Wednesday, January 7, 2009

Supermassive Black Holes May Form Galaxies

It is well accepted that at the center of a large galaxy you are going to find a super massive black hole. Interestingly, the size of the black hole at the center of the galaxy tends to have a constant mass as a proportion to the mass of the surrounding galaxy. The proportion is roughly a tenth of a percent. What was not known was which came first. Does the galaxy lead to the black hole or the other way around?

To figure this out scientists looked back in time to young galaxies, by looking extremely distant galaxies. When the did this, scientist found that in those young galaxies the mass of the black hole was larger in proportional terms then older galaxies. This seems to indicate that the super massive black holes somehow grow the galaxy to reach the current proportion.

There are still a number of unanswered questions, but this seems a good step in the finding the facts to let us come to reasonable conclusions.

"Mind you, as scary and big as these galactic black holes are, they are still a tiny fraction of the mass of their host galaxy’s bulge, about one-tenth of a percent, in fact. And that’s just for the bulge; the black hole is only about a thousandth of a percent of the total mass of the entire galaxy.
But if we look at very distant galaxies, we see them as they were when they were much younger, only a billion or two years old. If black holes grow more quickly or more slowly than their host galaxies, then looking that far back in distance and time may make that easier to see. This is what Chris Carilli, of the National Radio Astronomy Observatory (NRAO), and an international team of astronomers did.

Radio observations of young galaxies find that the black holes form first,
or at least grow more quickly than the galaxy.

When they looked at distant, young galaxies, they found that the black holes were more massive relative to their host galaxies than they are today! That’s a big result. It implies very strongly that somehow, the black holes grew first, with the galaxies growing more slowly around them.


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