A black hole with a mass of about one hundred thousand times our Sun has been discovered hiding in a cloud of molecular gas near the centre of the Milky Way. The finding, reported in a paper published online this week in Nature Astronomy, provides important insight on how supermassive black holes like the one at the very centre of our Galaxy may have been created.
It is well established that supermassive black holes of up to ten billion solar masses reside at the centres of galaxies. However, we do not know how they get so massive, especially as they appear to have been in place when the Universe was comparatively young - only a few hundred million years old. This conundrum could be solved if black holes of a few hundred thousand solar masses exist as seeds for their more massive counterparts. Unfortunately, such intermediate-mass black holes have persistently evaded detection, with only a handful of convincing candidates currently known.
Tomoharu Oka and colleagues use the high sensitivity and resolution of the Atacama Large Millimeter/submillimeter Array in Chile to observe a cloud of molecular gas 60 parsecs away from the Milky Way’s centre. They use simulations to infer that the kinematics of the gas in this cloud can only be explained by the presence of an intermediate-mass black hole hiding in its midst. The authors also find that the emission from this gas cloud closely resembles a scaled-down version of the quiescent supermassive black hole at the centre of our Galaxy.
Future work will now focus on monitoring this source to confirm its nature, as well as using this technique to discover more such intermediate-mass black holes.