Hierarchical mergers of stellar-mass black holes and their gravitational-wave signatures
By Davide Gerosa, Maya Fishbach. Nature Astronomy, 2021
203 citations recorded by the source corpus.
While most of the compact-binary mergers detected by LIGO and Virgo are expected to consist of first-generation black holes formed from the collapse of stars, others might instead be of second (or higher) generation, containing the remnants of previous black-hole mergers. We review theoretical findings, astrophysical modelling and current gravitational-wave evidence of hierarchical stellar-mass black-hole mergers. Such a subpopulation of hierarchically assembled black holes presents distinctive gravitational-wave signatures, namely higher masses, possibly within the pair-instability mass gap, and dimensionless spins clustered at the characteristic value of ~0.7. To produce hierarchical mergers, astrophysical environments need to overcome the relativistic recoils imparted to black-hole merger remnants, a condition that prefers hosts with escape speeds of ≳100 km s−1. Promising locations for efficient production of hierarchical mergers include nuclear star clusters and accretion disks surrounding active galactic nuclei, though environments that are less efficient at retaining merger products such as globular clusters may still contribute significantly to the detectable population of repeated mergers. While GW190521 is the single most promising hierarchical-merger candidate to date, constraints from large population analyses are becoming increasingly more powerful. Theoretical findings and current gravitational-wave evidence of hierarchical stellar-mass black-hole mergers are reviewed. Promising locations for the production of such systems include nuclear star clusters, accretion disks in active galactic nuclei, and potentially globular clusters.
Subfields: Astronomy and Astrophysics, Atmospheric Science
View Paper: https://www.semanticscholar.org/paper/7ad9a9d68494abd6f977813f5c0646f1d5d22c55
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Citations in the corpus
- GW231123: A Binary Black Hole Merger with Total Mass 190–265 M⊙ (2025, unknown): “The scenarios with the highest probability require a formation channel that popu-lates the mass gap, such as prior stellar (e.g., Di Carlo et al. 2020; Renzo et al. 2020a; Kremer et al. 2020) or black-hole (Gerosa & Fishbach 2021) mergers.”
- GWTC-2.1: Deep extended catalog of compact binary coalescences observed by LIGO and Virgo during the first half of the third observing run (2021, background): “[254] Davide Gerosa and Maya Fishbach, “Hierarchical mergers of stellar-mass black holes and their gravitationalwave signatures,” Nature Astronomy 5, 749–760 (2021).”
- 4-OGC: Catalog of Gravitational Waves from Compact Binary Mergers (2021, background): “…such as GW190521 with total mass ∼150Me (Abbott et al. 2020c; Capano et al. 2021), are beginning to constrain formation scenarios (Abbott et al. 2020d; Edelman et al. 2021; Gerosa & Fishbach 2021; Zevin et al. 2021) and deviations from general relativity (Abbott et al. 2021e; Wang et al. 2022).”
- Rates of compact object coalescences (2021, background): “What fraction of merger products avoid being ejected by gravitational-wave recoil kicks and can be reused for subsequent hierarchical mergers (Rodriguez et al., 2018; Gerosa and Fishbach, 2021)?”