45 research outputs found
Maximal Slicing for Puncture Evolutions of Schwarzschild and Reissner-Nordstr\"om Black Holes
We prove by explicit construction that there exists a maximal slicing of the
Schwarzschild spacetime such that the lapse has zero gradient at the puncture.
This boundary condition has been observed to hold in numerical evolutions, but
in the past it was not clear whether the numerically obtained maximal slices
exist analytically. We show that our analytical result agrees with numerical
simulation. Given the analytical form for the lapse, we can derive that at late
times the value of the lapse at the event horizon approaches the value
, justifying the numerical estimate of 0.3 that
has been used for black hole excision in numerical simulations. We present our
results for the non-extremal Reissner-Nordstr\"om metric, generalizing previous
constructions of maximal slices.Comment: 21 pages, 9 figures, published version with changes to Sec. VI
A simple construction of initial data for multiple black holes
We consider the initial data problem for several black holes in vacuum with
arbitrary momenta and spins on a three space with punctures. We compactify the
internal asymptotically flat regions to obtain a computational domain without
inner boundaries. When treated numerically, this leads to a significant
simplification over the conventional approach which is based on throats and
isometry conditions. In this new setting it is possible to obtain existence and
uniqueness of solutions to the Hamiltonian constraint.Comment: 4 pages, LaTeX (RevTeX), minor changes, improved presentation, to
appear in PR
Numerical relativity simulations of binary neutron stars
We present a new numerical relativity code designed for simulations of
compact binaries involving matter. The code is an upgrade of the BAM code to
include general relativistic hydrodynamics and implements state-of-the-art
high-resolution-shock-capturing schemes on a hierarchy of mesh refined
Cartesian grids with moving boxes. We test and validate the code in a series of
standard experiments involving single neutron star spacetimes. We present test
evolutions of quasi-equilibrium equal-mass irrotational binary neutron star
configurations in quasi-circular orbits which describe the late inspiral to
merger phases. Neutron star matter is modeled as a zero-temperature fluid;
thermal effects can be included by means of a simple ideal-gas prescription. We
analyze the impact that the use of different values of damping parameter in the
Gamma-driver shift condition has on the dynamics of the system. The use of
different reconstruction schemes and their impact in the post-merger dynamics
is investigated. We compute and characterize the gravitational radiation
emitted by the system. Self-convergence of the waves is tested, and we
consistently estimate error-bars on the numerically generated waveforms in the
inspiral phase