Colossal Quasar Clump Too Huge To Exist, In Theory
FLORA LICHTMAN, HOST:
This is SCIENCE FRIDAY. I'm Flora Lichtman. We all rely on the sun to survive. It's a pretty big deal to us earthlings. But in the big picture, the sun is just one of hundreds of billions of stars in the Milky Way galaxy. And while the Milky Way is an awesome place to live - I mean, it is, right - it, too, is just one of hundreds of billions of galaxies in the universe. You feeling small yet? I am. There's lots of stuff in the cosmos bigger than us. And now researchers have discovered the biggest thing so far: a glob of galaxies that's four billion light years wide.
That's like stacking 40,000 Milky Ways end-to-end. There's just one problem with this colossal formation: According to cosmologists' calculations, it's not supposed to exist. It's too big. Of course, the universe doesn't play by our rules. So what do we make of this? Could the universe be a little stranger than we thought? Always, right? My guests are here to talk about that and other astronomy discoveries for the rest of the hour. Ron Cowen is a freelance astronomy and physics reporter based in Silver Spring, Maryland. You can read his stories at roncowen.com. He joins us from NPR in Washington. Welcome back to SCIENCE FRIDAY, Ron.
RON COWEN: Thanks a lot.
LICHTMAN: Gerard Williger is an associate professor in the Department of Physics and Astronomy at the University of Louisville in Kentucky. He joins us from Louisville Public Radio. Welcome to SCIENCE FRIDAY, Dr. Williger.
DR. GERARD WILLIGER: Thanks for inviting me on.
LICHTMAN: Let's start with you, Dr. Williger. Tell us a little bit about this, a little bit more about this clump of galaxies. What was it, exactly? What is it?
WILLIGER: It's a large quasar group. And that begs the question: What is a quasar? A quasar is actually a piece of the galaxy. It's the core of the galaxy, which is very, very bright. It outshines the rest of the galaxy by a lot. So it would be like having - if you have a galaxy which is, say, a bunch of houses in a housing development, the quasar's a skyscraper. So it completely outshines - in terms of light - the stuff around it. And if you look at it from far away, it looks like a little point.
WILLIGER: Now, these quasars are a very rare phenomenon. They might be only a fraction of a percent of all galaxies would have one of these bright quasars in them at any one time. They're also transient phenomenon. So imagine you have a skyscraper and it has a light to warn airplanes, but it's only on for a little bit of the time. So what we found is basically a long string of these quasars. They're galaxies. They probably have other galaxies around them. They're faint, and we don't see them yet because we have to stare for a long time.
WILLIGER: And we see this long string of these rare objects which are only bright for a short time, and they're statistically different from the other quasars around in the sky. So it's like finding an archipelago of islands all together, but these islands are constantly bobbing up and down into the waves or all the skyscrapers are turning on their lights at the same time. And we don't know whether that means that there are a lot of galaxies around there - which, well, there's some indirect evidence that there may be - or they all happen to be turning on their lights at the same time. Whichever the reason, it's a bigger cohesive unit than we think should exist based on our best models of the universe so far.
LICHTMAN: Gerald Williger, so tell us about how it breaks the theory. Wasn't this related to something that Einstein put forward for his theory of relativity, that the universe is more uniform than this?
WILLIGER: Well, what Einstein did, he postulated something called the cosmological principle, which says that if you look on a big enough scale, one part of the universe should be pretty much another part of the universe. And that makes it possible for us to take a sample, look at a piece of the sky and say, OK, we're going to learn about the rest of the universe. As long as you look at a big enough piece of sky, you're fine. It's like if you're looking at a map of - or if you're looking at the Earth, looking at, say, the United States from space and you want to know what's in the country, you're looking with your satellite, if you have a little camera with a little field of view and you have, say, a 10-mile swath, then you can only catch maybe a cornfield or maybe a city or maybe Manhattan. But you have to look at enough of that to make a generalization about the U.S.
WILLIGER: And for the same reason, you have to look at a big enough piece of space to understand the universe as a whole, and that underpins a lot of the way - or calculations and the way we look at the universe. So looking at pieces of the sky is actually pretty expensive in terms of telescope time. You have to take a telescope, and you have to look, look and look and look and look. The sky is big.
We can't survey the sky, the whole sky, to the kind detail we want. So we pick a little piece and we study it - fine. And we've made a large number of surveys of various sensitivities in various areas. And occasionally, we look all over the sky.
So in terms of the size of this group of quasars compared the size of the universe, it takes up a volume, which is something like two percent, 140th, 150th of the universe. That's actually really, really big. And so if we want to have a good idea what the universe is like in general, if this is a cohesive unit which is the kind of size is something that you have to probe to get a good idea of the universe, then we have to make our surveys bigger.
LICHTMAN: Hmm. Ron, what do you make of this study?
COWEN: Well, I guess one question I have is, was there enough time since the universe formed for such a large structure to come into being? I mean, is there enough time for that?
WILLIGER: Aha. That's actually the key. Although this is a big discovery, we have to go into the details, and there are several ways of looking at what's an object. OK. You look at our solar system, that's it. It's a cohesive unit. You have the planets. It's going around the sun. It's held together by gravity. You have our galaxy. That's actually also a cohesive unit. You have the stars that are held together by their gravity, and they're spinning around at the center. That's fine. We actually live in a group of galaxies, and that's a cohesive unit too. It's called the Local Group and they're bound together by their gravity.
Now when you talk about clusters of galaxies, those also are bound together by their gravity. But beyond that, there are things called superclusters. Clusters of galaxies tend to be globbly(ph). Superclusters tend to have some complicated structure - snaky, maybe like a skeleton, something like that. They're not round blobs, and they're also less and less and less held together by their own gravity.
Now this large quasar group is big enough. It is - it would be very difficult to accept it being held together by its own gravity. What it could be is a signature of a primordial density fluctuation. When the universe was young, after the Big Bang, there were little regions of the universe that were slightly denser than other regions, and these grow because gravity is a one-way force. You fall in. But it does take time for assemblies of objects to come together by gravity.
This large quasar group is bigger that than that scale. So it didn't pull itself together by gravity. It's just there. Now is it there because there was a big dense spot in the universe when it was young, or do we see this because all the quasars happen to turn on at the same time and otherwise, it's not a lot of extra matter there?
LICHTMAN: Hmm, yet to be determined, I take it.
WILLIGER: Mm-hmm. Maybe they are making a giant Christmas celebration. They're putting up strobe lights in all the skyscrapers.
LICHTMAN: Ron, you were at the meeting of the American Astronomical Society last week in California, and you reported on a fascinating story about an old timer, the oldest star we've ever discovered. Is that right?
COWEN: Right. Right. It's sort for the Methuselah of stars, and it's at least 13.2 billion years. I mean, the way they - ancient as they say, it's 13.9 billion years, give or take, 700 million, and that may sound like a somewhat imprecise number, but it's the most precise number so far. And the thing is that the universe itself, we believe from other data, is 13.7 billion years. So this star formed really early.
And what's interesting is we - as old as it is, it is not the first generation star to form. It's got to be in the second. And the reason we know that is that the first generation of stars formed from the stuff that was forged in the Big Bang, which was mostly hydrogen helium. This star contains some known elements that are heavier than helium, and those would have had to have been forged within the first generation of stars. So it's a second generation star despite the fact that it's 13.2 billion years. And that means the first generation, not only did it have to - we already believed that it lived and died quickly, but that there was some kind of lag, delay between the first generation and the second, but there wasn't much. The delay was very short. That second generation came to into being very, very quickly.
LICHTMAN: Is aging stars - does that come down to just looking at what they're made of?
COWEN: Only it will - there's a couple of ways to do it. People knew for a couple of decades this particular star was elderly because it did - it only had - I'll call it trace amounts of elements heavier than helium. But the way these guys did is they used some star trackers on the Hubble Space Telescope to get a really precise distance for this star, found out that it was 190 light-years from the solar system, which is actually really, essentially in our backyard. And from there, they could get the true brightness of the star and seed it into models where, given the true brightness of the star and kind of the phase of where it is in this evolution, they could figure out exactly how old it was. But in this case, a key was getting its distance. And they looked over a period, I think, of between 2003 to 2011 with Hubble, to get the distance with these star trackers.
LICHTMAN: What are the chances of finding one of those first generation stars?
COWEN: Right. I think we probably can't find it with an existing telescope, but the James Webb Space Telescope, which is Hubble's successor, which is supposed to be launched in 2018, it looked with this infrared eye and it will have the ability to see if not single first stars, certainly groups of the first stars. Looked back far enough in time, 13.7 billion years, and actually have perhaps images of at least groups of these first stars.
LICHTMAN: Gerry Williger, anything to add?
WILLIGER: That's one of the name pushes actually for the James Webb Space Telescope. This very first generation of stars is actually - it's very interesting because the physics changes the actual recipe for how do stars shine - how do they born, how do they shine and how do they die. It's different because these trace elements, although, not a very high percentage, these elements are very, very important because they had a lot of electrons into the mix. And electrons make things happen with photons. And so the whole mechanism how these early stars formed is different from what we know. There are lots and lots of models. We would love to observe some of these so we can see whether the multiples are actually correct.
LICHTMAN: What are some of the - let me just sneak in an ID. I'm Flora Lichtman and this is SCIENCE FRIDAY from NPR.
So what are some of the ideas about how these stars might behave differently, these first generation stars?
WILLIGER: They could be very massive and very short-lived. And - actually, there's a big industry in astronomy, how do stars form, the exact mechanism. You have cloud of gas and then there's a little density clumped inside of it, and then that starts to grow. Gravity is a one way force. A galaxy forms from little density clump (unintelligible). A star, too, actually forms in a very much smaller scale. And so this - you have a collapse and it happens on a certain time scale and then you have an object in the middle, which is getting denser and denser.
And if you push on something in general, you heat it up. So it heats up in a certain way, a certain speed and then eventually forms of jets because there's material crashing in, but not all of it can go down the drain. It's like pouring a bucket of water down a bathtub drain. And the drain can only take so much water and the rest of it splashes back. And then the star will ignite its nuclear fire. It'll turn hydrogen into helium in its core. And then, eventually, if it's a big star, it explodes. And then it feeds the rest of the space around it with elements not only that it made during its life, but elements that were made in the explosion. Those are heavy elements. Now, how many of these heavy elements are made? That's the stuff for the next generation of stars. So we're looking at how the second generation of stars formed, as well.
LICHTMAN: Ron, another story you reported, the incredible number of planets in the Milky Way, new research into this. Tell us about it.
COWEN: Right. And so this is - it's - looking at data from the Kepler space telescope, and Kepler finds planets in a - it's in a pretty narrow patch of sky and it's also pretty distant. And the way Kepler looks for planets is that if planets are aligned very well, they will pass in front of their parent star, periodically, as they orbit as seen by Kepler. And there'll be a tiny, tiny amount of dimming, a mini eclipse each time it passes in front. And that's how Kepler sees planets. And so researchers, for example, looked at stars - the number of planets around stars called M-dwarfs. M-dwarfs are less massive than the sun. They are fainter. They're cooler.
And the neat thing M-dwarfs is they account for 75 percent of all the stars in our galaxy. And people extrapolated from seeing how many planets there were around M-dwarfs in this now patch of sky that Kepler's seen. Basically, it's sort of like one planet per star. And because we think there is around 100 billion stars in our whole galaxy, therefore, there's about 100 billion planets. One thing that's interesting is that another group - David Charbonneau and Courtney Dressing of Harvard - took that a bit further. They wanted to find out the number of habitable - potentially, habitable planets around M-dwarfs.
These are - one way and by potentially habitable, during a zone where water - liquid water could exist on a rocky surface of a planet. And they calculate from the number of potentially habitable planets for any M-dwarfs that Kepler sees that there should be an Earth-size potentially habitable planet within 20 light-years of the solar system. So it would be - there'd be a planet just like home - not orbiting a sun-like star, orbiting an M-dwarf, but basically among the nearest stars in the Milky Way.
And that six percent of the 100 billion number that I just talked about, six percent of them, which is still a very big number, are likely to have planets where liquid water could exist. And, I mean, the whole thing here is that it takes a full year for a habitable Earth-like planet to orbit a sun-like star because the Earth takes a year to form - to go around the sun. So Kepler doesn't know how many Earth-size habitable planets orbit sun-like stars, but they do with M-dwarfs.
LICHTMAN: Well, it's fascinating. Unfortunately, that flew by. But we have to leave it here. Thank you both for joining me.
WILLIGER: Thank you very much.
COWEN: My pleasure
LICHTMAN: Ron Cowen is a freelance astronomy and physics reporter based in Silver Spring, Maryland. You can read his stories at roncowen.com and Gerard Williger is an associate professor in the Department of Physics and Astronomy at the University of Louisville in Kentucky. Transcript provided by NPR, Copyright NPR.