Astronomers measure rare black hole

Researchers, including one of Indian-origin, have accurately measured and confirmed the existence of an elusive black hole, 400 times the mass of our Sun, in a galaxy 12 million light years from Earth.
Ranging from a hundred times to a few hundred thousand times the Sun's mass, these intermediate-mass black holes are so hard to measure and even their existence is sometimes disputed.
Little is known about how they form. And some astronomers question whether they behave like other black holes.
University of Maryland astronomy graduate student Dheeraj Pasham and colleagues succeeded in accurately measuring - and thus confirming the existence of - a black hole about 400 times the mass of our Sun in a galaxy 12 million light years from Earth.

Co-author Richard Mushotzky, a UMD astronomy professor, said the black hole in question is a just-right-sized version of this class of astral objects.
"Objects in this range are the least expected of all black holes," said Mushotzky.

While the intermediate-mass black hole that the team studied is not the first one measured, it is the first one so precisely measured, Mushotzky says, "establishing it as a compelling example of this class of black holes."
"For reasons that are very hard to understand, these objects have resisted standard measurement techniques," said Mushotzky.
Pasham focused on one object in Messier 82, a galaxy in the constellation Ursa Major.

Messier 82 is our closest "starburst galaxy," where young stars are forming.
Beginning in 1999 a NASA satellite telescope, the Chandra X-ray Observatory, detected X-rays in Messier 82 from a bright object prosaically dubbed M82 X-1.
Astronomers, including Mushotzky and co-author Tod Strohmayer of NASA's Goddard Space Flight Centre, suspected for about a decade that the object was an intermediate-mass black hole, but estimates of its mass were not definitive enough to confirm that.
Between 2004 and 2010 NASA's Rossi X-Ray Timing Explorer (RXTE) satellite telescope observed M82 X-1 about 800 times, recording individual X-ray particles emitted by the object.

Pasham mapped the intensity and wavelength of X-rays in each sequence, then stitched the sequences together and analysed the result.
Among the material circling the suspected black hole, he spotted two repeating flares of light. The flares showed a rhythmic pattern of light pulses, one occurring 5.1 times per second and the other 3.3 times per second.
The study was published in the journal Nature.