TY - JOUR
T1 - Remnant Black Hole Kicks and Implications for Hierarchical Mergers
AU - Mahapatra, Parthapratim
AU - Gupta, Anuradha
AU - Favata, Marc
AU - Arun, K. G.
AU - Sathyaprakash, B. S.
N1 - Publisher Copyright:
© 2021. The American Astronomical Society. All rights reserved.
PY - 2021/9/10
Y1 - 2021/9/10
N2 - When binary black holes merge in dense star clusters, their remnants can pair up with other black holes in the cluster, forming heavier and heavier black holes in a process called hierarchical merger. The most important condition for hierarchical merger to occur is that remnants formed by mergers are retained by the host star cluster. Using the publicly available gravitational-wave event database, we infer the magnitudes of kick velocities imparted to the remnant black holes due to anisotropic emission of gravitational waves and use that to quantify the retention probability of each event as a function of the escape speed of the star cluster. Among the second gravitational-wave transient catalog (GWTC-2) events, GW190814 provides the tightest constraint on the kick magnitude with Vkick = 74-7+10 km s-1 at the 90% credible level. We find that star clusters with escape speeds of 200 km s-1 can retain about 50% of the events in the GWTC-2. Using the escape speed distributions of nuclear star clusters and globular clusters, we find that ∼17 (2) remnants of GWTC-2 may be retained by the host star cluster if all GWTC-2 events occurred in nuclear (globular) clusters. Our study demonstrates the importance of folding in kick velocity inferences in future studies of hierarchical mergers.
AB - When binary black holes merge in dense star clusters, their remnants can pair up with other black holes in the cluster, forming heavier and heavier black holes in a process called hierarchical merger. The most important condition for hierarchical merger to occur is that remnants formed by mergers are retained by the host star cluster. Using the publicly available gravitational-wave event database, we infer the magnitudes of kick velocities imparted to the remnant black holes due to anisotropic emission of gravitational waves and use that to quantify the retention probability of each event as a function of the escape speed of the star cluster. Among the second gravitational-wave transient catalog (GWTC-2) events, GW190814 provides the tightest constraint on the kick magnitude with Vkick = 74-7+10 km s-1 at the 90% credible level. We find that star clusters with escape speeds of 200 km s-1 can retain about 50% of the events in the GWTC-2. Using the escape speed distributions of nuclear star clusters and globular clusters, we find that ∼17 (2) remnants of GWTC-2 may be retained by the host star cluster if all GWTC-2 events occurred in nuclear (globular) clusters. Our study demonstrates the importance of folding in kick velocity inferences in future studies of hierarchical mergers.
UR - http://www.scopus.com/inward/record.url?scp=85115365823&partnerID=8YFLogxK
U2 - 10.3847/2041-8213/ac20db
DO - 10.3847/2041-8213/ac20db
M3 - Article
AN - SCOPUS:85115365823
SN - 2041-8205
VL - 918
JO - Astrophysical Journal Letters
JF - Astrophysical Journal Letters
IS - 2
M1 - L31
ER -