Japanese researchers find signs of galaxy’s second-largest black hole


Researchers at Keio University said they have detected signs of the second-largest black hole in our galaxy.

The finding by the team led by professor Tomoharu Oka may support the hypothesis that supermassive black holes, such as the one located at the center of the Milky Way, are formed by mergers of intermediate mass black holes.

According to their study, described in Astrophysical Journal Letters earlier this month, the team observed a molecular cloud, or a cluster of gas with high temperatures and high density, in the central area of the galaxy, some 27,000 light-years from Earth.

By scrutinizing the cloud using radio telescopes, including the National Astronomical Observatory’s Nobeyama telescope in Nagano Prefecture, it found that movements of a part of the cloud had wide velocity dispersion.

This indicates existence of a large source of gravity near the cloud, which is highly likely to be an intermediate mass black hole about 100,000 times bigger than the mass of our sun, as there are no other ordinary celestial bodies close by, the research team said.

It is known that a supermassive black hole, some 4 million times larger than the mass of the sun, is located in the galactic center, but how it has evolved remains a mystery.

The possible existence of an intermediate mass black hole near the galactic center signals the possibility that the gigantic black hole may have grown by swallowing similar midsize black holes, the research team said.

Oka said he will aim to observe more molecular clouds around the center of the Milky Way.