Black Hole Strikes Neighboring Galaxy Astronomers have captured an image of a jet of high energy particles leaving a black hole at the center of one galaxy to strike the edge of neighboring galaxy. Black hole jets can produce high levels of radiation, potentially sparking new star formation in their path. The black hole is about 1.4 billion light years away.
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Black Hole Strikes Neighboring Galaxy

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Black Hole Strikes Neighboring Galaxy

Black Hole Strikes Neighboring Galaxy

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IRA FLATOW, host:

Up next, an unusual look at some rather unneighborly behavior. Scientists working with data from the Chandra X-ray Observatory have documented a rare occurrence. Perhaps you've seen the picture, a photo, a graphic of this gorgeous event in the galaxy about 1.4 billion light-years from ours. There is a super-massive black hole actually attacking its neighbor. It's spewing out a jet of radiation at it - but it's pretty far away, not to worry. Scientists say that they two galaxies appear to be merging together.

Joining me now to talk more about it is Martin Hardcastle, senior lecturer in astrophysics at the University of Hertfordshire in Hatfield, U.K. He joins us by phone.

Thanks for staying up late for us today, Dr. Hardcastle.

Dr. MARTIN HARDCASTLE (Senior Lecturer in Astrophysics, University of Hertfordshire): That's no problem. Glad to be here.

FLATOW: What is actually happening? One galaxy is attacking the other?

Dr. HARDCASTLE: Well, that's - you know, that's an anthropomorphic way of putting it. This galaxy is emitting large jets of (unintelligible). Beware that that's not unusual. We know a large of them. And what's unusual about this system is that the neighboring galaxy - you know, purely by chance - we imagine this has wandered into the path of the jet. And because it's in the path of the jet, the jet can house various (unintelligible) that it rather interesting. And also the attraction disrupts the jet, so we get to see things - see something that is fairly rare.

FLATOW: Mm-hmm.

Dr. HARDCASTLE: But with that issue over us, there's no malice involved.

(Soundbite of laughter)

FLATOW: Why is this so rare? You would think with all the galaxies out there and there are hundreds of billions of them, this might be going on quite often.

Dr. HARDCASTLE: Yes. There are several pieces of it and it suggested it has happened in other systems in the past. Well, we think we saw evidence of interaction that have taken place in the distant past, say, tens of millions of years ago, hundreds of millions of years ago, between a (unintelligible) and a neighboring galaxy. This is the first time we'd actually seen it as its going on. And that's - the real reason why it's so rare is this place is very big and very empty.

FLATOW: Mm-hmm.

Dr. HARDCASTLE: So most of the time these jets are going out into the empty space, especially very little material. And they don't hit anything they get off until they stop.

FLATOW: How and how quickly is the merging of these two galaxies occurring?

Dr. HARDCASTLE: Well, they - the merger of the galaxy is actually a very slow process. It can take billions of years to be complete. So I would guess we have the merger. The merger may one that'd been going on for a hundred million years. It may take another few hundred million years to be - to get to the stage where we look at that galaxy and say, yeah, that's just one big galaxy running on two smaller galaxies. So that's a very slow process.

FLATOW: So if you took another picture of it next week, you would not see any…

Dr. HARDCASTLE: Absolutely, yes. Next week, it will look very much the same as this week. In fact, the data that we have combined to study the subject, had taken over decades, you know. The Chandra images is somewhat old. The spectrology is (unintelligible). The Hubble Space Telescope which is recent. The radio data are older and so on. Now, these things don't change on human timescales. We have - we would like to stay around for another million years or so and see what happens. But we're not getting that option.

FLATOW: How - what is driving the jet out to the other galaxy. What is the mechanism that's going on here?

Dr. HARDCASTLE: That's a great question. And quite honestly we don't know in detail how these jets are formed in any of these systems. So (unintelligible) jet emanating from close to a black hole are reasonably common. But the jet generation mechanism is a mystery, because it happens on very small scale. It happens very close to the black hole, and we just don't have telescopes that can choreograph that deep.

So while we know that a galaxy sends a black hole can generate jets, and there are a bunch of other jets in the universe that can generate jets in a fairly similar way, the actual mechanism is not very well known. Now, there are a bunch of models and various people will tell you they know the answer. That observation really can't say. We just know that this does happen, it's a fact. You know that there is a - there are systems that generate these jets.

And one of the things we have to do by observing them in this way and observing their interaction with other galaxies is to understand what (unintelligible) and what - how much energy they carry and so on, which could give us some clues about their ultimate origin.

FLATOW: Question from "Second Life" from Guysoft(ph) who asks: Is the merging violent with stars crashing or is it smooth?

Dr. HARDCASTLE: Well, it depends how you want to look at violence. Stars almost never crash because stars are very small relative to the space between them. So there won't be very many strong interactions between stars. It can happen, but it's a very, very rare process. However, what does happen in the process of the galaxy merger is that the gravity of the two galaxies pulls the stars after their orbits within the galaxies. And so in some of the images that we showed in the release, you can see tails of stars trailing off from the two galaxies that are merging that's been stripped off by gravity.

Now, whether that actually does anything very much to the stars or whether it just, you know, perturbs their orbit, means that they're very different in all the different places it would have been in outer space.

FLATOW: You know, the pictures are so gorgeous it's almost like they're artistic in a sense.

Dr. HARDCASTLE: Yes. I mean, the thing that drew our attention to this apart from the rarity is just the beauty of the images. I mean, it's a great tribute to the (unintelligible), the wide, you know, the wide range of wavelengths we can put altogether. I mean, the combined imagery shows everything from radio up to x-ray, which is a vast range in wavelengths much, much more than the human eye can see.

FLATOW: Yeah.

Dr. HARDCASTLE: And the instruments that we have now - well, they allow us to do this very well.

FLATOW: Let's go to Steve in Margate, New Jersey. Hi, Steve.

STEVE (Caller): How are you doing, Ira? You know, I was going to try to get through earlier about one of the great science stories of the year - the merging of this galaxies. But from what I understand that I've read (unintelligible) my NASA and place(ph) Web sites, that the Andromeda galaxy and the Milky Way galaxy are going to smash into each other in, like, several five billions years or something. And this might be something we should be concerned about. Although I think that NASA won't be (unintelligible).

(Soundbite of laughter)

FLATOW: We'll just get past the holiday season, I think.

STEVE: Yeah, I know. But this is what I understand, that we have a big, black hole in the middle of our galaxy and Andromeda probably has a big, black hole in the middle of its galaxy, so this could turn out to be a big, ugly mess.

FLATOW: Let me ask the doctor. Dr. Hardcastle?

Dr. HARDCASTLE: Yes. Yes, I think that's absolutely right. I mean the - I think that's a very perceptive question in fact. I mean, yes, we know that the - we know that activity from black holes who we think with that fairly sure that activity can be triggered by mergers. The reason for that is that the black holes in the normal situation is sitting down in the middle of the galaxy and they have nothing to feed on, and they need to be - the need materials to be falling into them to generate these jets. So black holes on its own doesn't do anything.

And the merger can cause gas and stars and so on to fill - fall into the black hole by perturbing the orbits and, again, in the same sort of way as we see the stars being perturbed with the gas and so on can be perturbed and fall into the sun. When that happens, the black hole can acquire a source of fuel. So when Andromeda and the Milky Way merge, (unintelligible) it's really quite likely that they will be some active galaxy outburst.

Now, a few other things would have to happen for us on Earth to need to worry. To our listener, first of all, the timescales are a bit long. We've been on Earth a very short time compared to the timescale we're talking about. I, you know - and I - fingers crossed we managed to last that long. You know, species don't generally last that long. And, of course, we have to worry about how the sun getting too hot and so on before that time. Well, that's suppose we last until then. When the merger happens, then it's worth bearing in mind that these jets and the radiation that come from active galaxies are quite directional. So we have to be unlucky, the jet would have to start off and it would have to point directly at us. And that's what - which is what it's doing to this compiling in galaxy right now.

So, I think - I mean, for most of the inhabitants of the larger galaxy in the (unintelligible) system what you have is a very spectacular fireworks show. It's not going to do you any harm. It happens that there's a whole small galaxy in the way of the jet. But in the case of the Milky Way and Andromeda merging, we would have to be very unlucky in many ways to be significantly affected. But you might certainly expect to see that fireworks show.

FLATOW: Yeah. If we're still around. The…

Dr. HARDCASTLE: If we're around in a billion years.

FLATOW: This is TALK OF THE NATION: SCIENCE FRIDAY from NPR News. I'm Ira Flatow talking with Martin Hardcastle in the U.K.

A quick extra question our listeners always want to know. Why don't these black holes suck up everything? I mean, to eat everything up. Why aren't they like cosmic vacuum cleaner?

Dr. HARDCASTLE: Well, essentially because they're just behaving as sources of gravity like anything else. And it's the same reason why the sun doesn't suck up the air. The sun is a vary massive object and it's very close to us. And when you think gravity pulls in, so why doesn't the air fall into the sun. And that's what the answer is. The Earth is in orbit and that orbit is stable, and that's something knocks it out a little bit. It's going to carry on going round and round before - you know. If you remember the centrifugal and centripetal forces and so on. You that the force of gravity is pulling us in, but we're trying to spin out because we're orbiting.

Now, in a stable situation, the galaxy that's pretty much what happens. We can - in fact, look at the orbits of stars around the central black hole in our own galaxy. That's how we know so much about it. And we can see that those orbits are stable and know that though the stars can sometimes pass very close to the black hole, they're not being swallowed up, because they're just orbiting away. And what happens occasionally, if there's something that perturbs those orbits through (unintelligible) an interaction with another star, two stars come close together, the orbit change slightly, and then the star might fall in.

In the same sort of way the reason why we see black holes in the centers of galaxies - not all galaxies, but stuffed into (unintelligible) activity is (unintelligible) because material is able to fall into them for some reason, whether it be gravitational perturbations or whether it'd be they're dumping a lot of mass onto the black hole by means of a merger, for example.

FLATOW: Mm-hmm. So you think that now that you've found this rare occurrence, it's back to hunting for more or…

Dr. HARDCASTLE: Oh, this was a - this is almost - I mean, it's - we found it interesting because it's so rare, and it's not - it wasn't what we were looking for at the time we started to look in the subject. In fact, we were looking for else, as often happen in astronomy. Now, what we hope to do with this rare event is to understand a little more about how the jet works. And by seeing how the jet is being disturbed, it's being perturbed by this interaction, we might be able to find out where the (unintelligible) is in the numerical modeling, for example. How the jet fluid behaves. And so, part - none more than what the jet is made of.

Now, from - I mean, our interest is more in the (unintelligible) of the jet than it is in the terrible fate of all the people in this (unintelligible) of galaxy. (Unintelligible) - that's what we're really trying to find out where we have to go from here.

FLATOW: Well, we wish good luck to you.

Dr. HARDCASTLE: Thanks very much.

FLATOW: Have a happy holiday season from us on this side of the planet.

Dr. HARDCASTLE: You too.

FLATOW: Martin Hardcastle, senior lecturer in astrophysics at the University of Hertfordshire in Hatfield, U.K.

Have a great holiday season. Merry Christmas if you're celebrating it.

I'm Ira Flatow in New York.

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