.

Fraser: So it gets as close as 37 AU and as far away as 97 AU… that’s a big difference between its closest point and its most distant point.

Pamela: Yeah.

Fraser: And it’s got a moon, and it’s bigger than Pluto.

Pamela: And it’s a lot bigger than Pluto… that’s cool. It’s dense, it’s big, and it’s on a really weird orbit… this is one of those objects that leads people to really start trying to figure out what could cause these weird things. But there are weirder objects lurking out there still awaiting final classification.

Fraser: And so with the five dwarf planets, and 2 or 3 provisional ones… the two Sedna and Quaoar are pretty close. Maybe with better observations, seeing their orbits for longer, maybe discovering a moon… that’ll make a big difference.

Pamela: Right.

Fraser: But it really is just a matter of time before more of these large Kuiper Belt objects are turned up.

Pamela: And that’s what’s so amazing is so, for instance, Quaoar… it’s a rock. It’s a known rock. There’s a great post over on Emily Lakdawalla’s blog… The Planetary Society Blog… titled “Quaoar: A Rock in the Kuiper Belt” where she pulls a bunch of these images where they were looking to see its moon and trying to figure out its mass. It’s moon is named Weywot, which is just fun to say. So they’re out there, they’re trying to figure these things out, and as they look at them… Quarhar… we don’t know where this rock in the Kuiper Belt came from, and that leads to a lot of questions about dynamics. We look at Sedna that has this really weird orbital radius of 509 AU, this is another object we were lucky to catch when we did.

Fraser: That’s five times further away from the sun than Eris.

Pamela: Right.

Fraser: And more like ten times further away than Pluto, but happens to be at the closest point of this really elliptical orbit.

Pamela: And so we look at these things and start wondering well what gravitationally could cause something like this… and there’s some folks working on planetary orbits who figured out, well, there could easily be an Earth-sized object, a Neptune-sized object, a Jupiter-sized object, out thousands of AU from the sun just waiting to be found. And of course there’s the eternal search for Nemesis, a small dwarf star that’s orbiting our sun, waiting to be discovered. So there could be more things that we’d recognize as planets waiting to be discovered, just not reflecting a whole lot of light.

Fraser: So it’s really just a matter of time… so we’ll be updating this show, somehow, as we go… In ten years when we have episode 500 of Astronomy Cast… we’ll have probably more dwarf planets by then. Especially with the launch of the James Webb Telescope, so stay tuned. Alright, well thanks a lot, Pamela!

Pamela: Sounds great, Fraser. Talk to you later.

Transcript: Astronomy with the Unaided Eye

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Fraser: Astronomy Cast Episode 193 for Monday June 7, 2010, Astronomy with the Unaided Eye. 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. My name is Fraser Cain, I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville. Hi Pamela, how’re you doing?

Pamela: I’m doing well… it’s so good to be recording in the same month that we’re existing in!

Fraser: I know… I know… Yeah, the summer of episodes is grinding on and we’re pretty much caught up, and we hope to get ahead because you’re going to be travelling like crazy in July.

Pamela: Yes, if you’re going to be at TAM, I shall see you at TAM. If you’re a scientist and going to be at the NASA lunar forums, I will be at the NASA lunar forums. If you’re an educator and you’re going to be at the Astronomical Society of the Pacific meeting, I will be at the Astronomical Society of the Pacific meeting. And then both Fraser and I will be at DragonCon…

Fraser: In September…

Pamela: In September… and then both Fraser and I will be at the US Science and Engineering Festival in Washington DC in October.

Fraser: There you go. Ok, so we talk a lot about telescopes here at Astronomy Cast, but you don’t really need any special equipment to appreciate what the night sky has to offer. Just head outside with some sky charts, maybe a planisphere, some friends, and hot chocolate, and you’re good to go. Let’s talk about what kinds of things you can see with just your eyes. And before we did this episode… the real title should be “Astronomy with the ***** Eye,” not “Astronomy with the Unaided Eye.” But…

Pamela: But there’s spam filters…

Fraser: The spam filters! I know! So, this is the thing, right, we say that… we put that as our title, then kids won’t be able to access this site because their nanny filters will go off, in fact, whoever’s doing the transcript for this…

Pamela: Don’t use the word *****.

Fraser: Leave this whole part out… it’s not even in there… so, as a web-master, this is one of the sort of little pieces of experience that we’ve built up is to never use that word when we’re talking about astronomy with the unaided eye. So, unaided… meaning no binoculars, no telescope, just your eyeballs enjoying astronomy.

Pamela: And if any of you have problems with nanny filters and my last name… this just occurred to me… some of you may be having that issue. Let us know and we’ll figure how to work around it…

Fraser: That’s true, yeah. Ok, so… I love doing this. A lot of my favorite part of astronomy is just being able to go out, take some friends outside, show them the constellations, especially when really interesting things are happening. So what kinds of things, like general class of things, can you see just without any telescope, binoculars, anything?

Pamela: The most amazing thing… and this requires going out in the dark somewhere… like really dark… like drive so that you can’t see a city on any skylines. Drive to the middle of nowhere, take a tent, take a sleeping bag, take friends, take food and water, and look up in the summer and just absorb the Milky Way.

Fraser: Yeah.

Pamela: It’s the most amazing thing. And if you’re in the southern hemisphere, the dust lanes through the Milky Way… at one angle it looks like an emu… at another angle it looks like a floppy-eared dog. And you can actually lay there with your friends and spend the entire night going, “And the dust lanes look like…” and just making stuff up like you’re looking at clouds.

Fraser: And so what are these dust lanes that we’re seeing?

Pamela: Well, it’s a combination of… first of all there’s this bright stripe through the sky that’s the equivalent of where the disk of the Milky Way is. So we live embedded in a pancake of material. And if you can imagine holding a giant 10-foot diameter pancake up with a hole off-center and sticking your head in the hole… where you look around and see pancake, that’s the disk of the Milky Way in the sky. Now, just like you can’t look all the way through the pancake because there’s pancake material, you can’t look all the way across the disk of the Milky Way because there’s dust. And so when we look out, where we see really bright, it’s literally thousands and thousands and thousands of stars packed side by side, lighting up this bright stripe. But there’s also lots of dark molecular clouds, lots of cold gas, lots of stuff out there that’s just blocking the starlight. And the dark bands through the Milky Way is where it’s particularly dusty.

Fraser: So, to see the Milky Way, you definitely have to get out of the city, you have to get, I would say, 30-40 kilometers away from a city to really start see it. We can see it where I live. I live in a city, but it’s not a very bright… not a very large city. And still, the Milky Way doesn’t look that nice. And if I go a few kilometers out of the city, then things get a lot darker and a lot better.

Pamela: Yeah, where I live in southern Illinois, I can’t see it from my house, but I have a horse… an old, mangy-ish… not really, he’s very cute… I have an old horse… and the barn where I keep him… if I hang out too late, I can see the Milky Way out there. So, if you have a friend with cows or horses, likely if you’re out at their barn and you shut the lights off, you can see the Milky Way.

Fraser: But I think in general, everything that we’re going to recommend, the further you get away from the city the better. Whether you’re seeing comets, meteor showers, the planets, anything… get away from the city. And also, the later you stay up, the better it gets. So, you know, if you’re gonna start to see some stars… 10 o’clock at night… it’s a completely different story when it’s three in the morning.

Pamela: Yes. And well the other thing with three in the morning is that people shut off all their house lights, so as people go to bed, the sky gets darker and darker as all of the lights get turned off, and you can actually see that in how many stars you can see.

Fraser: Yeah, one thing that I’ll do when I take the kids camping is we’ll just go to bed at a normal time, but I’ll set an alarm and then, yeah… at two in the morning I wake up everybody… I wake up the whole family. And they’re like, “I don’t want to!” And then I show them the stars and they’re like… “Oh, yeah, this is good!” And then if we’re watching a meteor showers, etc., then that’s what we’ll do. Then you can really appreciate it. Then it just blows your mind.

Pamela: And this is the year for the meteor showers, and we’re starting to come up on it. I know you’re looking forward to August.

Fraser: Yeah, August 2010… so if you’re listening to this after that, I’m sorry… you missed out. But August 2010, the Perseid meteor showers are going to be just 2 days away from a new moon, so you’re going to have the darkest possible skies, plus you’re going to have a triple conjunction… you’re going to have three planets very close to the moon… I think it’s Jupiter [Saturn], Venus, and Mars are all going to be very close to a crescent moon. And then you’re going to have the Perseid meteor shower. So, right now… put on your calendar…

Pamela: August 12-13…

Fraser: August 12-13… the 13th is a Friday, so, you know…

Pamela: You can go out and celebrate your superstition with a doubly superstitious night.

Fraser: Well, no, but also you don’t have to work on Saturday so you can stay up really late.

Pamela: Yeah, and they’re estimating 60 meteors per hour with this one, which is fairly consistent… and the Perseids often put on a nice bright show.

Fraser: Yeah, really bright one. So, make sure you do that. Find some friends, schedule a time, go camping the 13th of August, 2010… or 12th… it’ll be fine. Ok, so we’ve talked about the Milky Way… what else can we see with just our eyes?

Pamela: Well, it varies with the year. Not with the year… with the time of year. Since we’re in summer, we might as well start with summer. One of my other favorite objects to search out… there’s two of them actually… the easier one to find is the Andromeda Galaxy. You can actually see it as this fuzzy… wow, is there really something there? Wait, if I turn my eyes sideways… wow, there’s something there. If I look directly at it, it kind of disappears. You have to learn how to use your off-center vision to see it best. But, Andromeda actually shows up as something fuzzy the size of a fingernail up on the sky, and that’s about as cool as it gets.

Fraser: Isn’t that about the most distant thing you can see with the unaided eye?

Pamela: In the northern hemisphere, it’s the only galaxy that can be seen by normal people on a regular basis, ***** eye, and it just really stands out. It’s off the legs of the constellation Pegasus, and it’s fairly easy to see. It’s going to be a really late-night object this time of the year. Then it gets higher and higher in the sky as we get towards fall. But right now, early in the morning, it’s up as a morning object… those of you who see the sun rise, just get up a little bit earlier and it’s there waiting for you. The other object, though, that is perfectly high in the sky right now is M13. This is a globular cluster, so it’s something that’s out of the disk of the galaxy. It’s literally a cluster of thousands and thousands of really old stars packed into a tight ball that if you did look through a telescope, would kind of look like a dead bug splattered on the eyepiece. It’s in the constellation of the Warrior, and there’s just this fuzzy splatter print on the Warrior’s chest.

Fraser: That’s Hercules, right?

Pamela: It’s Hercules… it’s in the constellation Hercules.

Fraser: And you can see the Summer Triangle, which is actually made up of three different constellations, but in the summer, it’s your go-to constellation first.

Pamela: And it helps you find the Milky Way, because the Milky Way goes right down the center of the Summer Triangle. So the three corner stars are Altair, which is in Aquila, the eagle; Vega, which is in Lyra, which is a type of harp; and then Deneb, which is in Cygnus, the swan. Aquila and Cygnus are both flying along the Milky Way.

Fraser: Right. And so, in the summer anyway, they will be pretty much the three first stars that you see. And then you can watch them over the course of the night as the rest of the constellation fills in. So summer… and then of course in summer, later on in the evening, Perseus comes in quite nicely.

Pamela: Right.

Fraser: Which looks like, from my vantage point anyway, an upside-down V.

Pamela: And between Perseus and Cassiopeia there’s the Double Cluster, which is another thing that if you’re in a dark, dark, dark, dark site you can sort of go… oh, there’s something there.

Fraser: Yeah. Then you look at it and it disappears. Something faint…

Pamela: But Cassiopeia is always striking to look at because it’s either this big number 3 or this big W or this big letter M, depending on what time of day it is. And there’s people who actually learn how to tell time as a function of where in the year we are by looking at Cassiopeia. It’s really neat to take these very linear constellations that are up all night, and watch through the night as they rotate through the sky. You can also do this with the Milky Way in both the northern and the southern hemisphere. As you watch the Milky Way through the night, it will slowly rotate through the sky, which is just fun.

Fraser: And it’s the summer right now when we’re recording this, but there are other things that look quite great over the course of the year… although it gets colder, anyway for us… to go outside…

Pamela: So just to bring one more thing up as we stay in the summer is that if you live near the equator, you are a lucky soul. The object I’m about to mention can be seen by most of both hemispheres, and that’s Sagittarius, the teapot. Although in the southern hemisphere it wouldn’t hold any water.

Fraser: Upside-down teapot…

Pamela: Yes.

Fraser: But it sure looks like a teapot… absolutely… no question.

Pamela: Yes, and imagine just taking your little kids out, and you can do the “I’m a Little Teapot” song and show them where on the sky the spout is and the handle is. It’s just a neat way to engage little tiny kids in astronomy. And Sagittarius, when you’re looking at it, you’re looking at the center of our galaxy. You can actually start to figure that out because as you look at the Milky Way, you can see how it’s much wider when you’re looking at Sagittarius, and then it narrows further away.

Fraser: Right. And then at other times of the year?

Pamela: So, moving into the fall, Orion starts to join us in the sky. We have Andromeda high in the sky overhead, and we’re just losing Sagittarius come September… it’s a very early evening object and sets very quickly.

Fraser: Orion is coming… Orion is great! I mean, once you learn Orion you’ll see Orion’s belt, you’ll make out the shape of the shoulders, even his shield and sword. And then inside the sword is the Orion Nebula, another one of those blurry spots on the sky.

Pamela: And what’s really cool about the fall sky is you can go out and you look at the Orion Nebula, the fuzzy sword, and those are stars that are still in the process of pulling themselves together. There’s going to be supernovae in the future of all these young bright, bright blue stars burning themselves out and exploding, but they’re not there yet. The stars are still in the process of forming with the smallest ones. So as you look at Orion, that’s a star-forming region. It’s going to become an open cluster… cc open cluster in the making, I guess. But then if you just look a little to the west, closer towards the ecliptic, towards the constellation Taurus, the bull. In that general direction, if you keep going past Taurus, the bull, you get to the Pleiades. This is an older open cluster, where all the stars have formed, where almost all the gas has been consumed or blown out. You’re now looking at the Subaru car symbol, and you’re seeing what Orion will become in the future. The stars are a little bit more spaced out… and it even gets better. If you now go back to Taurus, and you pause at Aldebaran, the big burnt-orange star… University of Texas… symbol is the bull… Taurus is a bull… burnt-orange University of Texas star… can you tell where I got my PhD? This is where the Hyades cluster is. As you’re looking at Taurus, there’s this over-density of stars that’s kind of spread out, and that’s what the Pleiades will become in its future. So here we’re looking at three different versions of the same object, at three completely different ages. All within a few fists of one another on the sky, this whole set of stellar evolution traced out.

Fraser: And a little later into the winter, we start to get Sirius coming up in the night sky, and that’s the brightest star in the night sky.

Pamela: Right. And it’s also a star… and you can never make this out with any normal human telescope or your eyes, let alone… Sirius also has a white dwarf companion. So when you’re looking at Sirius, you’re actually looking at two stars… a normal star and a little white dwarf beside it.

Fraser: And then what about into spring?

Pamela: So, as we get into spring, well now we have Gemini, the twins Castor and Pollux, straight overhead. And Cancer is out, and Cancer… if you’re in a dark site and you look at it, there’s this triangle of stars that you can just make out. In the center of this triangle of stars is this fuzzy cotton ball. And that fuzzy cotton ball is another cluster—it’s M44. And it’s just really dramatic in dark-enough skies. When I was down at Sutherland Observatory in South Africa a few months ago, I had to ask somebody, “What’s that big bright fuzzy thing over there?” just because it was just so shocking and I hadn’t been in skies that dark when Cancer was up. So that’s something very dramatic. It’s interesting to watch as the year progresses, just seeing how everything changes, because come March, we still have the Pleiades in the sky… we still have Orion… but they’re now in completely different places. It’s that march of the constellations that a lot of people just don’t notice. When you take the time to notice it, every year it’s like you get to watch your friends come back in the sky.

Fraser: And those lucky ducks that live in the southern hemisphere have a whole bunch of stuff that we just have no way of seeing in the north.

Pamela: Right. And it’s really shocking if you go to a dark site in the southern hemisphere because the Large and Small Magellanic Clouds look like someone took a fist full of Milky Way… tore it off and threw it to the side. Literally it’s like a fist on the sky worth of extra stars.

Fraser: Wow. And you can see Alpha Centauri, which is the system that contains the closest star to Earth, which we can’t see from the north.

Pamela: And the Tarantula Nebula… now I know this is supposed to be all unaided observing, but the one object that if you’re in the southern hemisphere, if you visit the southern hemisphere, if you think about visiting the southern hemisphere, you should go for this reason. If you look through just a 12-inch telescope at the Tarantula Nebula, you’re actually looking at the face of a tarantula. It really surprised me… it’s just like… big face, staring at you through the eyepiece.

Fraser: So we’ve talked about some things that we can kind of see all year long, quite dependably. So if you go out in August, you’re going to be able to see the Summer Triangle every year. What kinds of resources would you suggest people take to find their way around the sky?

Pamela: The best thing you can possibly do is either print out the monthly sky maps that you can get at skymaps.com. They’re good, they’re solid, they update them every month… they’re free! They tell you where the planets are. One of the things that periodically throws me off is Leo the Lion periodically grows a nose that’s just a planet that wandered across the ecliptic. It’s good to have sky maps to show you what these strange, mysterious additional stars and constellations are.

Fraser: Yeah, so free… go to skymaps.com, you can print off some free sky charts, and you’re set. Or if you want to spend a little money, get a planisphere or even… I like Nightwatch… as a book…

Pamela: Yes, Nightwatch is good. And there’s a yearly… if you love big, beautiful, stunning art, there’s a yearly sky calendar that comes out that you can get through Sky and Telescope that is super-sized. It’s about 18 inches tall, and just has the most amazing artwork. It updates you on every year’s… how good are the meteor showers going to be… The meteor showers can vary a couple of days each year. I was born during the Geminids meteor shower, but it’s not every year on my birthday.

Fraser: Right, and this was the second part that I wanted to talk about which is that some things happen on very specific days. These are the meteor showers. You can go out any day in August and see the Summer Triangle… you don’t have to be that precise about it. But if you want to see the Perseid meteor shower, then you do have to really go out within a couple of days. So there are meteor showers that you can see… what are some other objects that we can see?

Pamela: Well, one of the neat things to challenge yourself to do each month is to be the first person to see the crescent moon. There is nothing quite as magnificent low on the horizon as a couple-day old moon that is visible only just as the sun is setting. So, that’s a fun challenge. Then there are the times when a moon and planets are side by side on the sky. These are just random events that have beauty and you can go out and it’s neat to think that I’m looking, right now… at the same time… at Mars, Venus, and the moon. And that’s kinda cool. A few years ago Jupiter passed in front of the Beehive Cluster and so you get these merging of different events. Then there’s also solar and lunar eclipses as well. We’re going to have a partial lunar eclipse coming up on June 26, a solar eclipse coming up on July 11, and another lunar eclipse coming up on December 21. And with these good star charts, they can help you keep attention to when are all of these different things going to happen.

Fraser: And you can also see some stuff that are man-made as well… there’s satellites. If you spend any time looking up at reasonably dark skies, you’re going to see satellites go overhead. One of the games that we play is “Who’s the first person to spot a satellite?” Then, if you’re organized, you can go to the NASA website, and you can find out times when the International Space Station is going to be flying overhead… or the space shuttle… or Hubble.

Pamela: And another good resource to go to that also lets you in on the iridium satellites and random spy satellites and even comets is heavens-above.com. You can put in your location, specify latitude and longitude… Google Maps will help you figure that out… and it will tell you all of the cool stuff with ten days worth of predictions of what is going to be over your place on the planet. And there’s for some cities Twitter feeds set up by Rob Simpson of Orbiting Frog, so if you’re in New York City, for instance, you can go to Over New York. If you’re in Paris, there’s Over Paris. There’s a whole variety of different cities he’s set up, and I think he’ll often set up new cities if there’s a bunch of people who are interested. These will Twitter at you when a satellite is overhead that you’re able to see.

Fraser: Yeah, once again I would really recommend going to the NASA site, find out when the space station’s going to be flying overhead. Then schedule a party… schedule a time that you and your friends are going to be outside… you’re having a barbeque… then it gets late, and you have the timer go off and you go “Ok everybody… the space station’s going to go overhead!” You gather everyone around and you look up and right on cue, this super bright star shows up over the horizon and crosses the sky in about a couple of minutes and it’s gone. Everyone will think you’re a genius!

Pamela: And there’s also just neat things that we can’t always predict how cool they’re going to be like comet McNaught. Last year comet McNaught just came out of nowhere. No one knew how fabulous this comet was going to be. It’s back again this year… it’s just barely visible… it’s magnitude 5.6… it’s hanging out next to Perseus right now. But there’s often comets that crop up at least once or twice a year that are easily seen with unaided eyes, and it’s just really cool to go out and see these pieces of ice that might have originated in another solar system.

Fraser: Yeah, and once a decade you’ll get a comet like Hale-Bopp or Hyakutake. And with those, you’ve really got to get organized and get out of town, and see that with dark skies. A friend of mine and I went on a road trip to get out of Vancouver to see Hale-Bopp and it was just astonishing to see that comet on the horizon…. just amazing.

Pamela: And comet Hale-Bopp is one that when it was up, you looked at it and it was a large chunk of your windshield. And then when Hyakutake was out, I was observing at McDonald Observatory and I remember that it just happened to always be in my windshield when I was driving toward the observatory, so I felt like I was following the comet to the observatory. It was literally half my windshield wide looking at it and just hung low over the horizon, truly magnificent objects, but they only come around every few years. So keep an eye out for when they’re around and then just go absorb the experience.

Fraser: And I would also recommend getting to know when some planets are in the sky. We’ll usually announce some really interesting stuff on Universe Today, but there’s other sites as well. You can say… ok, and get to know… then you see the really bright Venus on the horizon or even high up in the sky even a few hours after the sun’s gone down. Then you just tell people. I will point a person towards Venus and say “Hey, did you know that’s Venus?” And they’re like… whoa, I didn’t realize that I could see Venus… and then “Yeah, and there’s Jupiter over there.” If it’s off to the west in the evening, it’s probably Venus. If it’s high up in the sky and it’s bright, it’s probably Jupiter. They’re the first things to show up. If it looks quite red, it’s probably Mars.

Pamela: And because Fraser and I both know the email is coming again… you will, at some point in the coming months as Mars rounds its way back around the sun, get the email—and Fraser knows what I’m about to talk about—saying that Mars appears bigger than the moon. That will never happen. So when your friends send this to you… you, too, can laugh at them, and then take them out and actually look at Mars, because Mars is cool to look at. It is so amazingly red and most people just don’t realize that you can actually see colors in the stars… and there’s reds and there’s blues and you do see the color… except for green—there isn’t green.

Fraser: And there’s a little bit of astronomy that you can do during the day… which is that you can observe the sun but…

Pamela: And the moon…

Fraser: And the moon. That’s true, but you can observe the sun, just don’t use your eyeballs directly. But, you can use a pinhole projector to project the disk of the sun onto the white piece of paper, and you can actually see sunspots. But don’t look with your eyes… don’t look with your eyes!

Pamela: Resist the temptation…

Fraser: Yeah. Well, that was great, Pamela, I think we… is there anything else that we can see?

Pamela: I think we hit the highlights. Go out and fall in love with the stars.

Fraser: So, right now, schedule the Perseids on August 12-13… get some friends together… do a sleepover… stay out late… leave the city… go camping…

Pamela: Remember bug spray… remember bug spray…

Fraser: Sure… and see the Perseids because you’ll remember it your whole life.

Pamela: And we’d love to hear your experiences on the BAUT forums where we have the Astronomy Cast pages.

Fraser: That would be great. Or, just send us an email, and that would be great. Alright, well thanks a lot, Pamela. And I’ll see you outside!

Pamela: Yes! Sounds good, Fraser. I’ll talk to you later.

Transcript: The Chandra X-Ray Observatory

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Fraser: Astronomy Cast Episode 192 for Monday May 31, 2010, The Chandra X-Ray Observatory. 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. My name is Fraser Cain, I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville. Hi Pamela, how’re you doing?

Pamela: I’m doing well, how are you doing Fraser?

Fraser: Very well. Now you and I were just talking about this, but we just want to remind all of our listeners that we are going to be at DragonCon…

Pamela: Labor Day weekend…

Fraser: Labor Day weekend… in Atlanta, Georgia. It’s a great party. 20,000 people there… amazing costumes… we’re going to do a live show… we’re going to be on panels… we’re going to be, like, wandering around aimlessly… looking for people to go out for lunch with… So, yeah, if you’re going to be coming to DragonCon, we’re going to be there.

Pamela: And looking a little further ahead in time, for those of you who like to plan ahead, like we do, in October we’re going to be at the US Science and Engineering Festival. There’s a National Mall outdoor event on October 23 and 24, and I’ll be in a Galaxy Zoo booth, also with Moon Zoo and other Zooniverse projects, and Fraser and I are going to be doing a stage show event. So come and support the show, see the two of us live, and check out all the amazing exhibits. Anyone who’s anyone doing science is going to be at this amazing event letting you play with their science.

Fraser: We’re going to find out if we can translate a podcast to a stage show… that’s the question.

Pamela: I think we’ll be ok.

Fraser: My money’s on “yes.” Alright, let’s get on with the show. So the Chandra X-Ray Observatory is the third of NASA’s great observatories, sent into space aboard the space shuttle to view the universe in high-energy x-ray radiation. This is the territory of supernovae, super-massive black holes, and neutron stars–some of the most extreme places in the universe. Now I actually started Universe Today back in 1999, and so within like 3-4 months of when I started working on the website, Chandra launched on the space shuttle. So I have a real good connection… I’ve been reporting on Chandra now for like 11 years…

Pamela: That’s amazing…

Fraser: Yeah, I know… so as observatories go, this is the one that I’m actually quite familiar with, with a lot of its research, and so I’ve seen the things come out of it. But for those who haven’t been reporting on it for 11 years… and once again, last week we talked about Chandrasekhar the person, and now we’re going to talk about Chandra the X-Ray Observatory… Chandra the robot, based on the man. So, let’s go back in history and take a look at the concept of Chandra. What’s the idea here?

Pamela: Well, back in the ‘70s, NASA started putting together plans for a set of great observatories. They ended up with four different missions, the Hubble Space Telescope was the first to go up, then there was the Compton Gamma Ray Observatory, which I think says that there’s probably a fourth dude named Compton in our future. Next to go up was the Chandra X-Ray mission, and then Spitzer was the last of the great observatories. Now Chandra… the idea for the mission… and it was originally the AXAF mission… the absolutely unpronounceable acronym mission… it was really conceived and proposed to NASA in 1976. The idea was put forward by Riccardo Giacconi and Harvey Tananbaum and it was to fill a gap in our ability to understand the universe. There’s so many things that give off x-ray emissions… shocked gases, compressed gases in clusters, gas that gets heated up as it falls into black holes, all these things—they’re emitting x-rays. Stars emit x-rays. And we couldn’t see it! And not being able to get information is annoying, and so they started in the late ‘70s and through the ‘80s and ‘90s working to design this amazing telescope that allows half arc second resolution of x-rays. Just learning how to focus x-rays has been a challenge.

Fraser: Right, and we can’t see gamma rays because they’re blocked by the atmosphere as well. So, I guess that’s why the Compton Gamma Ray Observatory was put up. But unless you build a space telescope, you’re not going to be able to see any x-rays at all.

Pamela: Right. And so we had to figure out how to build, how to focus, how to understand all that was needed to detect x-rays. It took a while. A lot of the work was done at the Smithsonian Astronomical Observatory at Harvard, and today, in fact, Chandra Center is located in Boston with joint support from the Smithsonian, from MIT, and at the Chandra Center. But they figured it out, and the science that’s come out of this mission is truly amazing. When I started graduate school, black holes were one of those things that everyone knew existed. But…

Fraser: Mathematically….

Pamela: Right. And we all pointed at the same couple of binary systems saying, “That probably is a black hole.” As I imitate older, male faculty members… but there was no evidence, and that is so annoying! But with Chandra, we were finally able to start looking at things and say, “That’s the signature of a black hole.” And that was perhaps the first really amazing thing Chandra brought us.

Fraser: So how did Chandra get up into space, then, because, I mean, you’re…

Pamela: I did skip a step. We do need to launch the mission, don’t we?

Fraser: Yeah, yeah… sorry, don’t mean to rein you in, there…. it’s very exciting… I can’t wait… but let’s at least talk about how it made it into space.

Pamela: It was actually launched on the space shuttle Columbia. The early great observatories were all designed for space shuttle launches. The original thought was to grab them, bring them back down to Earth, do things to them, and take them back up periodically. With Hubble, it got left up there and continued to be serviced by the space shuttles, most recently last year, but with Chandra there were some changes to it towards the end of the design cycle, and it was actually put into a highly elliptical orbit that would cause it to spend most of its orbit out beyond the Earth’s radiation belts. The Van Allen radiation belts are actually fairly damaging to the instrumentation on Chandra. They actually had to remove one of the instruments from the focal plane when going through the Van Allen Radiation Belt to help protect it from getting zotted by too many rays. So it’s now in an orbit that takes it a third of the way to the moon once per orbit and then cycles back closer to Earth and that’s usually when we get the data, but it can’t be serviced. But remarkably enough, this mission that was planned for five years has had an extended mission and has now planned to go for ten years… well it’s already surpassed ten years actually, it’s now 10 years and 10 months along… it’s estimated that it has at least a 15 year life expectancy at this stage. So that’s pretty amazing… it’s another one of those missions that was built and built well and is extending far beyond what was hoped for initially.

Fraser: Alright, now you can talk about the science.

Pamela: Thank you! So it allowed us to find where are the black holes.

Fraser: Right, but I mean obviously black holes are black… they absorb all the radiation—I’m assuming even x-ray radiation so how can Chandra see a black hole?

Pamela: Well, the neat thing is when you shock gas hard enough, it gets hot. And hot gas starts emitting in the x-rays. And so when we look towards black holes, we see both material that’s getting destroyed as it falls in… it flickers in the x-ray, and also, much more interestingly, we end up seeing these bubbling shock waves of material around black holes where, as you look in, you’ll see it literally looks like soap bubbles in the x-ray where when the black hole was active… when it was feeding… when something was getting destroyed… the process of having the matter get sucked in is highly energetic. It’s highly luminous as well, and all that light pressure, that radiation pressure, can clear out bubbles, and these bubbles… the edge of the bubbles pushing outwards shocks the gas that the bubble is hitting. So you have radiation pressure going outwards, just like air going into bubble gum. And the edge of the shock bubble is where the radiation is colliding with the interstellar material. And these beautiful bubbles are found in our own galaxy, they’re found in other galaxies, allowing us to know not only do we have the black hole Sag A star which Chandra discovered from its x-ray emission before we were able to image the stars orbiting so closely to it, but we’re also able to see these same amazing really cool structures in other galaxies.

Fraser: So, if I understand correctly, we’ve got a super-massive black hole, it’s feeding on material, the material is crushed around it so tightly that it’s becoming like a star around it… nuclear fusion is getting going, and what you end up with is the light pressure blowing out of this mutant star… this temporary star… and that’s blowing out cavities around the super-massive black hole.

Pamela: Right. This is talked about as black hole blow-back. And there’s some really, really amazing images in the Chandra galleries.

Fraser: And so this is some of the more exciting stuff… you’ve got black holes, you’ve got these high energy x-rays streaming out of the neighborhoods around them, but some of the even more significant discoveries are not quite as exciting, as you said. It’s like hot gas…

Pamela: Well, yeah, but it’s hot gas jetting out of black holes…

Fraser: Right, or galaxies colliding together…

Pamela: And clusters colliding!

Fraser: Right.

Pamela: One of the coolest discoveries to come out of Chandra, and this is one of the ones that actually in some ways may have sounded the death knell for modified Newtonian dynamics, the alternative to dark matter in theories trying to… well no, it’s not that there’s invisible stuff, it’s that we don’t understand gravity… No, we understand gravity, and we know we understand gravity because the images from Chandra allow us to look at clusters, and the important one here is the Bullet cluster. And when you look at it you can see shocked gas from where the two clusters are starting to collide. But then you can also see these orbs of dark matter imaged via gravitational lensing. So you look very carefully at the images and measure the distortions in the background galaxies and by looking at the distortions you can figure out, well, this was distorted by dark matter, this wasn’t distorted by dark matter. So by combining Chandra which gives us the gas, and by looking at gravitational lensing of background galaxies, we can map dark matter and gas and we can see that the two are segregated… they aren’t together. And this is just a fabulous result… we know dark matter is stuff because of Chandra.

Fraser: Right, and that there are situations where the dark matter can be separated from the galaxy and the gas that’s in the galaxy so that you can actually see it as a separate entity. So that whole idea of not understanding gravity has just gone out the window.

Pamela: And we’ve now seen this in multiple different clusters. In addition to the Bullet cluster we can also see it in the ever-so-poetically-named MACS J0025.4 -1222. And we can also see it in a much more mixed-up way in Bell 520. So all these different systems are showing us evidence of where the dark matter and where the gaseous materials are located by using Chandra to give us the gas content.

Fraser: And I think one of the other things that’s really interesting is when astronomers will use several of the great observatories to do some of their images. So they’ll take an image of the same part of the sky in x-ray and then they’ll merge that with images from Hubble and then they’ll merge that with images from Spitzer and you get almost like three different colors in one image; but it’s not colors, it’s three different wavelengths that are telling you completely different things. So you see the gas with Spitzer, you see the visual stars with Hubble, and then you can see the dense objects or the colliding gas or the hot gas areas thanks to Chandra. And when you have these working together, it tells a much better story.

Pamela: And I know there’s a lot of people out there who don’t like false color, but the combined images of the great observatories scientifically paints such a new and interesting picture… especially when looking at supernovae… where we’re able to see for the first time the neutron stars in the centers, and the gas jets they’re emitting, and the materials around them. That was one of Chandra’s first targets was actually looking at just supernovae and giving us a new view on these well-known objects. What we learned was really, really astonishing. Go out, look at a supernova. Look at it again in the Chandra galaxies. Cas A is another example of these amazing systems where we see so much for the very first time. The Crab Nebula is really my favorite.

Fraser: Yeah, well and I think one interesting one as well is supernova 1987a which was in the Large Magellanic Cloud, and it only happened… what… 25 years ago… right?

Pamela: Yeah.

Fraser: I remember when it happened… it was in the news.

Pamela: Our good friend Phil Plait researched it.

Fraser: Oh really? I didn’t know that! And so we can see it year after year expanding… this shockwave bubble expanding out from where this supernova exploded. And you can see the hot gas… these filaments and knots of hot gas where the supernova is colliding with the nebula that’s around it because the supernova exploded in a star-forming nebula and is now clearing out a lot of space and starting new solar systems and forming them… so you can imagine these knots of gas might be denser pockets… the locations of future solar systems.

Pamela: And there’s some really fabulous things even with much more… in some ways simpler systems… there’s the Cat’s Eye Nebula for instance. Looking at it you can start to see again the high-energy shocked gas and this is a cooler system with a white dwarf. And it really lets you see where are the shocks, and that’s information we didn’t used to have. It makes for much more fascinating images. But, the thing I think a lot of us forget, and so far we’ve managed to forget it for 18 minutes, is Chandra’s also gotten pointed back at the earth. You can use Chandra to start to observe aurora and it can be used to see exactly what’s happening as these high-energy particles from the sun are interacting with our own atmosphere.

Fraser: That’s pretty cool.

Pamela: It’s very, very cool.

Fraser: I know that the x-rays that Chandra gathers are so valuable that they’ll even use the time in between, so when Chandra is slewing from one target to another, it has to sort of go past all this other space and all of that data is actually made available to astronomers as well. As it moves the track is maintained and any x-rays that happen to bounce into its detectors along the way, they’ll use that as well. They’re actually starting to piece together whole sky surveys, thanks to some of the random data that Chandra has gathered.

Pamela: The serendipitous observations….

Fraser: Yeah, I mean with Chandra… especially with x-rays… you really need to focus on one target, wait a long time, and gather all those precious photons at that high energy.

Pamela: Proposals are written for kiloseconds…

Fraser: For kiloseconds… I don’t understand…

Pamela: So you say, “I need 16 kiloseconds on object. That means you need 16 thousand seconds observing something.

Fraser: So… several hours.

Pamela: Right. So for instance when I was observing galaxy clusters with the McDonald Observatory 107-inch, we could get pretty good observations in 900 seconds of fairly distant… admittedly by local standards… so something a couple tenths of a Z away… clusters… 900 seconds, there’s all your galaxies, move on, find your next cluster. But to look at closer objects and end up using sometimes many, many more seconds to get at the x-ray data… you’re literally counting one photon at a time.

Fraser: And so what do you think is the connection between the observatory and Chandrasekhar? Why was it named after him?

Pamela: Well, a lot of the really cool objects that are getting observed with it are the types of things that, well, Chandra’s theories explained why they’re possible and why we should go looking for them. The white dwarf inside of the Cat’s Eye Nebula, the many different neutron stars, the pulsars, all of these objects… he’s the one that predicted these. And then black holes… he’s the person who figured out that well, if this mass gives you neutron stars then this greater mass… oh, oh dear… this collapses even more. These are his objects and these are the objects detected by the Chandra Observatory.

Fraser: And, so the last thing I’d like to talk about is how exactly does Chandra work? Because we’ve talked a bit about x-ray observatories in the past… With a visible light observatory you’ve got a mirror, and photons come in and they’re focused by this mirror and you use a CCD camera to record the image. But I know that x-rays are much higher energy and they’re trickier to get a hold of.

Pamela: Yeah, that would be an understatement.

Fraser: So how does Chandra do that when mirrors don’t work?

Pamela: What they do instead is they have nested cylindrical surfaces, and these nested surfaces slowly, using basically grazing incidence angles, reflect the light… getting it down to the detector. So the light comes in, it reflects off the inner edges, goes to a slightly better angle, gets focused a bit more, until it finally hits the detector.

Fraser: So, it’s like you’re nudging it.

Pamela: You’re nudging it ever so carefully.

Fraser: Right, because there’s no way to actually make them bounce, but you can just change their angle a little bit. So then would you say that we’re not actually… it’s not like we’re focusing a huge area, like you might with say Hubble or a like great big observatory, you’re mostly just getting a little more focus than you would…

Pamela: They actually are able to focus the telescope very, very well, it’s just a different technology. So with Hubble you are going to get tenths of an arc second. But with Chandra you’re still getting half an arc second of resolution, which is better than most ground-based telescopes can get. The telescopes on an average night, not a great night, not a horrible night, but an average night at McDonald we were looking and 1-2 arc seconds of good sky seeing. So here, Chandra is getting better than that, and it’s getting better than that with x-rays. This is one of the profound things about Chandra Observatory is when we first started building x-ray observatories in the ‘70s, you basically pointed and said that giant area of the sky, there’s x-rays there somewhere. There’s been a billion fold increase, literally, in sensitivity and resolution combined that allow Chandra to count individual photons coming off of distant objects and resolve them at the same resolution that you get from the best ground-based telescopes under average conditions.

Fraser: So you said that Chandra will have maybe a 15 year life span, and we’re ten years into it… What’s going to be next? What will replace Chandra? Because this is something that you’ve got to have an x-ray observatory going…

Pamela: So we want Chandra to keep working… it would be awesome, but we do have to plan for the future. And being scientists, we do want to eventually get even better data… we do want to be able to collect more photons in less time and at higher resolutions. So right now there’s a joint mission being planned named the International X-Ray Observatory… it’s a joint mission between the European Space Agency, NASA, and JAXA which is the Japanese space agency. And they’re hoping to launch it around 2020. Now the thing to remember is that everything in NASA is in flux right now, and strangely everything seems to be set for 2020, so expect that date to slide, expect that name to change, expect anything to be possible.

Fraser: Humans landing on the moon… finding Earth-sized planets with their x-ray observatories….

Pamela: Yeah, that one’s not going to happen. But if you put a comma in there, I’ll go with it. Finding Earth-sized planets, finding a better x-ray observatory. Yeah, let’s go with that.

Fraser: So the replacement could go up in 2020.

Pamela: We’re hoping…

Fraser: Right. And it will be more better.

Pamela: Yes.

Fraser: Cool. Alright, well that explains everything. Thanks a lot, Pamela!

Pamela: Well, it’s been my pleasure, Fraser.

Transcript: Chandrasekhar

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Fraser: Astronomy Cast Episode 191 for Monday May 24, 2010, Chandrasekhar. 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. My name is Fraser Cain, I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville. Hi Pamela, how’re you doing?

Pamela: I’m doing well, how are you doing Fraser?

Fraser: I’m doing very well also. And we don’t normally do this, but I wanted to send a special message to Ally who wrote us in… and congratulations on getting a B on your test. So, we’re gunning for you. Right, let us move on to today’s show. So, the first half of the 20th century was a productive time for astronomy, with theorists working out much of the science that we take for granted today. One of these astronomy stars… pardon the pun… was Subrahmanyan Chandrasekhar, who determined the maximum mass of a white dwarf star and won a Nobel Prize. So Pamela, another duo… partnership… the person and the robot. So, today we’re going to talk about the person who was the inspiration for the robot which is actually up there doing work today, so we’ll have a lot to talk about the Chandra mission, but let’s talk about the person.

Pamela: Sounds good… they’re both full of a lot of high energy so it works out.

Fraser: And we were talking about this before… trying to sort of work out how to pronounce his name… now Subramayan, that is…

Pamela: His patronymic….

Fraser: Right, so that’s almost like a last name so it’s…

Pamela: It’s a different way of handling names than we’re used to in the Western language. It’s not your friend-to-friend name first and then your family name or your patronymic second or third, but rather they start with the patronymic and then do the friendly person-to-person. So calling Chandrasekhar “Chandra” is much like calling Elizabeth “Beth.” It’s a nickname for the person’s name.

Fraser: But from here on out, we’re just going to call him Chandrasekhar.

Pamela: Or Chandra.

Fraser: Right… ‘cause we’re close… we’re like that…

Pamela: I’m actually academically sort of descended vaguely in a class by class way to Chandrasekhar…

Fraser: Well I wonder… and unfortunately I don’t know all my history here… there is a number that mathematicians use to determine how many positions they are…

Pamela: The Erdos number…

Fraser: That’s right!

Pamela: I do have an Erdos number… but it has nothing to do with Chandrasekhar. And what’s even cooler is the Bacon-Erdos number, which I challenge all…

Fraser: What’s your number?

Pamela: So it turns out that I actually have a Bacon-Erdos number of 6 which kind of makes me proud… it comes from papers that I worked on with Dr. David Lemberg at McDonald Observatory to get to Erdos and then working with Kevin Grazier on the Universe to get to Bacon… and I’m kind of stupidly proud of my Bacon-Erdos number.

Fraser: Oh, I see, so you’re connected to both Erdos and Kevin Bacon by various degrees of separation, ok… someone should work out something like that for astronomy… what’s your Einstein number? How far away removed are you from Einstein?

Pamela: I’m probably pretty close because of some of the people that I’ve published papers with… I need to figure that out at some point….

Fraser: Anyway… we’re completely off topic… so then it’s time for the history lesson. Who was Chandrasekhar?

Pamela: He was one of the most concentrated scientists… and I didn’t mean for that to be a pun, but he was one of the most focused scientists of the last century. He approached research with an intensity and a passion that has rarely been seen, I think it’s safe to say. His best discovery in terms of “Wow, that changed everything,” may have been the understanding that when large enough stars die, they collapse to the point that the material is so packed together that it can’t get any closer without actually changing states. So when the sun dies… it’s a normal, everyday, not-too-big, not-too-dangerous of a star… when it dies it’s just going to collapse down until the electrons start pushing on each other and the electron degeneracy pressure supports the star as a white dwarf. But if a much larger star… something that might have started its life off as a 6-8 maybe 10 solar mass object, when it dies it leaves behind a core that’s more than 1.4 times the mass of the sun. Something that’s greater than this 1.4 times the mass of the sun, when it collapses down the electrons go no, can’t, can’t handle it anymore… and the electrons and protons actually will end up combining, releasing energy, releasing neutrinos, and the star collapses down into a neutron star. If something is much, much bigger than that, even the neutrons can’t push one another apart and instead you end up with a black hole.

Fraser: Right. And we get the Chandrasekhar limit, is this number which is the maximum mass of a white dwarf star. So if a star somehow happens to gain more mass that pushes it beyond this Chandrasekhar limit… like 1.44 time the mass of the sun… then it’s too much and it just collapses catastrophically and you get a supernova.

Pamela: Now the thing is, he came up with that while on a boat from undergraduate school in India and he graduated college at 19. He came up with his theory while on the boat, at the age of 19 to attend graduate school in Cambridge.

Fraser: Well, now we’re getting ahead of ourselves, so let’s talk about his history then… So, Chandrasekhar… that’s an Indian name.

Pamela: He grew up in Punjab, in British India, which is now Pakistan. He started out speaking Tamil growing up. He comes from a Hindu family, and he actually comes from a scientifically famous family. His uncle was C.V. Raman who came up with the Raman effect which we’ll talk about in a different show. Nonetheless, really cool thing needed to understand the splitting of spectra… and he was a Nobel Laureate. So here we have Chandrasekhar growing up in a family of a prominent physicist. As a child he was home-schooled, his father was an accomplished musician, he worked for the railroads. It was an interesting childhood yet then led to him to attend the Hindi High School and then Presidency college, and like I said, he graduated from college at 19 with his Bachelor’s degree.

Fraser: And then had to go to another country to get an even better education, right?

Pamela: Well, just as it is today, there’s only a few really, really top colleges in the world. At the time, the top college was probably Cambridge… arguably Oxford… maybe Harvard… There’s only a limited number of really top schools you can have in the world. Cambridge was one of them… it remains one of them. And he was able to get to go there for graduate school and then he stayed on with a fellowship after that before going to the University of Chicago. Along the way he got married to another woman from India who was another scientist as well, someone who had actually attended Cambridge with him… was at Trinity College… and one of the neat things in his biography is she actually not only became a stay-at-home wife in a lot of ways, but was in some ways his personal assistant for science… she could read over his papers and offer critiques. So she was there to support him… by just making sure that he ate. If you’re too busy of a scientist, someone usually feeds you. I’m lucky enough that my husband, when I’m working on grants, will feed me.

Fraser: Perfect!

Pamela: But she was there to help him in all aspects of his life.

Fraser: Right. And so you say that he ended up at the University of Chicago?

Pamela: Yes, and he was there throughout the entire rest of his career with the exception of during World War II when he worked on ballistics at the Aberdeen proving ground, instead. But throughout his life he was a very dedicated theorist, although he did have an office at the Yerkes Observatory, and while he was at Yerkes Observatory he was still teaching his classes at the University of Chicago, which was a bit difficult and led to him occasionally making insane drives through snowstorms. There’s one famous anecdote of… anyone who could, attended Chandra’s courses… he was not the kind of researcher who couldn’t teach, though those exist… we wish they didn’t… but it happens. You’re a trained scientist, you’re not a trained teacher. And Chandra was one of the exceptions… a lot like Fermi. He could just teach things amazingly well. And one day, during a particularly bad snowstorm, he was told… just don’t bother. Why are you driving the entire 200-mile round trip between Yerkes and the university to teach this class on stellar atmospheres? Well, the only two students who showed up in class that day were Tsung-Dao Lee and Cheng Ning Yang, who if their names were pronounced correctly would know who I just said… they won a 1957 Nobel Prize in physics. So he made that 200-mile round trip through snow, and it turned out that the people who he took the time to teach, who he put the effort into, both went on to get Nobel Prizes before he did and that’s just kinda cool.

Fraser: So, he was a professor, he had an office at the observatory, but his research… where did his research really start, and what were some of the major advances that he made?

Pamela: Well he started fully involved in stellar structure. This is where he worked on this theory of white dwarfs, where he then went on to study stellar dynamics, and he just migrated through the different physics involved in stars, moving on to the theory of radiative transfer… Eventually he worked on black holes, and in his final years he was working on the new field of gravitational waves. So he always kept himself in highly mathematical fields… if you ever get the chance to read any of his books, they’re very precisely written… no word that isn’t needed is included… but the mathematics doesn’t skip steps. He just goes through and does it right and does it well.

Fraser: And would these be books that your sort of regular person would be able to read, or is there a lot of math in there?

Pamela: It’s solid math. If you were an engineering or science major in college, you might be able to survive this. The thing about stellar atmospheres is it’s beautiful math. This is someone who really doesn’t like doing math… and a lot of relativity has reduced me to either throwing things or crying, but stellar atmospheres is the type of thing that it’s a lot of algebra… you chew through it… there is some integration… you do need to know calculus… but you chew through it meticulously, and you can actually, on paper, build a star. And that’s amazing! But, it’s overwhelming to look at. When I was an undergraduate, I got to take stellar atmospheres from Eugene Capriotti, who had done his PhD work under Chandrasekhar, and I remember the first day of class sitting there… and this was my second year of college… so I’m sitting there at 19 as he spews equations across the chalkboard, and I’m still writing down the top of the third chalkboard as he’s erasing the first chalkboard… and by the end of that class with Eugene Capriotti I had the realization that I knew all the math I needed for the course, and dropping the course was not going to make it easier later, but it was the type of thing that I just had to sit down and consume. It’s not something you can scan-read, it’s not something that you catch onto quickly… you have to chew it up and understand it. But if you have that basic perseverance with algebra and you have that basic perseverance with figuring out the calculus as needed, any of you out there could figure out how to build a star on a notepad or in your computer.

Fraser: Whether you would want to… is another question, but…. So we’ve talked about stellar structure and white dwarfs… but he did a lot of work in stellar dynamics. What is that and how is that different?

Pamela: Well, stellar dynamics is basically the theory of how is it that stars move… that’s where the word “dynamics” comes in… and so you’re looking at the statistical understanding of how is it that globular clusters keep their form whereas open clusters drift apart? How is it that different systems evolve over time? For instance our modern understanding of stellar dynamics allows us to finally understand that globular clusters actually beat like hearts, and for the middle part of Chandra’s career he’s actually looking at the stellar dynamics of our Milky Way galaxy. It’s not sexy work, but it’s fundamental work that really helps us understand how it is that things hold their shape and change over time.

Fraser: Right, and up until some of the recent missions, like the WMAP, this was one of the ways that astronomers would try to get at the age of the universe.

Pamela: Right. It didn’t work, but…

Fraser: No, no… that’s right… but at least you could determine how old they were and how they were changing… So what did he work on next?

Pamela: So the next thing he was looking at was radiative transfer. This is one of the fields of astronomy that is… often when you’re in it, you think you’re taking quantum mechanics. It’s the theory of how is it that light is absorbed and re-emitted by nebulae. It’s the theory of how do we end up with the spectral lines that we see and that we don’t see in stars. All of these different theories—that all falls into radiative transfer.

Fraser: And so… sorry… like I remember when we were talking about stars… is this part of the radiative zone of a star where light is generated in the core and then has to radiate from atom to atom slowly moving its way out through the radiative zone until it can hit the convective zone…

Pamela: And the exact same physics that describes the radiative zone inside of a star is the same physics that applies to light passing through a cool nebula. It’s just different parameters to solve the same type of problem. Now, there are different boundary conditions and sometimes you have to worry about one set of physics while in other cases you have to worry about another set of physics being the dominant player. But it’s the same concepts that play in both cases. And trying to figure out absorption, trying to figure out spectral lines, trying to figure out just how is it that light finally makes it to the surface of the star and makes it from one side of the nebula to another. These are interesting quantum mechanics problems that are difficult and he spent a lot of years of his life looking particularly at different equilibrium states and how it is that things radiate.

Fraser: Right, and when you say equilibrium… like for example, how a star can remain at a certain size where the light pressure pushing out matches the gravity pulling inward?

Pamela: And not just that, but you have heat pouring into a nebula, it’s absorbing some of the wavelengths and reradiating them in all directions, there’s different cascade effects going on, and so at different temperatures you can have nebulae supported in different ways. They’re just externally heated, where stars are internally heated.

Fraser: Right. And this is an incredibly long career… I mean we’re looking at what he did in the 50s, the 60s… I know in the 80s he worked on black holes.

Pamela: He kept doing science up until he died in ’95. This is someone who was born in 1910, was doing Nobel Prize quality work in 1930, and kept on doing cutting edge research until ‘85.

Fraser: And he did get a Nobel Prize in ’83.

Pamela: Yes… he finally got one. And it’s funny, it was in some ways actually a disappointment to him because the Nobel Prize he got… admittedly I just did the exact same thing… looked at his earliest work and praised that. He felt that it somewhat denigrated the work he did later. It’s sort of like saying “You peaked at 19, dude!”

Fraser: Right. Yeah, that would be pretty frustrating.

Pamela: Admittedly, it was his discovery that wasn’t accepted for a long time… and part of the reason that he went to the University of Chicago was to escape the peer pressure to change his theory that he was experiencing at Cambridge. He put up with so much stuff to push forward and to get people to accept that white dwarfs are real, neutron stars are real… well, we knew about white dwarfs… but neutron stars are real, black holes exist. And when that finally was accepted, that changed everything. You get Nobel Prizes when you change everything.

Fraser: And so which of those… was it for the degenerate matter…

Pamela: It was for his work on stellar structures, specifically the Chandrasekhar Limit.

Fraser: Right.

Pamela: It was a shared Nobel Prize as well, so while it was his work that led to the Chandrasekhar Limit, it was all of the work he had done on stellar structure that ended up getting him the shared Nobel Prize.

Fraser: And you said that he passed away in ’95…

Pamela: In ’95. While I was an undergrad, it was really interesting to have him pass away with one of his students there, now as one of our most senior faculty, to talk about him over the years. You got to hear the stories that you only find buried in the backs of biographies. From 1952 to 1971, Chandrasekhar was the editor of the Astrophysical Journal. And this was very much in the defining days of “What’s the difference between Astronomy and Astrophysics?” Chandrasekhar was perhaps one of the first people to work very hard to combine physics and astronomy… there were others… there were Eddington and a whole group of people that he was part of the cadre of that developed this new field. Chandra would set certain periods of his day that were only Astrophysical Journal, and if you tried to interrupt him with science, there was nothing you could do… he would send you away. There were other parts of his day that were strictly dedicated to science and if you tried to ask him about class or the Astrophysical Journal… you’re going to get sent away… and his ability to compartmentalize his life and have absolute focus is part of what made him so good at everything he did. It makes me wonder in our modern day world of email where if I don’t respond to something in 45 minutes I’m getting a phone call… hey did you get my message? Could this type of a scientist do the work he did? It was his ability to say right now, at this point in my life, I’m only going to do stellar structure. Right now I’m only going to do gravitational waves. His ability to segregate his time allowed him to do amazing things in a focused way that I don’t know how you can do in the age of email, and I really respect the ability to focus that he had.

Fraser: You just don’t answer your email.

Pamela: But then the phone rings…

Fraser: Don’t answer the phone…

Pamela: But then the other phone rings…

Fraser: Don’t have another phone…

Pamela: But then they Skype me…

Fraser: Alright, you got me there. Yeah, I remember when we were at the American Astronomical Society there was a big party and you were kinda walking me around and pointing out people like oh, Nobel Prize… oh, Nobel Prize… pointing out these people… and it’s this connection… we have this connection with people who now have done all this amazing work, and yet I think you can go and you can talk to them and you can find out their ideas and you can ask them questions and hear their responses. And that gift that they give of their interest in learning and knowledge and of the universe and then their professors… and that comes out everyday with the people that they’re interacting with. I think that’s what’s really special about the field of academia that you really just don’t get with other “celebrities,” and I’m using “air quotes” when I talk about celebrities. You don’t necessarily have that same connection with a famous actor or musician when you’re working in their field. So I think that’s just a really special thing and it’s amazing that you can attend a class with a Nobel Prize winning physicist, have them teach you about stellar structures, and then go to your other classes. Imagine what impact that would make in your life, so…

Pamela: Well, and some of the Nobel Prizes that we have today have gone to some of the most giving people. John Mather is someone who I’ve seen very graciously talk to all sorts of people, answering their questions, taking on new technologies to give talks in Second Life, talking with undergrads at AAS meetings… another one is Barry Blumberg who admittedly got his Nobel Prize in medicine, but we’ll accept him anyways, and he loves astronomy and he’s now working with a lot of the moon projects coming out of Nasa Lunar Science Institute and is tangentially related to our Moon Zoo project that is coming out of the Zooniverse. A whole bunch of my students met him and they had no clue who he was. He was just this friendly older man… well-dressed… but looked like a professor, just another professor, and he walked down the row and talked to each of them about their posters… and it was like yeah, we met an old guy. One of my students I had to like kick because he was talking to a pretty female graduate student, and there was this old guy trying to ask him questions… and who do you give priority to? And after the meeting… it just failed to occur to me that I needed to point out to my students that they had a Nobel Prize winner talking to them because in the moment I knew better, but I should’ve told them after and forgot to.

Fraser: Right.

Pamela: And one of my colleagues was like “oh my god I just met Barry Blumberg!” And one of them Twittered “oh my god that’s so cool!” To which I got to respond, “Yes, and he talked to you as well.” He’s just a down to earth guy and no one realized… it was awesome.

Fraser: Alright…. well, we kinda went a little off of topic in the end there so….

Pamela: We apologize for the random mutterings… this is what happens when we talk about people…

Fraser: Yeah, I know… I know… you get all these anecdotes. So again, next week, we’re going to talk about the mission. It’s a wonderful mission, one of the most productive missions that has happened in recent times. So, I’m looking forward to that. We’ll talk to you next week Pamela.

Pamela: Sounds good, Fraser. I’ll talk to you later.