Globular cluster formation histories, masses, and radii inferred from gravitational waves

Maya Fishbach*, Giacomo Fragione

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

Globular clusters (GCs) are found in all types of galaxies and harbour some of the most extreme stellar systems, including black holes that may dynamically assemble into merging binary black holes (BBHs). Uncertain GC properties, including when they formed, their initial masses and sizes, affect their production rate of BBH mergers. Using the gravitational-wave transient catalogue (GWTC-3), we measure that dynamically assembled BBHs - those that are consistent with isotropic spin directions - make up 61+29−44% of the total merger rate, with a local merger rate of 10.9+16.8−9.3 Gpc−3 yr−1 rising to 58.9+149.4−46.0 Gpc−3 yr−1 at z = 1. We assume that this inferred rate describes the contribution from GCs and compare it against the Cluster Monte Carlo (CMC) simulation catalogue to directly fit for the GC initial mass function, virial radius distribution, and formation history. We find that GC initial masses are consistent with a Schechter function with slope βm = −1.9+0.8−0.8. Assuming a mass function slope of βm = −2 and a mass range between 104-108 M, we infer a GC formation rate at z = 2 of 5.0+9.4−4.0 Gpc−3 yr−1, or 2.1+3.9−1.7 × 106 M Gpc−3 yr−1 in terms of mass density. We find that the GC formation rate probably rises more steeply than the global star formation rate between z = 0 and z = 3 (82 per cent credibility) and implies a local number density that is fev = 22.6+29.29−16.2 times higher than the observed density of survived GCs. This is consistent with expectations for cluster evaporation, but may suggest that other environments contribute to the rate of BBH mergers with significantly tilted spins.

Original languageEnglish (US)
Pages (from-to)5546-5557
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Volume522
Issue number4
DOIs
StatePublished - Jul 1 2023

Keywords

  • globular clusters: general
  • gravitational waves
  • stars: black holes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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