September 14, 2005

Hubble spies homeless black hole

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, 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.

Further information is available online at