Two of a Kind: Comparing big and small black holes in binaries with gravitational waves

Kavli Affiliate: Daniel E. Holz

| First 5 Authors: Amanda M. Farah, Maya Fishbach, Daniel E. Holz, ,

| Summary:

When modeling the population of merging binary black holes, analyses have
generally focused on characterizing the distribution of primary (i.e. more
massive) black holes in the binary, while simplistic prescriptions are used for
the distribution of secondary masses. However, the secondary mass distribution
and its relationship to the primary mass distribution provide a fundamental
observational constraint on the formation history of coalescing binary black
holes. If both black holes experience similar stellar evolutionary processes
prior to collapse, as might be expected in dynamical formation channels, the
primary and secondary mass distributions would show similar features. If they
follow distinct evolutionary pathways (for example, due to binary interactions
that break symmetry between the initially more massive and less massive star),
their mass distributions may differ. We present the first analysis of the
binary black hole population that explicitly fits for the secondary mass
distribution. We find that the data is consistent with a $sim30,M_{odot}$
peak existing only in the distribution of emph{secondary} rather than primary
masses. This would have major implications for our understanding of the
formation of these binaries. Alternatively, the data is consistent with the
peak existing in both component mass distributions, a possibility not included
in most other previous studies. In either case, the peak is observed at
$31.4_{-2.6}^{+2.3},M_{odot}$, which is shifted lower than the value obtained
in previous analyses of the marginal primary mass distribution, placing this
feature in further tension with expectations from a pulsational
pair-instability supernova pileup.

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