Magnetic Braking and Damping of Differential Rotation in Massive Stars. (arXiv:1812.03176v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Sun_L/0/1/0/all/0/1">Lunan Sun</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ruiz_M/0/1/0/all/0/1">Milton Ruiz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shapiro_S/0/1/0/all/0/1">Stuart L. Shapiro</a>
Fragmentation of highly differentially rotating massive stars that undergo
collapse has been suggested as a possible channel for binary black hole
formation. Such a scenario could explain the formation of the new population of
massive black holes detected by the LIGO/VIRGO gravitational wave laser
interferometers. We probe that scenario by performing general relativistic
magnetohydrodynamic simulations of differentially rotating massive stars
supported by thermal radiation pressure domination plus a gas pressure
perturbation. The stars are initially threaded by a dynamically weak, poloidal
magnetic field confined to the stellar interior. We find that magnetic braking
and turbulent viscous damping via magnetic winding and the magnetorotational
instability in the bulk of the star redistribute angular momentum, damp
differential rotation and induce the formation of a massive and nearly
uniformly rotating inner core surrounded by a Keplerian envelope. The core +
disk configuration evolves on a secular timescale and remains in
quasi-stationary equilibrium until the termination of our simulations. Our
results suggest that the high degree of differential rotation required for
$m=2$ seed density perturbations to trigger gas fragmentation and binary black
formation is likely to be suppressed during the normal lifetime of the star
prior to evolving to the point of dynamical instability to collapse. Other
cataclysmic events, such as stellar mergers leading to collapse, may therefore
be necessary to reestablish sufficient differential rotation and density
perturbations to drive nonaxisymmetric modes leading to binary black hole
formation.
Fragmentation of highly differentially rotating massive stars that undergo
collapse has been suggested as a possible channel for binary black hole
formation. Such a scenario could explain the formation of the new population of
massive black holes detected by the LIGO/VIRGO gravitational wave laser
interferometers. We probe that scenario by performing general relativistic
magnetohydrodynamic simulations of differentially rotating massive stars
supported by thermal radiation pressure domination plus a gas pressure
perturbation. The stars are initially threaded by a dynamically weak, poloidal
magnetic field confined to the stellar interior. We find that magnetic braking
and turbulent viscous damping via magnetic winding and the magnetorotational
instability in the bulk of the star redistribute angular momentum, damp
differential rotation and induce the formation of a massive and nearly
uniformly rotating inner core surrounded by a Keplerian envelope. The core +
disk configuration evolves on a secular timescale and remains in
quasi-stationary equilibrium until the termination of our simulations. Our
results suggest that the high degree of differential rotation required for
$m=2$ seed density perturbations to trigger gas fragmentation and binary black
formation is likely to be suppressed during the normal lifetime of the star
prior to evolving to the point of dynamical instability to collapse. Other
cataclysmic events, such as stellar mergers leading to collapse, may therefore
be necessary to reestablish sufficient differential rotation and density
perturbations to drive nonaxisymmetric modes leading to binary black hole
formation.
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