Mega collision with another galaxy 9 billion years ago created Milky Way black hole

The supermassive black hole located at the centre of our galaxy has been spinning extremely fast and out of orientation with the rest of the galaxy. The reason behind this behaviour and how it came into existence has been a mystery.

Now a new study seems to have the answers to both the questions.

Sagittarius A*, 26,000 light-years away from us, is a gargantuan tear in space-time. It is four million times the mass of our sun and 14.6 million miles (23.5 million kilometres) wide.

The telescope that first captured the black hole's image in 2022 had a lot more data about it. This data was studied by researchers, who believe that Sagittarius A* was born from a cataclysmic merger with another giant black hole billions of years ago. The findings published on September 6 in the journal Nature Astronomy say that the black hole is still showing the effects of this violent collision.

"This discovery paves the way for our understanding of how supermassive black holes grow and evolve," study lead author Yihan Wang, an astrophysicist at the University of Nevada, Las Vegas (UNLV), said in a statement.

"The misaligned high spin of Sgr A* indicates that it may have merged with another black hole, dramatically altering its amplitude and orientation of spin."

Supermassive black holes

As per the scientists, Sgr A* was born just like any other black hole - after the collapse of a giant star or gas cloud. It then started gobbling up anything that came too close. Black holes can slowly become monstrous in size and feed on other supermassive black holes.

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"This merger likely occurred around 9 billion years ago, following the Milky Way's merger with the Gaia-Enceladus galaxy," study co-author Bing Zhang, a professor of physics and astronomy at UNLV, said in the statement.

Supermassive black holes merge when entire galaxies merge. Milky Way has had several such mergers and collisions in the last 12 billion years, experts say. But, scientists are not sure about the role of black hole mergers in creating supermassive black holes. Can simply feeding on gas and dust turn a black hole into a supermassive black hole?

The new discovery "provides insights into the dynamic history of our galaxy," Zhang added.