Astronomers Find a 'Hole' in the Universe Scientists have found a space nearly a billion light-years across that contains nothing — no stars, gas, galaxies, or mysterious dark matter that astronomers believe makes up much of the universe. The scientists who performed the study explain what it might mean to find... nothing.
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Astronomers Find a 'Hole' in the Universe

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Astronomers Find a 'Hole' in the Universe

Astronomers Find a 'Hole' in the Universe

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  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
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You're listening to TALK OF THE NATION: SCIENCE FRIDAY. I'm Ira Flatow.

And for the rest of the hour, this hour, a space mystery. Bring up that spooky music. A giant hole in the universe. Scientists studying several different maps of space have found a space in space. A space nearly a billion light years across that contains nothing - no stars, no gas, galaxies, not even any of that mysterious dark matter that astronomers believe make up a lot of the universe. It's even colder than expected there, and there are fewer radio emissions. So what does it all mean?

My guests joining me now are Larry Rudnick, distinguished teaching professor at the Department of Astronomy, University of Minnesota in Minneapolis, and Liliya Williams, associate professor in the Department of Astronomy there. They're two of the authors of a paper on the area of space that's been submitted to the Astrophysical Journal. Welcome to the program.

Dr LAWRENCE RUDNICK (Astronomy, University of Minnesota): Thank you. Good to be here.

FLATOW: Larry, it's been a few years.

Dr. RUDNICK: It has. You're looking good, Ira.

(Soundbite of laughter)

FLATOW: Yeah. Larry and I used to work together a lot on Newton's Apple back 25 years ago or something like that.

Dr. RUDNICK: Right. Right.

FLATOW: That's a long time ago. Tell me, Larry, why is this so mysterious? Why, you know, did you just discover it now?

Dr. RUDNICK: Well, just discovering it now was a complete accident. I was frustrated one day with another project that I was working on, and we have a very strong cosmology group here at Minnesota, and we had had lectures on this funny cold spot in the cosmic microwave background from the very early universe. And I and my grad student, Shea Brown, have been working on another survey of radio galaxies called the NVSS survey, and so I thought, well, I can't get my - the stuff I'm working on to work, so I'm going to just go look at that survey in the direction of the cold spot, and I found that there were way too few galaxies there, and that was the beginning of it.

And what actually happened at that point was I was completely confused about what I was looking at. So I called Shea in, and I said, look at this, what's going on here? And he said, oh, well, that's the integrated Sachs-Wolfe effect. And I said, what are you talking about? And so he explained that they had just done that in their - studied that in their in cosmology class, and that's what we were looking at, and that was the beginning of knowing that we were looking at a big void. And we just marched ourselves down to Liliya's office and told her she had to help us out and figure out what this thing was.

FLATOW: Liliya, do you have any guesses on what's going on out there?

Dr. LILIYA WILLIAMS (Department of Astronomy, University of Minnesota): Yeah. What - it appears to be something that we have expected to see, but haven't seen in that setting. So we know that in the universe, which is dominated by dark energy, we would expect to see areas in the universe that are particularly empty to also be colder than usual. And areas in the universe that are - that have more than their fair share of matter to be somewhat warmer. So people have predicted this for a long time, and people have been observing this in sort of in a stastical sense. So what we have discovered is a specific instance of this happening in a very localized region in the universe.

FLATOW: 1-800-989-8255 is our number. Talking about this - it's a billion light years, Larry, across?

Dr. RUDNICK: Yeah. And that's - that was the surprise part. So as Liliya said, the physics of it was expected and already had been seen. But what we did for the first time was isolate a single region, and the calculations Liliya did show that this region was just enormous. The size of this void itself was just way beyond what we expected.

FLATOW: So that's a good chunk of the universe, isn't it? I mean, what percentage of the universe would that billion light years be?

Dr. WILLIAMS: Oh, no, it's still not a very big chunk of the universe.

Well, it depends what you mean. It's one of the biggest structures, if not the biggest structures we know of, but it's not comparable to the size of the universe. It doesn't take up like half or even one-tenth of the universe. No, it's not that big.

FLATOW: Mm-hmm.

Dr. RUDNICK: But another way to look at that, though, is what will it look like on the sky if you could actually see it.

FLATOW: Right.

Dr. RUDNICK: And it would cover an area of the order of about 44 moons or so. So it would be enormous if you could see it. But still, as Liliya says, it's still a tiny fraction of the volume of the universe, which may itself be infinite. But this is - it was a surprisingly large chunk, but small in the very grand scheme of things.

FLATOW: Lawrence, you have not lost your talent for explaining things to the lay audience.

Dr. RUDNICK: Thanks.

(Soundbite of laughter)

Dr. RUDNICK: Under your tutelage.

(Soundbite of laughter)

FLATOW: Thank you. Could you think, Lawrence - Larry, you think you could find more of this? I mean, if the theory predicts them, there should be more of them, right?

Dr. RUDNICK: I'm going to let Liliya try that one.

FLATOW: Liliya?

Dr. WILLIAMS: Well, we don't know yet. The current prediction for what we expect to find in the universe, in terms of large voids, are probably saying that we shouldn't find something that big. But that's not the final conclusion. So we don't really know at this point. We are - what we have found gives us a wonderful opportunity to start looking for other voids like that. But I don't really know the - nobody knows the answer to your question right now, whether we should expect to see more of these or not.

FLATOW: Mm-hmm.

Dr. RUDNICK: And I think that's probably why it's exciting. We have sort of opened up a new regime. People have studied voids on much, much smaller scales before. And there were lots of them, and people are starting to do detailed studies. But, as Liliya was pointing out, there could be a whole population of these things out there to find, and we may have just found the tip of the iceberg. People didn't expect to see it from the little - the smaller things that they looked at before. But we just don't know.

FLATOW: Isn't the universe supposed to be made of 20 percent about - this dark matter or more? When do we expect even to see that there?

Dr. WILLIAMS: No. Apparently, that void is empty of dark matter. It still has dark energy in it, or so we think. But there are no stars, no planets, no gas and no dark matter.

Dr. RUDNICK: And the lack of - yeah. And the lack of dark matter, I think, is -we can't see the dark matter. So it's not that we don't see it that's the basis of the claim that we're making. The point is that in order to create this cold spot in the microwave background, we have to pull out the dark matters up also. So it's really an inference from our observations that the dark matter must be missing from there.

FLATOW: Mm-hmm. Now, you've been an astronomer for many years. I'm interested in the process that goes on here. Why suddenly you find something that you hadn't seen before? What goes on? You know? How did you make a discovery like that? Is there a light bulb? Is there a moment? What's - give me an idea of the processes as a scientist.

Dr. RUDNICK: Well, there was a moment. I mean, there are projects - you know, as a scientist and as an astronomer, most projects are very long-term. You get an idea, something that you want to do. You maybe do a little pilot study or something to see whether it's feasible. If you need resources to do it, then you have to write a proposal. You may end up waiting a year. You may get turned down. You may need telescope time. You right a proposal for that. You may get turned down on the big telescopes. Now, the ratios are often ten to one rejection, and then that most proposals don't get on.

And so most of the time, in order to do a significant project, there's a lot of planning, and a lot of time that goes in. And this followed absolutely none of those rules because it was just an accident. And I think it's because we were so prepared in terms of already thinking about the physics, thinking about the interesting issues that, when it came up, it was, oh, my gosh, this is something exciting because we had all the background to recognize it. But it involved none of the planning that you normally do.

FLATOW: Yeah, a Louis Pasteur moment.

Dr. RUDNICK: Absolutely.

FLATOW: 1-800-989-8255. Let's go to Tim(ph) in Grand Rapids. Hi. Tim.

TIM (Caller): Hi. It's a pleasure to be on your show. I'm a big fan. I know that there are some surveys looking for symmetry because the universe - it's a big question on whether it repeats itself or whether it's, you know, boundless and of limited space. But will this large void be helpful in looking for symmetry in the universe?

Dr. WILLIAMS: Well, no. We don't think that there is any symmetry in the universe besides the fact that the universe is uniform and looks the same in all directions at any given time. So, for example, we don't think that there are repeating universes. So, in that sense, we don't think there is symmetry.

Dr. RUDNICK: It's an interesting idea. But right now, it just doesn't - it doesn't look like there's anything there.

On the other hand, we still do have some other puzzles that are coming out of the cosmic microwave background. There's a so-called axis of evil, which half of our colleagues are going to get angry that we even mentioned it because they don't think it's a real thing, and the other half saying, oh, good. They acknowledged that there is a problem out there.

We have some really interesting problems with symmetries within the universe that we see. These are not the symmetries that the caller is asking about between multiple universes, but symmetries within our own universe that's still are quite puzzling.

FLATOW: Tell us about the axis of evil.

Dr. RUDNICK: Oh, you - I shouldn't have gone there.

FLATOW: Come on.

Dr. RUDNICK: Liliya will help you.

FLATOW: I can't let you get away with that. You can't bring it up and say I can't tell you about it.

Dr. WILLIAMS: Well, astronomers have a knack of naming things after - with some flashy name that already exists out there.

FLATOW: We know where that comes from.

Dr. WILLIAMS: You know where that comes from. Okay. So what axis of evil in cosmological setting is this. We observe microwaves coming from very, very early universe. And these microwaves are seen in the entire sky. So wherever you look in any direction you see these microwaves. And they form a pattern. It's a very subtle pattern. So the temperature in microwave is almost uniform but there are some fluctuations. And if you look at the global symmetries in your sky, in the observer's sky, in these patterns of fluctuations in temperature, then you see certain symmetries on very large scales. So, for example, something like if you look in one direction, the temperature at 90 degrees from that direction will be correlated or similar to the one just in front of you.

FLATOW: Mm-hmm.

Dr. RUDNICK: It's sort of like a cloverleaf pattern.

Dr. WILLIAMS: Sort of like a cloverleaf pattern on the sky, spread over the entire sky.

FLATOW: Mm-hmm.

Dr. WILLIAMS: So, yes. So, large scale of patterns like that seemed to be aligned with each other. And that's where axis of evil comes from.

FLATOW: I mean, is that - it's called axis of evil because you don't understand why that is?

Dr. WILLIAMS: We don't understand what it is and it is an axis.

FLATOW: Right.

(Soundbite of laughter)

Dr. RUDNICK: Yes. And that's why it's evil - because we don't understand it.

FLATOW: That's never stopped you before from…

Dr. RUDNICK: It's only a temporary roadblock. I'm sure we'll figure it out.

FLATOW: Well, let see - you know, what's amazing about the universe is that, you know, we say this about a lot of things, but I think it's true more of astronomy and astrophysics is…

Dr. RUDNICK: That was close…

FLATOW: I know. It's getting to sound like it. Is that the more we really know, the less we really understand?

Dr. WILLIAMS: No. I wouldn't say so. I would say that, at least from my point of view, the global picture is there. And it really hangs together very beautifully. But the details or certain spots - many spots in our understanding of the universe as a whole are very fuzzy. Some of them are completely missing and sometimes when we do fill them in, they don't seem to match what we already know. But it doesn't - none of these things are a fatal flaw to the global picture of the universe as we see it right now, as we understand it right now.

FLATOW: Mm-hmm. Talking about cosmology this hour, TALK OF THE NATION: SCIENCE FRIDAY from NPR News.

Talking with Larry Rudnick and Liliya Williams, both of the Department of Astronomy at the University of Minnesota in Minneapolis.

Let me see if I can get a quick question in. Let's go to the phones. Let's go to Kevin(ph) in San Jose. Hi, Kevin.

KEVIN (Caller): Hi, Ira. Love the show. Thanks for letting me on.

Hey, the question I have - I guess I more likely know the answer is - is this visible through an amateur telescope?

Dr. WILLIAMS: No. Sorry.

(Soundbite of laughter)

KEVIN: Oh, well.

FLATOW: He knew the answer already.

Dr. RUDNICK: But you can look in the direction and you can just think about it. I mean, so much of what we study in astronomy and the things that we get out of the professional telescopes aren't accessible to the amateur. But look southwest of Orion, look in the direction of the constellation of Eridanus, and you will be facing and can commune with the great void. It's there. But you're just going to have to trust us on it.

KEVIN: I got to wake up pretty early in the morning for that one. Thank you very much, and I really appreciate your reply.

FLATOW: Thanks, Kevin. Does it have a name like that, Larry? Is it the great void or did you give it the name?

Dr. RUDNICK: It has no name yet. We'll see what happens. The first thing it has to do is it has to hold up to scrutiny. You know, we've put our paper out there and there are lots of potential criticisms. We've sort of given it the best shot that we can. But the job of the community now is to try to shoot it down. And shows like this are going to give them even more incentives to try to shoot it down. And so I think the first thing to do is to see whether this idea really survives or not. Are there alternative explanations that would explain the observations and not require a giant void like this? We'll see. And I think that after it becomes established, then if the community decides it needs a name, it'll come.

FLATOW: So far, is the best explanation for this a statistical one? That there's just going to be one of these every now and then?

Dr. WILLIAMS: No. We don't know yet. I mean, this particular spot is definitely exceptional in the sense that it corresponds to the coldest spot in the entire sky of this microwave radiation. And it is also the emptiest region in radio sources, in radio emission that Larry studies. So it's definitely a very interesting spot in our sky. But whether there are other ones like that, probably not quite like that, but maybe there's a host of them that are somewhat not quite as big.

FLATOW: So it's cold and empty?

Dr. WILLIAMS: Yes. It's cold and empty.


Dr. RUDNICK: Boring to travel through.

FLATOW: But nature abhors a vacuum, we've been told.

Dr. RUDNICK: Well, that's an interesting idea. And a lot of people have sort of asked that question of us recently. Yes, if you had a gas like the atmosphere of the Earth and you try to push all the gas into one corner of a room, for example, nature would abhor that vacuum you were trying to create, and it would push the gas back into fill up the room again. But that's not what's going on out in space. There is no pressure like that. And so what's actually happening is that gravitation is causing things to clump so that little pockets that are a little bit denser will pull more stuff towards them and build up bigger concentrations of matter, which will pull more matter in. And they will leave behind empty areas.

And in fact, that's partly why this discovery is so exciting. Because that development of structure in the universe, where the universe started out very uniform and eventually contains planets and stars and galaxies and us, that development of structure is the story of how we got here. And our discovery says, well, maybe we don't quite understand how that structure developed or our theories may not be quite good enough because they didn't predict that we were actually going to see something this large. The physical effect is there - we knew about, but not that we would find something this large. So the question is - do we really understand how structures developed? And we'll see.

FLATOW: Something to contemplate this holiday weekend. Some good fodder for thought. Thank you, Lawrence.

Dr. RUDNICK: Quite welcome.

FLATOW: Thank you very much, Liliya.

Dr. WILLIAMS: Thank you.

FLATOW: Lawrence Rudnick is a distinguished teaching professor, and Liliya Williams is associate professor, both in the Department of Astronomy, University of Minnesota in Minneapolis. Have a good weekend.

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