1,645 research outputs found
Relativistic Collapse of Rotating Supermassive Stars to Supermassive Black Holes
There is compelling evidence that supermassive black holes (SMBHs) exist. Yet
the origin of these objects, or their seeds, is still unknown. We are
performing general relativistic simulations of gravitational collapse to black
holes in different scenarios to help reveal how SMBH seeds might arise in the
universe. SMBHs with ~ 10^9 solar masses must have formed by z > 6, or within
10^9 yrs after the Big Bang, to power quasars. It may be difficult for gas
accretion to build up such a SMBH by this time unless the initial seed black
hole already has a substantial mass. One plausible progenitor of a massive seed
black hole is a supermassive star (SMS). We have followed the collapse of a SMS
to a SMBH by means of 3D hydrodynamic simulations in post-Newtonian gravity and
axisymmetric simulations in full general relativity. The initial SMS of
arbitrary mass M in these simulations rotates uniformly at the mass--shedding
limit and is marginally unstable to radial collapse. The final black hole mass
and spin are determined to be M_h/M ~ 0.9 and J_h/M_h^2 ~ 0.75. The remaining
mass goes into a disk of mass M_{disk}/M ~ 0.1. This disk arises even though
the total spin of the progenitor star, J/M^2 = 0.97, is safely below the Kerr
limit. The collapse generates a mild burst of gravitational radiation.
Nonaxisymmetric bars or one-armed spirals may arise during the quasi-stationary
evolution of a SMS, during its collapse, or in the ambient disk about the hole,
and are potential sources of quasi-periodic waves, detectable by LISA.Comment: 11 pages, to appear in "The Astrophysics of Gravitational Wave
Sources", Proceedings of a Workshop held at the University of Maryland in
April 2003, ed. J. Centrella, AIP, in pres
GRMHD simulations of prompt-collapse neutron star mergers: the absence of jets
Inspiraling and merging binary neutron stars are not only important source of
gravitational waves, but also promising candidates for coincident
electromagnetic counterparts. These systems are thought to be progenitors of
short gamma-ray bursts (sGRBs). We have shown previously that binary neutron
star mergers that undergo {\it delayed} collapse to a black hole surrounded by
a {\it weighty} magnetized accretion disk can drive magnetically-powered jets.
We now perform magnetohydrodynamic simulations in full general relativity of
binary neutron stars mergers that undergo {\it prompt} collapse to explore the
possibility of jet formation from black hole-{\it light} accretion disk
remnants. We find that after ms
[ is the ADM mass] following prompt black hole formation, there is
no evidence of mass outflow or magnetic field collimation. The rapid formation
of the black hole following merger prevents magnetic energy from approaching
force-free values above the magnetic poles, which is required for the launching
of a jet by the usual Blandford--Znajek mechanism. Detection of gravitational
waves in coincidence with sGRBs may provide constraints on the nuclear equation
of state (EOS): the fate of an NSNS merger--delayed or prompt collapse, and
hence the appearance or nonappearance of an sGRB--depends on a critical value
of the total mass of the binary, and this value is sensitive to the EOS.Comment: 11 pages, 6 figures, matches published versio
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