Evidence of large recoil velocity from a black hole merger signal

TL;DR

This paper presents the first evidence of a large recoil velocity from a gravitational wave event, GW200129, with implications for black hole dynamics, galaxy evolution, and tests of general relativity.

Contribution

It constrains the recoil velocity of GW200129 using numerical relativity models, demonstrating a significant kick and its astrophysical implications, a novel analysis for an individual GW event.

Findings

Recoil velocity of approximately 1542 km/s with uncertainties.

Less than 0.48% probability of remnant retention in globular clusters.

Kick effects do not bias current tests of general relativity.

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 $v_f \sim 1542^{+747}_{-1098}$ km/s or $v_f \gtrsim 698$ 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.