Physicists Determine Cause of "Runaway" Supermassive Black Hole

In September 2022, astronomers observed a strange feature in a galaxy 7.5 billion light-years away, called RBH-1, which was a supermassive black hole ejected from its host galaxy. The feature was a thin line extending over 202,000 light-years, with an unresolved object at its end moving at 1,000 km/s. The team from the University of California, Santa Barbara (UCSB) used Hubble and James Webb data to trace the black hole back to its origin and concluded it was formed by a violent merger event. The study, published in Physical Review Letters, is the first to observe such an event.

The black hole, RBH-1, was previously identified as a moving object, and the team led by Tousif Islam simulated hundreds of thousands of black-hole pairs to determine its origin. They found that the parent black holes were similar in mass, with one being up to six times as massive as the other. Both were spinning rapidly and misaligned, with the heavier one spinning at 70-75% of the maximum allowed by General Relativity. This discovery shows how extreme the spins can be, and how such mergers can produce powerful gravitational waves.

This finding provides new insights into the evolution of supermassive black holes and their host galaxies. The study suggests that the black hole was formed by the merger of two galaxies 70 million years ago, and the galaxies themselves had misaligned rotations. The results also highlight the importance of gravitational waves in understanding black hole mergers, and how these events can be detected through telescopes like Webb and future observatories like LISA. The research will help future studies that combine gravitational wave physics with galactic mergers.

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