Magnetorotational collapse of very massive stars to black holes in full general relativity

Journal Article · Mon Oct 15 04:00:00 EDT 2007 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.76.084017· OSTI ID:21032464

Liu, Y T; Shapiro, Stuart L; Stephens, Branson C ^[1]

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1. Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

We perform axisymmetric simulations of the magnetorotational collapse of very massive stars in full general relativity. Our simulations are applicable to the collapse of supermassive stars with masses M > or approx. 10{sup 3}M{sub {center_dot}} and to very massive Population III stars. We model our initial configurations by n=3 polytropes, uniformly rotating near the mass-shedding limit and at the onset of radial instability to collapse. The ratio of magnetic to rotational kinetic energy in these configurations is chosen to be small (1% and 10%). We find that such magnetic fields do not affect the initial collapse significantly. The core collapses to a black hole, after which black-hole excision is employed to continue the evolution long enough for the hole to reach a quasistationary state. We find that the black-hole mass is M{sub h}=0.95M and its spin parameter is J{sub h}/M{sub h}{sup 2}=0.7, with the remaining matter forming a torus around the black hole. The subsequent evolution of the torus depends on the strength of the magnetic field. We freeze the spacetime metric ('Cowling approximation') and continue to follow the evolution of the torus after the black hole has relaxed to quasistationary equilibrium. In the absence of magnetic fields, the torus settles down following ejection of a small amount of matter due to shock heating. When magnetic fields are present, the field lines gradually collimate along the hole's rotation axis. MHD shocks and the magnetorotational instability generate MHD turbulence in the torus and stochastic accretion onto the central black hole. When the magnetic field is strong, a wind is generated in the torus, and the torus undergoes radial oscillations that drive episodic accretion onto the hole. These oscillations produce long-wavelength gravitational waves potentially detectable by the Laser Interferometer Space Antenna. The final state of the magnetorotational collapse always consists of a central black hole surrounded by a collimated magnetic field and a hot, thick accretion torus. This system is a viable candidate for the central engine of a long-soft gamma-ray burst.

• OSTI ID: 21032464
• Journal Information: Physical Review. D, Particles Fields, Journal Name: Physical Review. D, Particles Fields Journal Issue: 8 Vol. 76; ISSN PRVDAQ; ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ANTENNAS
APPROXIMATIONS
AXIAL SYMMETRY
BLACK HOLES
COMPUTERIZED SIMULATION
COSMIC GAMMA BURSTS
COSMOLOGY
GENERAL RELATIVITY THEORY
GRAVITATIONAL WAVES
KINETIC ENERGY
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
MASS
SHOCK HEATING
SPACE-TIME
STOCHASTIC PROCESSES
SUPERMASSIVE STARS
TURBULENCE