Black hole, neutron star, and white dwarf merger rates in AGN discs
ABSTRACT Advanced LIGO and Advanced Virgo are detecting a large number of binary stellar origin black hole (BH) mergers. A promising channel for accelerated BH merger lies in active galactic nucleus (AGN) discs of gas around supermasssive BHs. Here, we investigate the relative number of compact object (CO) mergers in AGN disc models, including BH, neutron stars (NS), and white dwarfs, via Monte Carlo simulations. We find the number of all merger types in the bulk disc grows ∝ t1/3 which is driven by the Hill sphere of the more massive merger component. Median mass ratios of NS–BH mergers in AGN discs are $\tilde{q}=0.07\pm 0.06(0.14\pm 0.07)$ for mass functions (MF) M−1(− 2). If a fraction fAGN of the observed rate of BH–BH mergers (RBH–BH) come from AGN, the rate of NS–BH (NS–NS) mergers in the AGN channel is ${R}_{\mathrm{ BH}\!-\!\mathrm{ NS}} \sim f_{\mathrm{ AGN}}[10,300]\, \rm {Gpc}^{-3}\, \rm {yr}^{-1},({\mathit{ R}}_{NS\!-\!NS} \le \mathit{ f}_{AGN}400\, \rm {Gpc}^{-3}\, \rm {yr}^{-1}$). Given the ratio of NS–NS/BH–BH LIGO search volumes, from preliminary O3 results the AGN channel is not the dominant contribution to observed NS–NS mergers. The number of lower mass gap events expected is a strong function of the nuclear MF and mass segregation efficiency. CO merger ratios more »
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Award ID(s):
Publication Date:
NSF-PAR ID:
10230599
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
498
Issue:
3
Page Range or eLocation-ID:
4088 to 4094
ISSN:
0035-8711
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