IRA FLATOW, host.
This is Talk of the Nation's Science Friday, I'm Ira Flatow. A little bit later in the hour, a commercial rocket launch, the first of its kind into orbit, and also why people believe weird things. We have a different reason than you think. But first, what makes up a galaxy?
Well, you got lots of stars, probably some planets, a bunch of dark matter and energy floating in space between the stars, you got a helping of gas, and turns out that there's also now a magnetic field that helps make up a swirling galaxy, and that field might help determine how the galaxy formed, or whether there even is a galaxy with more or fewer stars than usual.
Writing this week in the journal, "Nature," a team of scientists report that they have been able to measure the strength of that magnetic field in a far, distant galaxy, looking billions of years back in time, to when the galaxy was only around four billion years old. And when they measure the field, they were in for a surprise.
It turned out to be about ten times what they were expecting. Joining me now to talk about that finding, and why it's significant, is one of the astronomers on that project. Arthur Wolfe is professor in the Department of Physics and the Center for Astrophysics and Space Sciences at the University of California, San Diego. Welcome to Science Friday.
Dr. ARTHUR WOLFE (Department of Physics, Center for Astrophysics and Space Sciences, University of California, San Diego): Thank you, Ira. Pleasure to be here.
FLATOW: Let's talk about the looking at magnetic fields in distant galaxies, it seems like kind of like of an esoteric thing for astronomers to do.
Dr. WOLFE: Well, not exactly Ira. Astronomers had been doing this for years in our galaxy, in the Milky Way that we live in.
Dr. WOLFE: We've know about magnetic fields for a long time. They - we know they exist in stars and planets. And also in the gas in between planets, and using various techniques, we've found that the magnetic-field, interstellar gas in the Milky Way is dynamically significant. It affects the motions of interstellar clouds, and also affects the rate at which stars form, because the pressure exerted by the magnetic field can prevent the collapse of a gas cloud, when it wants to go on its way to make a star.
FLATOW: Hmm. And by looking at these very, I guess, old or young, depending on how you look at them, it's something that's happened when the galaxy was about four billion years old, helps you do what?
Dr. WOLFE: Well, it helps us to understand how these magnetic fields originate, that's been a question for a very long time. The leading theory is the so-called Mean Field Dynamo Theory, in which the rotation of the galaxy winds up magnetic fields, and amplifies, and there's a function of time.
And the time that it takes in a magnetic field to increase by a factor of a few, is about one rotation period of a galaxy which is about two hundred million years. So it takes a long time. But the bottom-line is as we looked back in time, we expect magnetic fields to be weaker in the past, as a major prediction of the dynamo theory.
FLATOW: Mm-hm. So when you'll find this young galaxy to be ten time - half ten times as much magnetic field power as you thought it would be. That sort of upset the apple cart a bit.
Dr. WOLFE: Yeah, we were surprised that they've honestly never expected to detect something like this. And we looked at it for a long time and there it was. It's a big surprise, and we're trying to understand why it is that this magnetic field is so strong.
FLATOW: Mm-hm. Do you have any about this?
Dr. WOLFE: Yeah, we have two right now. One is, that we're looking not at a typical location in this distant galaxy, but toward it center. We know in some nearby galaxies that they have strong magnetic fields at their centers.
Dr. WOLFE: And so that's one possibility that we're looking through the central region of this galaxy. This is important also, because in the centers of galaxies, the densities of stars is very large, and that's very important for us, because the magnetic pressure of this field that we looked at, is so great that it is greater than the weight of the gas above it. However, if you add stars into that next - the gravity of the stars increases the weight of gas (unintelligible) imbalance the field, and exist in an equilibrium.
Dr. WOLFE: So, this is one possibility, that we're looking through the center of a galaxy. Another possibility that was suggested by my colleague, Frank Shoe(ph), who's an expert on this, is that we're not looking at one galaxy, we're looking at two galaxies in collision. And the benefit of that idea is that these galaxies start out with a mild field, the type of field we see today.
Dr. WOLFE: I can use these units, five microgals, and what happens is that when the galaxies collide, a shockwave gets send out, and the shock wave - it increases the density of the gas, but it also amplifies the strength of the field...
Dr. WOLFE: To its current strength, which we think is about a 100 microgals. So, that's one benefit of that model.
FLATOW: Mm-hm. Any - to the late(ph) people, any possibility that the mysterious dark energy or dark matter may play some role in upsetting this idea?
Dr. WOLFE: I don't think so. What we're looking at is not dark matter, we're looking at - we see this magnetic field in ordinary gas...
Dr. WOLFE: And ordinary matter, and so the influence of dark energy and dark matter - I mean dark matter will play a role in terms of the total gravitational field of the galaxy and how the galaxy rotates. Dark energy, I don't think, would play much of a role in this. We just - we're looking at neutral hydrogen, the way - should I tell you how we found this field?
Dr. WOLFE: OK, we use this technique which my other colleague, Carl Hidless(ph), at Berkeley has basically been a leading expert in a number years. It's called Zaman splitting. So let me tell you how this works.
What we do is we see the gas in this very distant galaxy, against the very bright light or bright electromagnetic radio waves emitted by a more distant background quasar. How it happens is, as that radiation from the distant quasar comes through the gas, the gas leaves an imprint on that light.
And the imprint it leaves is what's called a 21-centimeter absorption line. Let me explain what I mean by that. Quantum mechanics tells us that atoms, in this case hydrogen atoms, exist in discreet energy levels. And in this case, if we go from an upper energy level to a lower energy level, a quantum of radiation is emitted in photons, just go over photon. Or conversely, if I add a photon to the system, I can go from a lower energy level to a higher energy level. So, that's what we've seen, is the light from this distant quasar comes by through this gas.
Some of this light is absorbed, going from one energy level to another. And the imprint that's left is a 21-centimeter absorption line. This is known a long time ago, this...
Dr. WOLFE: That's the wavelength of a photon...
Dr. WOLFE: That's absorbed. Now, when I turn on a magnetic field, the magnetic field changes the energy of this atom, because atoms are like little, dipole magnets.
And what was once the upper energy level, which at one time was one level, now splits into two levels. And what we've done is measured the splitting. In other words, instead of the 21-centimeter line being one line, its splits up into two lines.
One with a wavelength slightly less than 21-centimeters, one with a wavelength slightly greater. And using the hundred-meter telescope at Green Bank's Radio Telescope, this is the largest, steerable telescope in the world. It's really a magnificent machine. After spending many, many hours looking at this object, we were able to see the splitting and the magnitude of the splitting tells us how strong the magnetic field is. I hope I've made sense.
(Soundbite of laughter)
FLATOW: Well, I get - but the take home message is you've found a magnetic field that was 10 times stronger than you thought it would be.
Prof. WOLFE: That's right.
FLATOW: And you don't know why that is, you have a couple...
Prof. WOLFE: Not really. I mean, as I said, we have some ideas. We're going to test these ideas with some observations. We're going back to Green Banks again, we're going to look - well try to look at a much more distant galaxy than this one. We're going back - we're looking at a galaxy whose age is maybe one billion years when we see it. And if we see such a strong field in that object, then I would say the dynamo theory is in trouble.
FLATOW: In trouble?
Prof. WOLFE: Yeah...
FLATOW: So you...
Prof. WOLFE: So right now, I think it's still - it's a challenge but it's...
FLATOW: But you first want to checked the data...
Prof. WOLFE: Oh, absolutely.
FLATOW: Make sure you made the right - so you look at other galaxy to see that it wasn't a mistake that you had...
Prof. WOLFE: Exactly. We did that in our first observation, but you can't be too cautious in this field. And so, we're going to do it again, we're going to try to do it at other radio telescopes.
FLATOW: Well, of course, if you have a revolutionary idea like this, I mean, or discovery like this then you better go check it a few times.
Prof. WOLFE: You're absolutely correct, Ira. That's the first thing that occurred to us. We better check it, then double check it.
FLATOW: How does this fit in to the whole theory about how galaxy and stars form?
Prof. WOLFE: Well, it's an interesting question. I would say magnetic fields are normally ignored in theories of galaxy formation. One of the reasons is that they're difficult to compute, it brings in the field of magneto hydrodynamics which is another order - more complicated.
FLATOW: It makes your head hurt to think about that word.
Prof. WOLFE: What's that?
FLATOW: It makes your head swim - you have to think it. I mean, when we go to Astronomy 101, they don't talk about that...
Prof. WOLFE: No, they don't talk about it.
FLATOW: They talked about that little disc and everything else and all kind of stuff.
Prof. WOLFE: But I think they're going to have to because I think one of the other implications our discovery, independent of everything else, is that the gas that we look at is more highly magnetized than people had imagined. And what this ultimately does will suppress star formation and this - a lot of the objects that we look at high ratio stars these - when you look at galaxies in the distant past, most of the ordinary matter was in gas, not in stars, if you go far enough back in time. And what - if the object we look at is typical, OK, what this tells is that the gas is highly magnetized and this acts to suppress star formation because it is added pressure, that I was talking back, that resist the gravitational collapse of clouds as they - that's how we think stars form, and if a star's cloud just collapsed.
FLATOW: And you'd have to explain why the magnetism lessens so you could create the stars.
Prof. WOLFE: I'm sorry?
FLATOW: You'd have to explain why the magnetism suddenly was much less so the stars could be created.
Prof. WOLFE: Well, that's right. Somehow the fields will have to leak out of the gas or the gas would have to be much more compressed than the ones we're looking at. But I mean, if what we're looking at is typical, stars formation will be suppressed, and I guess than the other regions in this galaxy where this is not the case that's where a star is formed.
FLATOW: Well, good luck to you Dr. Wolfe.
Prof. WOLFE: OK. Thank you very much.
FLATOW: We'll check in when you get those other readings.
Prof. WOLFE: OK. Thank you.
FLATOW: You're welcome. Arthur Wolfe is professor in the Department of Physics an the Center for Astrophysics & Space Sciences at the University of California-San Diego. A bit baffled about take home message, why the magnetism - electromagnetism is 10 times what they thought it would be in a very, very young star. And they're going to go out and check their equipment and see what other galaxies look like, these young galaxies, not stars. We're going to take a short break, come back and change gears and talk about a very good rocket launch. Why four is a charm instead of three? So stay with us, we'll be right back.
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FLATOW: I'm Ira Flatow, this is Talk of the Nation Science Friday from NPR News.
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