Astronomers have uncovered new evidence suggesting that the Milky Way’s supermassive black hole, Sagittarius A* (Sgr A*), may have formed through a violent merger with another black hole billions of years ago. The findings, published on Sept. 6 in Nature Astronomy, help explain why the black hole is spinning incredibly fast and misaligned with the galaxy’s rotation.

A Collision That Shaped the Milky Way

Located 26,000 light-years from Earth, Sagittarius A* is an enormous black hole weighing 4 million times the mass of the Sun and stretching 14.6 million miles (23.5 million kilometers) wide. Scientists have long been puzzled by its rapid spin and unusual tilt relative to the Milky Way’s disk. Now, researchers using data from the Event Horizon Telescope, which captured the first image of Sgr A* in 2022, believe they have an answer.

Simulating different scenarios, the team found that the best explanation for the black hole’s strange orientation is that it merged with another supermassive black hole roughly 9 billion years ago. This timing aligns with the Milky Way’s merger with the Gaia-Enceladus galaxy, suggesting that the galactic collision may have brought another black hole close enough for Sgr A* to absorb it.