Abstract Current theoretical models predict a mass gap with a dearth of stellar black holes (BHs) between roughly 50 M ⊙ and 100 M ⊙ , while above the range accessible through massive star evolution, intermediate-mass BHs (IMBHs) still remain elusive. Repeated mergers of binary BHs, detectable via gravitational-wave emission with the current LIGO/Virgo/Kagra interferometers and future detectors such as LISA or the Einstein Telescope, can form both mass-gap BHs and IMBHs. Here we explore the possibility that mass-gap BHs and IMBHs are born as a result of successive BH mergers in dense star clusters. In particular, nuclear star clusters at the centers of galaxies have deep enough potential wells to retain most of the BH merger products after they receive significant recoil kicks due to anisotropic emission of gravitational radiation. Using for the first time simulations that include full stellar evolution, we show that a massive stellar BH seed can easily grow to ∼10 3 –10 4 M ⊙ as a result of repeated mergers with other smaller BHs. We find that lowering the cluster metallicity leads to larger final BH masses. We also show that the growing BH spin tends to decrease in magnitude with the number ofmore »
This content will become publicly available on June 1, 2023
Inferring the Intermediate-mass Black Hole Number Density from Gravitational-wave Lensing Statistics
Abstract The population properties of intermediate-mass black holes remain largely unknown, and understanding their distribution could provide a missing link in the formation of supermassive black holes and galaxies. Gravitational-wave observations can help fill in the gap from stellar mass black holes to supermassive black holes with masses between ∼100–10 4 M ⊙ . In our work, we propose a new method for examining lens populations through lensing statistics of gravitational waves, here focusing on inferring the number density of intermediate-mass black holes through hierarchical Bayesian inference. Simulating ∼200 lensed gravitational-wave signals, we find that existing gravitational-wave observatories at their design sensitivity could either constrain the number density of 10 6 Mpc −3 within a factor of 10, or place an upper bound of ≲10 4 Mpc −3 if the true number density is 10 3 Mpc −3 . More broadly, our method leaves room for incorporation of additional lens populations, providing a general framework for probing the population properties of lenses in the universe.
- Award ID(s):
- 1836814
- Publication Date:
- NSF-PAR ID:
- 10379466
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 932
- Issue:
- 1
- Page Range or eLocation-ID:
- L4
- ISSN:
- 2041-8205
- Sponsoring Org:
- National Science Foundation
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