Observation of a runaway black hole

12. Mai 2022

The final black hole in a binary black-hole merger can attain a recoil velocity, or a "kick", that can reach values up to 5000 km/s, large enough to be ejected from any galaxy. The authors find the first evidence for a large kick from a gravitational-wave signal, with a velocity of ~1500 km/s (90% uncertainty of ~900 km/s). The gravitational-wave signal, GW200129, was observed by the detectors LIGO and Virgo during their third observing run. In this work, the authors reanalyzed the signal using cutting edge gravitational-wave and kick models, which led to the kick measurement. While candidates for recoiling black-holes have been identified from electromagnetic observations, their nature is still debated. Therefore, this marks the first confident observation of a recoiling black hole. Kicks have far-reaching implications for the fields of gravitational-wave astronomy, black-hole formation, galaxy evolution, and tests of general relativity. For example, kick measurements like this are a crucial missing piece of the puzzle behind the origin of the high-mass black holes that have been observed by LIGO and Virgo. As gravitational-wave astronomy matures, the method will enable routine measurements of kicks, providing a previously inaccessible observable for black-hole astrophysics.

Paper abstract

The final black hole left behind after a binary black hole merger can attain a recoil velocity, or a "kick", reaching values up to 5000 km/s. This phenomenon has important implications for gravitational wave astronomy, black hole formation scenarios, testing general relativity, and galaxy evolution. We consider the gravitational wave signal from the binary black hole merger GW200129_065458 (henceforth referred to as GW200129), which has been shown to exhibit strong evidence of orbital precession. Using numerical relativity surrogate models, we constrain the kick velocity of GW200129 to vf ∼ 1542+747−1098 km/s or vf ≳ 698 km/s (one-sided limit), at 90% credibility. This marks the first identification of a large kick velocity for an individual gravitational wave event. Given the kick velocity of GW200129, we estimate that there is a less than 0.48% (7.7%) probability that the remnant black hole after the merger would be retained by globular (nuclear star) clusters. Finally, we show that kick effects are not expected to cause biases in ringdown tests of general relativity for this event, although this may change in the future with improved detectors.

Visualization of the binary black hole merger GW200129, for its maximum likelihood parameters. The binary has a substantial spin in the orbital plane, which causes the orbital plane to precess. This modulates the gravitational wave signal and leads to the large kick after the merger.<br />See https://vijayvarma392.github.io/GW200129/ for further details.

GW200129

Visualization of the binary black hole merger GW200129, for its maximum likelihood parameters. The binary has a substantial spin in the orbital plane, which causes the orbital plane to precess. This modulates the gravitational wave signal and leads to the large kick after the merger.
See https://vijayvarma392.github.io/GW200129/ for further details.
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