1,000km/second: JWST sees a supersonic supermassive black hole screaming through space

NASA's James Webb Space Telescope has discovered a black hole that was booted out of its galaxy and is now zooming through space at a staggering speed of 1,000 kilometres per second. The runaway supermassive black hole is at least 10 million times the mass of the Sun. It is now the first confirmed runaway supermassive black hole, leaving scientists wondering about the strength of the gravitational kick that caused it to move at such an unimaginable speed through the cosmos. "The forces that are needed to dislodge such a massive black hole from its home are enormous. And yet, it was predicted that such escapes should occur!" team leader Pieter van Dokkum of Yale University told Space.com.

RBH-1, first reported in 2023, comes from a pair of galaxies named the "Cosmic Owl". It is moving at 3,000 times the speed of sound at sea level here on Earth. It has a massive bow shock, the size of an entire galaxy, in front of it, with a star formation extending for 200,000 light-years tailing behind it. What led the black hole to leave its galaxy? The researchers wrote in a preprint uploaded to arXiv that it possibly happened because of gravitational recoil from a supermassive black hole merger.

How did the researchers see the black hole?

The researchers wrote that "the wake is powered by a supersonic runaway supermassive black hole, a long-predicted consequence of gravitational-wave recoil or multi-body ejection from galactic nuclei." Like any other black hole, it also has an event horizon that traps light, making it difficult to see. RBH-"drives a shock wave in the gas that is moving through, and it is this shock wave, and the wake of the shock wave behind the black hole, that we see," van Dokkum said.

As it steers through space, the supermassive black hole pushes the gas sideways "away from the supermassive black hole at a velocity of hundreds of km per second. This dynamical signature was observed with JWST. The black hole likely went rogue as two galaxies merged, and each of their black holes also came together. This gives a "powerful kick to the newly formed black hole" leading it to move at "a speed of 1,000 km/s, enough to eject the black hole."

The three-body interaction is also possible, as one galaxy could have had a pair of binary black holes at its centre. In this scenario, when the third black hole enters the scene, one of them is kicked out. van Dokkum thinks the first reason is more likely in the case of this runaway supermassive black hole.