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GWTC-4.0: Population Properties of Merging Compact Binaries
A. G. Abac et al 2026 The Astrophysical Journal Letters 1005 .
Caption: Figure 1.
The complete mass spectrum, inferred using the strongly modeled FULLPOP-4.0 and weakly modeled BGP analyses. In the lower triangle of the m1–m2 plane (where m1 > m2 by definition), we show median merger rate density across primary and secondary masses. At m2 = 5 M⊙, the FULLPOP-4.0 model transitions to an alternative pairing function to allow for NSBHs, hence the discontinuity at m2 = 5 M⊙. In the upper triangle we show the fractional uncertainty in the merger rate reflected across the diagonal. The fractional uncertainty ﹩{{\rm{\Delta }}}{ \mathcal R }/{ \mathcal R }﹩ is the difference of the 95th and 5th percentile values divided by the median merger rate. Both the FULLPOP-4.0 and BGP models show similar broad features: a population of BNSs at primary and secondary masses ≲2 M⊙, a population of NSBHs at primary mass ∼9 M⊙ and secondary mass ≲2 M⊙, and finally the population of BBHs with primary and secondary masses ≳9 M⊙. The uncertainties are the smallest in the ∼9 M⊙ and ∼30 M⊙ BBH peaks.
© 2026. The Author(s). Published by the American Astronomical Society.