For the first time, a system of three black holes has been identified, locked in a complex dance akin to that of the Earth and Moon orbiting each other while simultaneously circling the Sun. The presence of the third black hole, which had remained hidden until now, was inferred from gravitational waves detected in 2019 by the American LIGO observatory. These waves were produced by the merger of the other two black holes and have now been reanalyzed in a study led by the Chinese Academy of Sciences and published in *The Astrophysical Journal Letters*.
The 2019 detection captured ripples in spacetime caused by the violent merger of two black holes with masses of 23 and 2.6 times that of the Sun, respectively. The significant disparity in their masses surprised astronomers. Now, researchers led by Shu-Cheng Yang propose this imbalance can be explained by the gravitational influence of a third, supermassive black hole—at least 100,000 solar masses—which provided the necessary push for the collision.
By running simulations with the available data, the study’s authors identified a characteristic signature confirming the third black hole’s presence. A subsequent re-examination of the LIGO data proved this signature was indeed there.
“This is the first international discovery of clear evidence for a third object in a binary black hole merger event,” stated study co-author Wen-Biao Han.
The triple system has now likely transformed into a more classic binary system. According to the researchers, the new black hole born from the merger will probably continue to orbit its colossal partner for billions of years before finally being consumed.
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