What Will Be the Effective Spin Of The Equal And Unequal Mass Black Hole Binaries? (Cosmology)

Thomas Callister and his collaborators found that unequal mass binary black hole mergers have larger effective spins

An increasing number of gravitational wave detection by LIGO/VIRGO observatories not only enable the discovery of binary black hole (BBH) mergers at an ever accelerating pace, but also, it has offered an increasingly clear picture of their mass, spin and redshift distributions. If we want to fully understand the formation and evolution of binary black holes not only just the characterization of these marginal distributions will require but also, the correlations between parameters will be particularly valuable.

Now, Thomas Callister and his collaborators have presented evidence for an intrinsic anti-correlation between the effective inspiral spins and mass ratios of detected BBH mergers.

© Thomas Callister et al.

Under a hierarchical analysis of the Binary Black Hole (BBH) population using Advanced LIGO and Virgo’s GWTC-2 catalog, they found that equal-mass binaries preferentially exhibit a narrow effective spins, while unequal mass binaries exhibit larger effective spins.

This anti-correlation is unexpected because it typically act in an opposite sense to the trend they observationally identified in the data.

“It will be valuable to re-evaluate our understanding of BBH formation in light of the results we presented, exploring which formation channel (or combination of channels) can accommodate the observed trend in mass ratios and effective inspiral spins. If confirmed to be astrophysical, the anti-correlated mass ratios and effective spins of BBHs may offer a firm observational foothold on our path towards understanding the origin of black hole mergers.

— concluded authors of the study

Reference: Thomas A. Callister, Carl-Johan Haster, Ken K. Y. Ng, Salvatore Vitale, Will M. Farr, “Who Ordered That? Unequal-Mass Binary Black Hole Mergers Have Larger Effective Spins”, Arxiv, pp. 1-21, 2021. https://arxiv.org/abs/2106.00521

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