172 research outputs found
Global simulations of strongly magnetized remnant massive neutron stars formed in binary neutron star mergers
We perform a general-relativistic magnetohydrodynamics simulation for
ms after merger of a binary neutron star to a remnant massive
neutron star (RMNS) with a high spatial resolution of the finest grid
resolution m. First, we estimate that the Kelvin-Helmholtz instability
at merger could amplify the magnetic-field energy up to of the
thermal energy. Second, we find that the magnetorotational instability in the
RMNS envelope and torus with sustains
magneto-turbulent state and the effective viscous parameter in these regions is
likely to converge to -- with respect to the grid
resolution. Third, the current grid resolution is not still fine enough to
sustain magneto-turbulent state in the RMNS with .Comment: 18 pages, 10 figures, PRD in pres
Three dimensional evolution of differentially rotating magnetized neutron stars
We construct a new three-dimensional general relativistic
magnetohydrodynamics code, in which a fixed mesh refinement technique is
implemented. To ensure the divergence-free condition as well as the magnetic
flux conservation, we employ the method by Balsara (2001). Using this new code,
we evolve differentially rotating magnetized neutron stars, and find that a
magnetically driven outflow is launched from the star exhibiting a kink
instability. The matter ejection rate and Poynting flux are still consistent
with our previous finding (Shibata et al., 2011) obtained in axisymmetric
simulations.Comment: 12 pages, 14 figures, accepted by PR
Constraint on the maximum mass of neutron stars using GW170817 event
We revisit the constraint on the maximum mass of cold spherical neutron stars
coming from the observational results of GW170817. We develop a new framework
for the analysis by employing both energy and angular momentum conservation
laws as well as solid results of latest numerical-relativity simulations and of
neutron stars in equilibrium. The new analysis shows that the maximum mass of
cold spherical neutron stars can be only weakly constrained as M_{\rm max}
\alt 2.3M_\odot. Our present result illustrates that the merger remnant
neutron star at the onset of collapse to a black hole is not necessarily
rapidly rotating and shows that we have to take into account the angular
momentum conservation law to impose the constraint on the maximum mass of
neutron stars.Comment: 14 pages, 5 figures, matches the version accepted by PRD for
publicatio
Truncated Moment Formalism for Radiation Hydrodynamics in Numerical Relativity
A truncated moment formalism for general relativistic radiation
hydrodynamics, based on the Thorne's moment formalism, is derived. The fluid
rest frame is chosen to be the fiducial frame for defining the radiation
moments. Then, zeroth-, first-, and second-rank radiation moments are defined
from the distribution function with a physically reasonable assumption for it
in the optically thin and thick limits. The source terms are written, focusing
specifically on the neutrino transfer and neglecting higher harmonic angular
dependence of the reaction angle. Finally, basic equations for a truncated
moment formalism for general relativistic radiation hydrodynamics in a closed
covariant form are derived assuming a closure relation among the radiation
stress tensor, energy density, and energy flux, and a variable Eddington
factor, which works well.Comment: 33 pages, 2 figures, to be published in Prog. Theor. Phy
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