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Exploring the Spin Distribution of Stellar Mass Black Holes

Presentation #110.56 in the session “Stellar/Compact (Poster)”.

Published onApr 01, 2022
Exploring the Spin Distribution of Stellar Mass Black Holes

Based on the Binary Black Hole (BBH) mergers reported in the third Gravitational Wave Transient Catalog (GWTC-3), the distribution of pre-merger black hole (BH) spins peaks near a low value of 0.2, while the distribution of spin-orbit misalignment angles peaks at alignment, but also allows for an isotropic orientation of the component spins (LIGO Scientific Collaboration et al. 2021). Still, the full potential of spin measurements from gravitational wave measurements cannot be achieved due to (1) a degeneracy between the mass ratio in the binary and a combination of the spins of the black holes, and (2) a second degeneracy between between the two spins themselves, which makes it difficult to measure individual spins (Purrer et al. 2016). In addition, the posterior probability distributions for BH spin measurements based on GW measurements are correlated with the assumed prior distributions (Vitale et al. 2017; Abbott et al. 2019, 2020). As there is yet no evidence of a correlation between the spin of a black hole and its mass among the BHs in GWTC-3, comparing the spins of BHs in BBH systems to those of BHs in X-ray binaries (XB) is the most pragmatic way forward, and it can shine light on the formation mechanism of BBHs and provide informative priors for future GW analysis.

The current distribution of BH spins in XBs favors high spins, being inconsistent with the BBH spin distribution at >99.9% level (Fishbach & Kalogera et al. 2021). Still, old spin measurements of BHs in XBs made through the two main methods, continuum fitting and relativistic reflection, do not always agree. Nowadays, in the era of NuSTAR, and with the advancement of numerical models, spin measurements using relativistic reflection are more accurate than ever. In order to be able to compare the spin distributions of the two populations of stellar mass BHs, a uniform treatment of the BH spin measurements in XBs is needed. Additionally, it is crucial to account for possible observational biases in the derived spin distribution. Our analysis aims to address these issues with the distribution of BH spins in XBs in order to produce a meaningful sample of size comparable to that obtained from GW measurements. Further understanding the distribution of BH spins will also help explain the origin and evolution of XB and BBH, massive star evolution, supernovae explosions, the processes that govern black hole formation, and the physics of accretion disk.

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