Potential kick velocity distribution of black hole X-ray binaries and implications for natal kicks
Abstract

We use very long baseline interferometry to measure the proper motions of three black hole X-ray binaries (BHXBs). Using these results together with data from the literature and Gaia DR2 to collate the best available constraints on proper motion, parallax, distance, and systemic radial velocity of 16 BHXBs, we determined their three-dimensional Galactocentric orbits. We extended this analysis to estimate the probability distribution for the potential kick velocity (PKV) a BHXB system could have received on formation. Constraining the kicks imparted to BHXBs provides insight into the birth mechanism of black holes (BHs). Kicks also have a significant effect on BH–BH merger rates, merger sites, and binary evolution, and can be responsible for spin–orbit misalignment in BH binary systems. 75 per cent of our systems have potential kicks $\gt 70\, \rm {km\,s^{-1}}$. This suggests that strong kicks and hence spin–orbit misalignment might be common among BHXBs, in agreement with the observed quasi-periodic X-ray variability in their power density spectra. We used a Bayesian hierarchical methodology to analyse the PKV distribution of the BHXB population, and suggest that a unimodal Gaussian model with a mean of 107 $\pm \,\,16\, \rm {km\,s^{-1}}$ is a statistically favourable fit. Such relatively high PKVs would also more »

Authors:
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Publication Date:
NSF-PAR ID:
10121273
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
489
Issue:
3
Page Range or eLocation-ID:
p. 3116-3134
ISSN:
0035-8711
Publisher:
Oxford University Press
We study the long-term orbital evolution of stars around a merging massive or supermassive black hole binary (BHB), taking into account the general relativistic effect induced by the black hole (BH) spin. When the BH spin is significant compared to and misaligned with the binary orbital angular momentum, the orbital axis ($\hat{\boldsymbol {l}}$) of the circumbinary star can undergo significant evolution during the binary orbital decay driven by gravitational radiation. Including the spin effect of the primary (more massive) BH, we find that starting from nearly coplanar orbital orientations, the orbital axes $\hat{\boldsymbol {l}}$ of circumbinary stars preferentially evolve towards the spin direction after the merger of the BHB, regardless of the initial BH spin orientation. Such alignment phenomenon, i.e. small final misalignment angle between $\hat{\boldsymbol {l}}$ and the spin axis of the remnant BH $\hat{\boldsymbol {S}}$, can be understood analytically using the principle of adiabatic invariance. For the BHBs with extremely mass ratio (m2/m1 ≲ 0.01), $\hat{\boldsymbol {l}}$ may experience more complicated evolution as adiabatic invariance breaks down, but the trend of alignment still works reasonably well when the initial binary spin–orbit angle is relatively small. Our result suggests that the correlation between the orientations of stellar orbitsmore »
Making the most of the rapidly increasing population of gravitational-wave detections of black hole (BH) and neutron star (NS) mergers requires comparing observations with population synthesis predictions. In this work, we investigate the combined impact from the key uncertainties in population synthesis modelling of the isolated binary evolution channel: the physical processes in massive binary-star evolution and the star formation history as a function of metallicity, Z, and redshift z, $\mathcal {S}(Z,z)$. Considering these uncertainties, we create 560 different publicly available model realizations and calculate the rate and distribution characteristics of detectable BHBH, BHNS, and NSNS mergers. We find that our stellar evolution and $\mathcal {S}(Z,z)$ variations can combined impact the predicted intrinsic and detectable merger rates by factors in the range 102–104. We find that BHBH rates are dominantly impacted by $\mathcal {S}(Z,z)$ variations, NSNS rates by stellar evolution variations and BHNS rates by both. We then consider the combined impact from all uncertainties considered in this work on the detectable mass distribution shapes (chirp mass, individual masses, and mass ratio). We find that the BHNS mass distributions are predominantly impacted by massive binary-star evolution changes. For BHBH and NSNS, we find that both uncertainties are important. Wemore »