Which Came First: The Galaxy Or The Black Hole?

Robert Siegel talks with UT-Austin astrophysicist Karl Gebhardt about his team's discovery of a giant black hole in a tiny galaxy. The discovery contradicts traditional theories of galaxy formation.



Astrophysicists evidently have their own chicken and egg problem. Which came first, the galaxy or the black hole? In reading up on the latest black hole discovery, I've learned that recently the smart money has been on the galaxy. But the new discovery evidently adds weight to the argument that the black hole may have come first. The discovery is a giant black hole in a tiny galaxy.

It was spotted by an international team of astrophysicists. And joining us now from Austin, Texas, at the University of Texas, is professor Karl Gebhardt. Welcome to the program and congratulations on this discovery.

KARL GEBHARDT: Thank you. It's very nice to be here.

SIEGEL: I gather that a galaxy typically comes with a black hole and vice versa. What's so unusual about this black hole that you've spotted?

GEBHARDT: Right. So every galaxy typically comes with a black hole, but in this one, the mass of this black hole is about 100 times larger than what we had expected based on the typical galaxy.

SIEGEL: So how does this change whatever theoretical ideas there are about the creations of galaxies and black holes and which one comes first?

GEBHARDT: Right. So the general consensus is exactly as you said. You start with a galaxy. There's a lot of stuff in a galaxy. There's lots of gas and dust. That stuff will interact with itself and it will fall into the middle. If there is a black hole, the gas and dust will go into the black hole and feed the black hole and grow its mass. And this leads to a really nice theoretical prediction that there's a correlation between the amount of mass in the black hole and the amount of mass in the galaxy.

SIEGEL: Okay. Now, your huge black hole that you've discovered suggests that it would've had to be formed in a different way.

GEBHARDT: Exactly, because this violates that idea. You just - the amount of mass we're talking about for the size of the galaxy, first of all, the amount of gas and dust the galaxy would have to start out with is pretty enormous. And secondly, you'd have to get that material, all that material, down into the black hole. And we just don't understand right now the physical process that could allow that to happen 'cause it just doesn't want to make it in.

It's trying to jam way too much material into two small of a lake. So you're exactly right. We likely need a different mechanism.

SIEGEL: Well, is it possible that you've discovered something that is anomalous and that is a black hole but doesn't follow the rules that govern other black holes or would that be science fiction?

GEBHARDT: You're exactly spot on. And look, there are 100 billion galaxies in the observable universe, approximately, you know, plus or minus a large factor. There's got to be some weird oddballs out there and this could be just a super weird oddball. So what we've been doing is we have a big survey and we have a handful now of other galaxies with very similar properties to NGC1277, the one with the big black hole.

We haven't analyzed it at the level of detail, but the properties look similar enough that it tentatively suggests that these also have anomalously large black holes. And if that's the case, now we have a trend and now we have to do something about that in terms of the theory.

SIEGEL: Well, wouldn't you have to redefine this thing, in that case and, you know, call it a, you know, black and blue hole or something like that?

GEBHARDT: Something like that.

SIEGEL: I could've done better in physics if one of the answers was this is anomalous. It could be anomalous and not conform to any known rule that we have.

GEBHARDT: There you go. That's right. But this one, the black hole is about 15 percent of the mass of the galaxy and we just don't know how to make that. There are ideas that had been floated in the past that it's possible that black holes come first. Maybe in this case, something happened to feed a black hole at an enormous rate and then the galaxy assembled around it.

We don't have that worked out yet. That's where we're going, but right now, we're just going to sit on the observational side and really try to characterize what's going on in these systems.

SIEGEL: So there's a project for the 21st century...

GEBHARDT: There we go and it's a - exactly. And it's a project to keep the theorists busy, too. I always like to toss something at the theorists just so they can justify their existence.

SIEGEL: Well, Professor Gebhardt, congratulations to you and the whole team and thanks for talking with us.

GEBHARDT: Thank you very much.

SIEGEL: That's astrophysicist Karl Gebhardt of the University of Texas, Austin.




