Destiny Awaken

By KENNETH CHANG

Published: July 6, 2009

In the universe of black holes, there are small black holes, single stars that collapsed upon them, and there are gargantuan black holes, behemoths at the center of galaxies that weigh millions to billions times more.

For years, there’s been an astronomical Goldilocks question: Are there black holes not too big and not too small? Astronomers have made several claims of detecting black holes of such an in between size, with a mass of, say, hundreds of stars, but none of the claims have been entirely convincing.

In the current issue of the journal Nature, a team of scientists report the latest, and perhaps the most compelling, candidate yet for an intermediate mass black hole. (If these black holes exist, they could result from a merger of stellar black holes or a collision of two stars.)

Detecting and describing black holes is a tricky business, of course, because they do not emit light. But the material falling into a black hole does emit radiation, and all of the claims for intermediate black holes are based on the X rays’ being brighter than what the theoretical models allow for a stellar size black hole.

But theoretical astrophysicists, being theoretical astrophysicists, are not convinced that brighter Xrays necessarily mean a bigger black hole. They can concoct situations like the focusing of Xrays into a tight, bright beam where a not-so-big black hole can be brighter than expected.

The new object, called HLX1 and 290 million light-years away, is about 10 times as bright as the brightest previous intermediate-size black hole candidate, which makes it more convincing.

“As you go to higher and higher luminosities you need more elaborate scenarios to explain them,” said the lead author of the Nature paper, Sean Farrell, an astronomer at the University of Leicester in England.

The astronomers estimate that HLX1 is more than 500 times the mass of the Sun.

http://www.nytimes.com/2009/07/07/science/space/07obastro.html?_r=1&ref=science