A Baby Black Hole’s Big Kick Through Space
Astronomers have just made a first: they have directly measured the “natal kick” of a newly formed black hole, the recoil velocity it received when born out of the merger of two smaller black holes. The event in question is GW190412, a gravitational wave signal detected in 2019, which involved one black hole about 29.7 times the mass of the Sun merging with another around 8.4 solar masses. Because the two were different sizes and had particular spins, the merger was asymmetric, and the resulting black hole was sent speeding through space. It is hurtling at over 111,600 miles per hour (≈ 179,600 km/h). This measurement marks the first time scientists have used gravitational waves alone to deduce the “kick” imparted to a black hole at formation. By analyzing the waveform’s asymmetry and considering the mass ratio and spins of the merging partners, they could infer how much momentum was left off-center and how that caused a recoil. That kind of motion can be sufficient to kick a blac...