Astronomers spot signs of intermediate black hole

The use of radio telescopes is helping astronomers at the National Astronomical Observatory of Japan uncover hidden black holes within the Galaxy. Their latest discovery could be a vital piece in the puzzle as to how supermassive black holes are formed.

Artist’s impression of gas clouds being scattered by an intermediate mass black hole
Credit: NAOJ/Tomoharu Oka (Keio University)

Astronomers at the National Astronomical Observatory of Japan have discovered evidence for an ‘intermediate mass’ black hole, which could be key to understanding how supermassive black holes at the centre of galaxies form and evolve.

The team found an enigmatic gas cloud called CO-0.40-0.22, 200 lightyears away from the centre of the Galaxy, and noticed that the gas within the cloud is travelling at a wide range of speeds.

Using the Nobeyama 45m radio telescope at the observatory and the ASTE radio telescope in Chile, they were able see that the cloud has an elliptical shape and consists of a low density area with a wide velocity dispersion of 100 kilometres per second, and a second denser area with a narrow velocity dispersion.

However, there are no holes inside the cloud and no compact objects lurking within, suggesting that this discrepancy between the two areas is not caused by an object generating energy in the cloud, such as a supernova explosion.

The team, led by Professor Tomoharu Oka at Keio University, created computer simulations of gas clouds being flung by a source of strong gravity. In these simulations, the gas clouds are attracted by the source, increasing in speed as they approach it, then decreasing in speed as they pass it.

Simulated models using a gravity source 100,000 times the mass of the Sun inside an area with a radius of 0.3 lightyears provided the best fit to explain the discrepancy.

“Considering the fact that no compact objects are seen in X-ray or infrared observations,” says Oka, “as far as we know, the best candidate for the compact massive object is a black hole.”

If the team’s conclusion is proven to be correct, it will mark the first ever detection of an intermediate mass black hole, which are thought to be bigger than stellar mass black holes yet smaller than the supermassive black holes that can be found at the centre of galaxies.

Astronomers don’t yet know for sure how supermassive black holes are formed, but one theory suggests they could be created through a merger of multiple intermediate mass black holes, which so far remain hypothetical. If this latest study is correct, it could provide a new and significant revelation in the mystery of black holes' evolution.


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