Hubble spies homeless black hole


Wednesday, September 14, 2005 Posted: 1714 GMT (0114 HKT)

WASHINGTON (Reuters) -- A supermassive black hole appears to be homeless in the cosmos without a galaxy to nestle in, Hubble Space Telescope scientists reported on Wednesday.

Most monster black holes lurk at the heart of massive galaxies, slurping up matter from the galactic center with a pull so strong that nothing, not even light, can escape.

But a team of European astronomers reported in the journal Nature that a particular black hole some 5 billion light-years away has no evidence of a host galaxy. A light-year is about 6 trillion miles (10 trillion km), the distance light travels in a year.

The black hole was detected when the scientists went hunting for quasars -- extremely bright, small, distant objects that are strongly associated with black holes. Astronomers believe a quasar is produced by cosmic gas as it is drawn toward the edge of a supermassive black hole.

Most quasars and black holes are in the middle of supermassive galaxies and in their survey of 20 relatively nearby quasars, the scientists found 19 followed this expected pattern. But one showed no signs of having a galactic home.

The astronomers, using the Hubble telescope and the Very Large Telescope in Chile, reported that this rogue black hole may be the result of a rare collision between a seemingly normal spiral galaxy and an exotic object harboring a very massive black hole.

One problem in quasar-hunting is that they are so bright, they outshine most galaxies that surround them, just as the headlights from an oncoming vehicle can make the vehicle hard to see. So even if a surrounding galaxy is present, it can be difficult to detect.

The European astronomers used the two telescopes to overcome this problem by comparing the quasars they were watching with a reference star. This let them differentiate the light from the quasar from the light from any possible underlying galaxy.