On the Origin of GW190521-like Events from Repeated Black Hole Mergers in Star Clusters
Abstract
LIGO and Virgo have reported the detection of GW190521, from the merger of a binary black hole (BBH) with a total mass around 150 M⊙. While current stellar models limit the mass of any black hole (BH) remnant to about 40-50 M⊙, more massive BHs can be produced dynamically through repeated mergers in the core of a dense star cluster. The process is limited by the recoil kick (due to anisotropic emission of gravitational radiation) imparted to merger remnants, which can escape the parent cluster, thereby terminating growth. We study the role of the host cluster metallicity and escape speed in the buildup of massive BHs through repeated mergers. Almost independent of host metallicity, we find that a BBH of about 150 M⊙ could be formed dynamically in any star cluster with escape speed ≳200 km s-1, as found in galactic nuclear star clusters as well as the most massive globular clusters and super star clusters. Using an inspiral-only waveform, we compute the detection probability for different primary masses (≥60 M⊙) as a function of secondary mass and find that the detection probability increases with secondary mass and decreases for larger primary mass and redshift. Future additional detections of massive BBH mergers will be of fundamental importance for understanding the growth of massive BHs through dynamics and the formation of intermediate-mass BHs.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2020
- DOI:
- 10.3847/2041-8213/abbc0a
- arXiv:
- arXiv:2009.05065
- Bibcode:
- 2020ApJ...902L..26F
- Keywords:
-
- Gravitational waves;
- Gravitational wave sources;
- Gravitational wave detectors;
- Gravitational wave astronomy;
- Astrophysical black holes;
- Black holes;
- Intermediate-mass black holes;
- Black hole physics;
- Globular star clusters;
- Open star clusters;
- Star clusters;
- Superclusters;
- 678;
- 677;
- 676;
- 675;
- 98;
- 162;
- 816;
- 159;
- 656;
- 1160;
- 1567;
- 1657;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 8 pages, 5 figures, accepted by ApJ Lett