When Two Massive Black Holes Merged And Went Flying Across Cosmos

A rare instance of a supermassive black hole merger has been observed, resulting in a black hole exhibiting an unusually high proper motion. The New Scientist reported that this event holds substantial scientific significance, providing direct evidence for SMBH merger dynamics and their role in galactic evolution. 

Marco Chiaberge of Johns Hopkins University in Maryland and his colleagues have discovered evidence of a supermassive black hole (SMBH) being ejected from its galaxy, 3C 186, at more than a thousand kilometres per second.

Previous observations using the Hubble Space Telescope revealed that the galaxy's quasar-an intense light source powered by a black hole- was not in its expected position. Further analysis of the star distribution in the galaxy showed that the SMBH was about 33,000 light-years away from the galactic center, suggesting it had been displaced by a major event, possibly a galactic merger.

To investigate further, Chiaberge's team used the Very Large Telescope in Chile and the Subaru Telescope in Hawaii to analyze the black hole's emitted light. They found that light from its accretion disk-where matter heats up as it spirals into the black hole-was blueshifted, meaning the black hole is moving rapidly toward Earth. Meanwhile, the surrounding gas exhibited much weaker blueshift, indicating that the black hole is traveling significantly faster than the rest of its galaxy.

The researchers propose that this ejection resulted from the collision of two galaxies, causing their central black holes to merge into a larger one. This merger would have generated gravitational waves that radiated outward in one direction, while the newly formed black hole recoiled in the opposite direction.

"The evidence for a recoil kick appears strong and, while there is never certainty in astrophysics, this is convincing," says Alessia Gualandris of the University of Surrey, UK.

However, Luke Zoltan Kelley of the University of California, Berkeley, remains cautious. He notes that while this is a promising candidate for a supermassive black hole merger, interpreting light from the region around an SMBH-known as the active galactic nucleus (AGN)-is complex. AGNs can sometimes appear to move quickly even without a merger, so further detailed modeling is needed to confirm the recoil hypothesis.