The James Webb Space Telescope (JWST) has confirmed the existence of a runaway supermassive black hole, a phenomenon that has long intrigued astronomers. This black hole, named RBH-1, is at least 10 million times the mass of the Sun and is traveling at an astonishing 954 kilometers per second, or 0.32% of the speed of light, through the circumgalactic medium. While it's not the fastest stellar object ever observed, the sheer force required to propel a black hole of that mass at such a velocity is mind-boggling.
RBH-1 was first reported in 2023, and follow-up observations using JWST's NIRSpec instrument have now confirmed its status as a runaway. The black hole is located at a light travel time of 7.5 billion years, with a bow shock and a trail of star formation extending for 200,000 light-years behind it. The clues initially pointed to a clear picture of a runaway, and the new observations have solidified this conclusion.
The researchers believe that the gravitational recoil from a supermassive black hole merger is the likely cause of RBH-1's acceleration. As galaxies assemble and grow around black holes, mergers can occur, leading to the release of gravitational energy and the potential for black holes to be ejected from their host galaxies. This mechanism has been supported by evidence of multiple candidate runaway supermassive black holes, a galaxy with a second supermassive black hole at its outskirts, and even a galaxy that appears to be missing its supermassive black hole.
Simulations suggest that there could be a significant number of rogue supermassive black holes out there, lurking in the darkness of intergalactic space. The velocity distribution across the bow shock in front of RBH-1 was mapped using JWST, revealing a blueshift and a dramatic, abrupt velocity difference between the material in front and behind the shock front. This structure can only be created by a high-speed, massive object moving at around 954 kilometers per second.
The researchers propose that the mechanism behind RBH-1's acceleration is a three-body gravitational interaction between three supermassive black holes, brought together by galaxy mergers. However, with more accurate measurements, they now believe that the most likely explanation is a merger between two supermassive black holes that came together after their host galaxies merged. As they merged, the asymmetrical release of gravitational energy imparted a recoil kick, sending the newly formed black hole flying.
The measured velocity of RBH-1 and the mass of the galaxy it left behind are consistent with models of this process. The researchers have named the object RBH-1, recognizing it as the first confirmed runaway supermassive black hole. This discovery is a significant validation of a 50-year-old prediction that supermassive black holes can escape their host galaxies through gravitational wave recoil or three-body interactions.
