Scientists from Keio University in Japan have unveiled the best evidence we have for an intermediate-mass black hole – and it’s right in our Milky Way. Intermediate-mass black holes have eluded astronomers, who have found hints of both star-sized black holes and supermassive black holes. But the discovery of the mid-sized black hole could help scientists understand why supermassive black holes grow so immense.

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The formation of supermassive black holes has been a mystery for astronomers, but this new study might provide an explanation for how they form. The researchers from Japan said in their research that mid-sized black holes could merge to form supermassive black holes, but there’s been little evidence for the existence of intermediate-mass black holes – until now.

Related: Supermassive black holes offer hint at structure of the universe

Last year, a team led by Tomoharu Oka of Keio University reported a strange cloud of molecular gas, dubbed CO-0.40-0.22, in our Milky Way. A team also led by Oka then scrutinized the cloud with instruments such as the Atacama Large Millimeter/submillimeter Array (ALMA) and found a dense clump of gas near the cloud’s center, and a nearby radio wave source, CO-0.40-0.22*, that has similarities to the supermassive black hole Sagittarius A*. According to Oka, the similarity “supports the notion that CO-0.40-0.22* is an intermediate-mass black hole.”

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Scientists have expressed excitement about the discovery; Swiss Federal Institute of Technology astronomer Kevin Schawinski told Science Magazine, “It’s a very careful paper and they have gorgeous data. It’s the most promising evidence so far.”

If CO-0.40-0.22* is verified as a black hole, its presence could offer support to the idea our galaxy has gotten bigger by cannibalizing smaller neighboring galaxies. The Japanese scientists think CO-0.40-0.22* could be a former dwarf galaxy core that could have been absorbed into the Milky Way, and could one day be subsumed by Sagittarius A*.

The journal Nature Astronomy published the study online this week.

Via Keio University, Science Magazine, and ScienceAlert

Images via Keio University and NASA/JPL-Caltech