Kavli Affiliate: Salvatore Vitale
| First 5 Authors: Salvatore Vitale, Matthew Mould, , ,
| Summary:
Measuring the distribution of spin tilts-the angles between the spin vectors
and the binary orbital angular momentum-in stellar-mass binary black holes
detected by LIGO-Virgo-KAGRA would provide valuable insight into their
astrophysical origins. Analyses of the 69 binary black holes detected through
LIGO-Virgo-KAGRA’s third observing run yielded model-dependent conclusions,
particularly regarding whether the spin tilt distribution exhibits a peak near
alignment, as expected for binaries formed in galactic fields. In this work, we
simulate populations of up to 1500 binary black hole systems with parameters
consistent with the default GWTC-3 analysis, while introducing a correlation
that favors small spin tilts for binaries with mass ratios near unity. We find
that: (a) spurious peaks away from perfect alignment are possible even with
catalogs of up to 300 sources; (b) establishing a definitive peak at alignment
remains difficult even with 1500 detections; (c) integrated measurements —
such as the fraction of events with tilt angles smaller than $10^circ$ or
greater than $90^circ$ — are more robust and should be preferred, achieving
relative $90%$ credible uncertainties of $sim20%-80%$ with 1500 sources;
and (d) even with the largest simulated catalogs, evidence for a mass
ratio-tilt correlation remains inconclusive. Our results suggest that
identifying the formation channels of merging black holes using spin tilts will
remain challenging, but that model-independent measurements may yield more
informative insights over model parameters themselves.
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