Black Holes are heavenly objects with masses so large (> 1.4 times Solar Mass, termed the Chandrasekhar Limit) that even light cannot escape from their gravitational pull. As a consequence, a black hole cannot be directly seen. However, it can be indirectly detected by a) observing the motion of a neighboring/orbiting star or planet, b) detecting the light (e.g. X-Rays) emitted by the matter falling into the black hole. Recently, University of Michigan scientists, using the orbiting Chandra telescope, have found peculiar X-Ray emissions from a black hole which indicates that it has a mass of about 10,000 Suns. Such intermediate mass black holes have been theorized to exist, but this is the first time one has been detected.

ULX black hole in galaxy M74 (Courtesy: University of Michigan)
At the larger end, scientists have previously detected black holes a billion times the mass of the Sun (at the center of galaxies like our Milky Way). At the smaller end, there is strong evidence for the existence of black holes with about 10 solar masses. This is the first time an intermediate mass black hole has been found.
Lead researcher Jifeng Liu and his colleagues used Chandra to observe a black hole in the galaxy M74, which is about 32 million light years from Earth in the constellation Pisces. They found that this source exhibits strong, nearly periodic variations in its X-ray brightness every two hours, providing an important clue to the black holes’ mass. The black hole also fell into a class of sources called ultraluminous X-ray sources (ULXs) because they radiate 10 to 1000 times more x-ray power than Neutron stars and stellar mass black holes.
There are no convinciing explanation (yet) of how these black holes are formed. Some theories under consideration are that intermediate-mass black holes form as dozens or even hundreds of black holes merge in the center of a dense star cluster, or that they are the remnant nuclei of small galaxies that are in the process of being absorbed by a larger galaxy.