Astrophysicists have uncovered new evidence suggesting that the supermassive black hole (SMBH) at the center of the Milky Way, Sagittarius A* (Sgr A*), likely formed around nine billion years ago through a significant galaxy merger. The study, conducted by researchers Yihan Wang and Bing Zhang from the University of Nevada, Las Vegas, was published in Nature Astronomy and highlights the critical role mergers play in the formation and evolution of SMBHs.
Sagittarius A*, which has a mass approximately four million times that of the Sun, exhibits unusual characteristics, including rapid spin and a misalignment with the Milky Way’s plane. According to the researchers, these features suggest a past merger, likely with a satellite galaxy known as Gaia-Enceladus. Using data from the Event Horizon Telescope (EHT) and advanced computer simulations, the team was able to model how such a merger would affect the black hole’s properties.
The study builds on groundbreaking EHT observations, which in 2022 provided the first direct image of Sgr A*. By simulating the growth of black holes through accretion and mergers, the researchers concluded that a 4:1 mass ratio merger could explain the observed spin characteristics of Sgr A*. This merger event would have occurred following the collision of the Milky Way with Gaia-Enceladus.
“This discovery supports the theory of hierarchical black hole mergers and offers new insights into the dynamic history of our galaxy,” said Zhang, a distinguished professor of physics and astronomy at UNLV.
As gravitational wave observatories like LIGO and Virgo continue to detect black hole mergers, the study hints at future breakthroughs in understanding SMBHs. Upcoming space missions, such as NASA’s Laser Interferometer Space Antenna (LISA), expected to launch in the 2030s, are poised to detect gravitational waves from supermassive black hole mergers, further unraveling the mysteries of these cosmic phenomena.
This research not only enhances our understanding of Sgr A* but also opens new avenues for studying the formation and growth of supermassive black holes across the Universe.
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