When Are LIGO/Virgo’s Big Black Hole Mergers?

We study the evolution of binary black hole (BBH) mass distribution across cosmic time. The second gravitational-wave transient catalog (GWTC-2) from LIGO/Virgo contains BBH events out to redshifts $z \sim 1$, with component masses in range $\sim5$--$80\,M_\odot$. In this catalog, biggest holes, $m_1 \gtrsim 45\,M_\odot$, are only found at highest redshifts, 0.4$. ask whether absence high-mass observations low redshift indicates that astrophysical evolves: BBHs merge high redshift, and cease merging redshift. Alternatively, feature might be explained by selection effects. Modeling primary spectrum as a power law sharp maximum cutoff (Truncated model), we find increases ($> 99.9\%$ credibility). An abrupt is expected (pulsational) pair instability supernova simulations; however, GWTC-2 consistent Truncated model if location $45^{+13}_{-5}\,M_\odot$ < 0.4$ $80^{+16}_{-13}\,M_\odot$ > has break (Broken law) ${38^{+15}_{-8}\,M_\odot}$, rather than cutoff, data non-evolving distribution. case, overall rate mergers, all masses, increasing Future will confidently distinguish between evolves gradual taper, such Broken law. After $\sim 100$ merger observations, continued high-mass, low-redshift would provide clear signature