In a first-of-its-kind measurement, scientists have successfully determined the speed and direction of a newborn black hole that was "kicked" away from its birthplace. The kick, a dramatic consequence of a black hole merger, sent the newly formed black hole hurtling through space at a staggering 112,000 miles per hour (50 kilometers per second). While this isn't the fastest kick ever theorized, it's enough to eject the black hole from its original star cluster.
What is a Black Hole "Kick"?
When two black holes spiral into each other and merge, they release powerful gravitational waves. These waves are ripples in the fabric of spacetime, and if they are emitted asymmetrically—that is, more in one direction than another—they can impart a recoil, or "kick," to the resulting black hole. This is similar to how a gun recoils when a bullet is fired. The kick velocity can be so great that the newborn black hole is launched out of its host galaxy entirely, becoming a "rogue" black hole.
The recent measurement was made by analyzing gravitational wave data from a black hole merger detected in 2019, designated GW190412. By studying the precise signal of the gravitational waves, scientists were able to determine the black hole's three-dimensional motion, a feat previously only theorized.
This video provides a conceptual look at how a gravitational wave kick could launch a black hole from its host galaxy.