X-ray observations point to mid-sized black hole

Stephen Withers
Thursday, 17 May 2007 13:59

Science - Space

NASA astronomers have used observations from the ESA's XMM-Newton orbiting X-ray observatory to identify what appears to be intermediate mass black hole.

Small black holes - those with masses around five to 20 times that of the Sun - are known to occur when massive stars collapse. And the huge black holes at the centres of galaxies appear to have masses up to a thousand million times greater than the Sun.

Although there is no widely accepted theory for the formation of black holes between these two extremes (known as intermediate mass black holes, or IMBHs), astronomers at the Goddard Space Flight Center have determined that a black hole 16 million light years away in the NGC 5408 galaxy is around 2000 solar masses..

"This is one of the best indications to date for an IMBH," says Goddard's Tod Strohmayer.

The technique used was developed by Lev Titarchuk, another Goddard scientist, in 1998. Approximately periodic variations in X-ray intensity have been linked to changes in a black hole's accretion disk (orbiting gas that gradually falls into the black hole). The longer the period, the greater the black hole's mass.

These and other measurements suggest the NGC 5408 black hole is an IMBH. "We had two other ways of estimating the mass of the black hole, and all three methods agree within a factor of two," said Strohmayer's colleague Richard Mushotzky. "We don’t have proof this is an IMBH, but the preponderance of evidence suggests that it is."