Feast your eyes on the infrared, optical, and x-ray image above of M82, a nearby galaxy undergoing a burst of star formation. The inset shows observations from NASA's Chandra X-Ray Observatory, which was used along with data from ESA's XMM Newton in two papers led by Hua Feng. The two brightest point sources may be elusive IMBHs.
Astronomers made this determination based on the variability of the x-ray emission, as well as the x-ray spectrum, or how the light is spread out in energy. For one of these candidates, the variability of the x-rays and the spectrum of the disk around the black hole both indicate tens of thousands of solar masses.
We don't know what could produce a black hole of such size, except that it may be representative of a "seed" black hole that was formed early in the universe's history. Many of these are thought to have been the "seeds" of the supermassive black holes in the nuclei of galaxies today.
The other candidate intermediate mass black hole is thought to be a few hundred times the mass of the sun. This could have formed from the runaway collisions of massive stars in a cluster, which formed an unusually powerful supernova, leaving behind a big black hole. Or, many stellar-mass black holes may have collided to form this intermediate monster. Or, it could be something entirely unexpected.