Sagittarius A* (pronounced Sagittarius A Star), the supermassive black hole at the centre of the Milky Way, is spinning in an unusual way, and scientists now believe they may know why. Based on new data from the Event Horizon Telescope, researchers suggest that this cosmic giant likely merged with another black hole billions of years ago. This colossal collision would explain the black hole’s rapid, misaligned spin, which differs from the rest of the galaxy’s orientation.

The Role of Mergers in Black Hole Evolution

Located 26,000 light-years from Earth, Sagittarius A* is a massive object, 4 million times the mass of the Sun. Its fast spin and odd tilt have long puzzled astronomers, but new research points to a violent past.

According to a study published in the Nature journal and led by Yihan Wang, an astrophysicist at the University of Nevada, Las Vegas (UNLV), the black hole’s strange spin is best explained by a merger with another supermassive black hole. This event could have occurred around 9 billion years ago and may have drastically altered Sagittarius A*’s spin.

Supermassive black holes are believed to grow not only by absorbing nearby gas and dust but also by merging with other black holes when galaxies collide. Bing Zhang, a professor of physics and astronomy at UNLV and co-author of the study, explained that the merger likely happened after the Milky Way collided with the Gaia-Enceladus galaxy. This adds significant evidence to the theory that black holes can expand by merging with others of their kind.

Future Discoveries Await

Astronomers are hopeful that future space-based projects, such as the Laser Interferometer Space Antenna (LISA), set to launch in 2035, will help uncover more about the history of supermassive black holes. These tools will detect gravitational waves produced by such mergers, providing even more insights into the dynamic evolution of galaxies and their black holes.