Striking a Chord with Spectral Sirens: Multiple Features in the Compact Binary Population Correlate with H₀

Abstract Spectral siren measurements of the Hubble constant ( H 0 ) rely on correlations between observed detector-frame masses and luminosity distances. Features in the source-frame mass distribution can induce these correlations. It is crucial, then, to understand (i) which features in the source-frame mass distribution are robust against model (re)parameterization, (ii) which features carry the most information about H 0 , and (iii) whether distinct features independently correlate with cosmological parameters. We study these questions using real gravitational-wave observations from the LIGO-Virgo-KAGRA Collaborations' third observing run. Although constraints on H 0 are weak, we find that current data reveals several prominent features in the mass distribution, including peaks in the binary black hole source-frame mass distribution near ∼9 M ⊙ and ∼32 M ⊙ and a roll-off at masses above ∼46 M ⊙. For the first time using real data, we show that all of these features carry cosmological information and that the peak near ∼32 M ⊙ consistently correlates with H 0 most strongly. Introducing model-independent summary statistics, we show that these statistics independently correlate with H 0 , exactly what is required to limit systematics within future spectral siren measurements from the (expected) astrophysical evolution of the mass distribution.