The black hole (BH) masses measured from gravitational wave observations appear to cluster around specific mass values. Consequently, the primary (and chirp) mass distribution of binary black holes (BBHs) inferred using these measurements shows four emerging peaks. These peaks are approximately located at a primary (chirp) mass value of 10 $\, \mathrm{M}_\odot$ (8$\, \mathrm{M}_\odot$), 20 $\, \mathrm{M}_\odot$ (14 $\, \mathrm{M}_\odot$), 35 $\, \mathrm{M}_\odot$ (28 $\, \mathrm{M}_\odot$), and 63 $\, \mathrm{M}_\odot$ (49 $\, \mathrm{M}_\odot$). Although the presence of the first and third peaks has been attributed to BBH formation in star clusters or due to the evolution of stellar binaries in isolation, the second peak has received relatively less attention because it lacks significance in the primary mass distribution. In this article, we report that confidence in the second peak depends on the mass parameter we choose to model the population on. Unlike primary mass, this peak is significant when modelled on the chirp mass. We discuss the disparity as a consequence of mass asymmetry in the observations that cluster at the second peak. Finally, we report this asymmetry as part of a potential trend in the mass ratio distribution manifested as a function of the chirp mass, but not as a function of primary mass, when we include the observation GW190814 in our modelling. The chirp mass is not a parameter of astrophysical relevance. Features present in the chirp mass, but not in the primary mass, are relatively difficult to explain and expected to garner significant interest.
Current observations of binary black hole (BBH) merger events show support for a feature in the primary BH-mass distribution at $\sim \, 35 \ \mathrm{M}_{\odot }$, previously interpreted as a signature of pulsational pair-instability supernovae (PPISNe). Such supernovae are expected to map a wide range of pre-supernova carbon–oxygen (CO) core masses to a narrow range of BH masses, producing a peak in the BH mass distribution. However, recent numerical simulations place the mass location of this peak above $50 \ \mathrm{M}_{\odot }$. Motivated by uncertainties in the progenitor’s evolution and explosion mechanism, we explore how modifying the distribution of BH masses resulting from PPISN affects the populations of gravitational-wave (GW) and electromagnetic (EM) transients. To this end, we simulate populations of isolated BBH systems and combine them with cosmic star formation rates. Our results are the first cosmological BBH-merger predictions made using the binary_c rapid population synthesis framework. We find that our fiducial model does not match the observed GW peak. We can only explain the $35 \ \mathrm{M}_{\odot }$ peak with PPISNe by shifting the expected CO core-mass range for PPISN downwards by $\sim {}15 \ \mathrm{M}_{\odot }$. Apart from being in tension with state-of-the art stellar models, we also find that this is likely in tension with the observed rate of hydrogen-less super-luminous supernovae. Conversely, shifting the mass range upward, based on recent stellar models, leads to a predicted third peak in the BH mass function at $\sim {}64 \ \mathrm{M}_{\odot }$. Thus we conclude that the $\sim {}35 \ \mathrm{M}_{\odot }$ feature is unlikely to be related to PPISN.
more » « less- NSF-PAR ID:
- 10469609
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 526
- Issue:
- 3
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 4130-4147
- Size(s):
- ["p. 4130-4147"]
- Sponsoring Org:
- National Science Foundation
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