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miércoles, 10 de junio de 2009

Black Hole Much More Massive Than Expected

When astronomers finally got access to a powerful supercomputer to recalculate the mass of a neighboring galaxy, they got a huge surprise.

The giant elliptical galaxy Messier 87 has a black hole two to three times larger than imagined, measuring about 6.9 billion times the mass of the sun.

"I am getting a little suspicious that some of the (computer) models in the past are wrong," University of Texas astronomer Karl Gebhardt told reporters at the American Astronomical Society meeting in Pasadena, Calif., this week. "This has implications for black holes in the other galaxies that have been measured."

Situated roughly 50 light-years from Earth, M87 is the largest and brightest galaxy within the Virgo Cluster and one of the most well-studied objects in the universe. Of all the relatively nearby galaxies, M87 is the biggest and it has the biggest black hole.

Gebhardt and colleagues used one of the world's most powerful supercomputers to fold in previously uncalculated attributes of the galaxy, including its so-called "dark halo" -- a spherical region beyond the galaxy's visible structures that contains dark matter gravitationally tied to the object."In all of our (previous research) I said including the dark halo wasn't important and I was wrong," Gebhardt said. "What is surprising is that in order to get the small scale analysis correctly you have to include what the stars are doing at the outer envelope of the galaxy. You have to understand the effect of the dark halo."

The research may impact scientists' thinking about how galaxies form, a phenomenon that is not well understood.

"We're seeing that black holes play some very important role in galaxy formation but we don't know what it is," astronomer Sarah Salviander, with the University of Texas, told Discovery News.Gebhardt said his team's research may resolve a puzzle about why distant, ancient galaxies known as quasars seem to have black holes so much larger than their more modern kin.

"We've asked ourselves for a few decades now why don't we see any of these super-super-massive black holes nearby?" he said.

Increasing the masses of local galaxies' black holes by two or three times, "almost makes the problem go away," he added.

Salviander, who is using the Sloan Digital Sky Survey results to study the relationship between a black holes and host galaxies, said she's not so sure there was ever a problem in the first place.

Perhaps there are lots of more modestly sized black holes in very distant galaxies, Salviander pointed out. It's just that astronomers can't see them.

Gebhardt and colleagues plan to follow up their computational studies with new observations of M87 that are expected to definitely prove the size of its black hole. A research paper detailing the team's results is due to be published in an upcoming issue of The Astrophysical Journal.

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