Astronomers using the Nobeyama 45-m Radio Telescope have detected signs of an invisible black hole with a mass of 100 thousand times the mass of the Sun around the center of the Milky Way. The team assumes that this possible “intermediate-mass” black hole is a key to understanding the birth of the supermassive black holes located in the centers of galaxies.

A team of astronomers led by Tomoharu Oka, a professor at Keio University in Japan, has found an enigmatic gas cloud, called CO-0.40-0.22, only 200 light-years away from the center of the Milky Way. What makes CO-0.40-0.22 unusual is its surprisingly wide velocity dispersion: the cloud contains gas with a very wide range of speeds. The team found this mysterious feature with two radio telescopes, the Nobeyama 45-m Telescope in Japan and the ASTE Telescope in Chile, both operated by the National Astronomical Observatory of Japan.

The velocity dispersion is wide enough with no holes inside of the cloud. Also, X-ray and infrared observations did not find any compact objects. These features indicate that the velocity dispersion is not caused by a local energy input, such as supernova explosions. The team performed a simple simulation of gas clouds flung by a strong gravity source. In the simulation, the gas clouds are first attracted by the source and their speeds increase as they approach it, reaching maximum at the closest point to the object. After that, the clouds continue past the object and their speeds decrease. If that is the case, this is the first detection of an intermediate-mass black hole. These results open a new way to search for black holes with radio telescopes. “The on-going wide area survey observations of the Milky Way with the Nobeyama 45-m Telescope and high-resolution observations of nearby galaxies using the Atacama Large Millimeter/submillimeter Array (ALMA) have the potential to increase the number of black hole candidates dramatically.”