Constraints on the binary black hole hypothesis for system LB-1. (arXiv:1911.12581v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Shen_R/0/1/0/all/0/1">R.-F. Shen</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Matzner_C/0/1/0/all/0/1">C. D. Matzner</a> (2), <a href="http://arxiv.org/find/astro-ph/1/au:+Howard_A/0/1/0/all/0/1">A. W. Howard</a> (3), <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_W/0/1/0/all/0/1">W. Zhang</a> (4) ((1) SYSU, (2) U of Toronto, (3) Caltech, (4) NAOC)
At about 70 solar masses, the recently-discovered dark object orbited by a
B-type star in the system LB-1 is difficult to understand as the end point of
standard stellar evolution, except as a binary black hole (BBH). LB-1 shows a
strong, broad H-alpha emission line that is best attributed to a gaseous disk
surrounding the dark mass. We use the observed H-alpha line shape, particularly
its wing extension, to constrain the inner radius of the disk and thereby the
separation of a putative BBH. The hypothesis of a current BBH is effectively
ruled out on the grounds that its merger time must be a small fraction of the
current age of the B star. The hypothesis of a previous BBH that merged to
create the current dark mass is also effectively ruled out by the low orbital
eccentricity, due to the combination of mass loss and kick resulted from
gravitational wave emission in any past merger. We conclude that the current
dark mass is a single black hole produced by the highly mass-conserving,
monolithic collapse of a massive star.
At about 70 solar masses, the recently-discovered dark object orbited by a
B-type star in the system LB-1 is difficult to understand as the end point of
standard stellar evolution, except as a binary black hole (BBH). LB-1 shows a
strong, broad H-alpha emission line that is best attributed to a gaseous disk
surrounding the dark mass. We use the observed H-alpha line shape, particularly
its wing extension, to constrain the inner radius of the disk and thereby the
separation of a putative BBH. The hypothesis of a current BBH is effectively
ruled out on the grounds that its merger time must be a small fraction of the
current age of the B star. The hypothesis of a previous BBH that merged to
create the current dark mass is also effectively ruled out by the low orbital
eccentricity, due to the combination of mass loss and kick resulted from
gravitational wave emission in any past merger. We conclude that the current
dark mass is a single black hole produced by the highly mass-conserving,
monolithic collapse of a massive star.
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