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Inferring the pair-instability mass gap from gravitational wave data

Fabio Antonini1, Thomas Callister2, Fani Dosopoulou1, Isobel M. Romero-Shaw3,4,5, and Debatri Chattopadhyay6

  • 1Gravity Exploration Institute, School of Physics and Astronomy, Cardiff University, Cardiff, CF24 3AA, United Kingdom
  • 2Kavli Institute for Cosmological Physics, The University of Chicago, Chicago, Illinois 60637, USA
  • 3DAMTP, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge, CB3 0WA, United Kingdom
  • 4Kavli Institute for Cosmology, Madingley Road, Cambridge, CB3 0HA, United Kingdom
  • 5H. H. Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL, United Kingdom
  • 6Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 1800 Sherman Avenue, Evanston, Illinois 60201, USA

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Phys. Rev. D 112, 063040 – Published 22 September, 2025

DOI: https://doi.org/10.1103/nxnr-pdyx

Abstract

We use hierarchical Bayesian inference with nonparametric Gaussian process models to investigate the effective inspiral spin parameter, χeff, as a function of primary black hole mass in the third gravitational-wave transient catalog (GWTC-3). Our analysis reveals a transition in the population at a primary mass of 46−5+7M⊙. Beyond this mass, the χeff distribution broadens, becomes consistent with being symmetric around zero, and has a median of −0.03−0.59+0.36 (90% credibility). These results are consistent with the presence of a pair-instability mass gap that is repopulated by black holes that are the remnant of a previous merger, formed in dense star clusters. However, asymmetric distributions skewed toward positive χeff are not excluded by current data. Below the inferred transition mass, we constrain the fraction of second-generation black holes to be ≲10%. These results provide model-independent support for a high-mass and high-spin population of black holes in the data, consistent with earlier work using parametric models. Imminent gravitational-wave data releases will be essential to sharpen constraints on spin symmetry and clarify the origin of the black holes.

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Phys. Rev. D 112, 063040– Published 22 September, 2025
  • Received 10 June 2025
  • Accepted 28 August 2025
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