28 research outputs found
Series expansions and sudden singularities
We construct solutions of the Friedmann equations near a sudden singularity
using generalized series expansions for the scale factor, the density, and the
pressure of the fluid content. In this way, we are able to arrive at a solution
with a sudden singularity containing two free constants, as required for a
general solution of the cosmological equations.Comment: 4 pages, contribution for the Proceedings of the MG13 Meeting on
General Relativity, Stockholm, July 201
Numerical method for binary black hole/neutron star initial data: Code test
A new numerical method to construct binary black hole/neutron star initial
data is presented. The method uses three spherical coordinate patches; Two of
these are centered at the binary compact objects and cover a neighborhood of
each object; the third patch extends to the asymptotic region. As in the
Komatsu-Eriguchi-Hachisu method, nonlinear elliptic field equations are
decomposed into a flat space Laplacian and a remaining nonlinear expression
that serves in each iteration as an effective source. The equations are solved
iteratively, integrating a Green's function against the effective source at
each iteration. Detailed convergence tests for the essential part of the code
are performed for a few types of selected Green's functions to treat different
boundary conditions. Numerical computation of the gravitational potential of a
fluid source, and a toy model for a binary black hole field are carefully
calibrated with the analytic solutions to examine accuracy and convergence of
the new code. As an example of the application of the code, an initial data set
for binary black holes in the Isenberg-Wilson-Mathews formulation is presented,
in which the apparent horizons are located using a method described in Appendix
A.Comment: 19 pages, 18 figure
Evolution of equal mass binary bare quark stars in full general relativity: could a supramassive merger remnant experience prompt collapse?
We have evolved mergers of equal-mass binary quark stars, the total mass of which is close to the mass shedding limit of uniformly rotating configurations, in fully general relativistic hydrodynamic simulations, aimed at investigating the post-merger outcomes. In particular, we have identified the threshold mass for prompt black hole formation after the merger, by tracing the minimum lapse function as well as the amount of ejected material during the merger simulation. A semi-analytical investigation based on the angular momentum contained in the merger remnant is also performed to verify the results. For the equation of state considered in this work, the maximum mass of TOV solutions for which is 2.10 , the threshold mass is found between 3.05 and 3.10 . This result is consistent (with a quantitative error smaller than 1%) with the universal relation derived from the numerical results of symmetric binary neutron star mergers. Contrary to the neutron star case, the threshold mass is close to the mass shedding limit of uniformly rotating quark star. Consequently, we have found that binary quark stars with total mass corresponding to the long-lived supramassive remnant for neutron star case, could experience collapse to black hole within several times dynamical timescale, making quark stars as exceptions of the commonly accepted post-merger scenarios for binary neutron star mergers. We have suggested explanation for both the similarity and the difference, between quark stars and neutron stars
Equilibrium solutions of relativistic rotating stars with mixed poloidal and toroidal magnetic fields
Stationary and axisymmetric solutions of relativistic rotating stars with
strong mixed poloidal and toroidal magnetic fields are obtained numerically.
Because of the mixed components of the magnetic field, the underlying
stationary and axisymmetric spacetimes are no longer circular. These
configurations are computed from the full set of the Einstein-Maxwell
equations, Maxwell's equations and from first integrals and integrability
conditions of the magnetohydrodynamic equilibrium equations. After a brief
introduction of the formulation of the problem, we present the first results
for highly deformed magnetized rotating compact stars.Comment: 7 pages, to appear in PRD rapid communicatio
Enabling real-time multi-messenger astrophysics discoveries with deep learning
Multi-messenger astrophysics is a fast-growing, interdisciplinary field that combines data, which vary in volume and speed of data processing, from many different instruments that probe the Universe using different cosmic messengers: electromagnetic waves, cosmic rays, gravitational waves and neutrinos. In this Expert Recommendation, we review the key challenges of real-time observations of gravitational wave sources and their electromagnetic and astroparticle counterparts, and make a number of recommendations to maximize their potential for scientific discovery. These recommendations refer to the design of scalable and computationally efficient machine learning algorithms; the cyber-infrastructure to numerically simulate astrophysical sources, and to process and interpret multi-messenger astrophysics data; the management of gravitational wave detections to trigger real-time alerts for electromagnetic and astroparticle follow-ups; a vision to harness future developments of machine learning and cyber-infrastructure resources to cope with the big-data requirements; and the need to build a community of experts to realize the goals of multi-messenger astrophysics
Waveform Modelling for the Laser Interferometer Space Antenna
LISA, the Laser Interferometer Space Antenna, will usher in a new era in
gravitational-wave astronomy. As the first anticipated space-based
gravitational-wave detector, it will expand our view to the millihertz
gravitational-wave sky, where a spectacular variety of interesting new sources
abound: from millions of ultra-compact binaries in our Galaxy, to mergers of
massive black holes at cosmological distances; from the beginnings of inspirals
that will venture into the ground-based detectors' view to the death spiral of
compact objects into massive black holes, and many sources in between. Central
to realising LISA's discovery potential are waveform models, the theoretical
and phenomenological predictions of the pattern of gravitational waves that
these sources emit. This white paper is presented on behalf of the Waveform
Working Group for the LISA Consortium. It provides a review of the current
state of waveform models for LISA sources, and describes the significant
challenges that must yet be overcome.Comment: 239 pages, 11 figures, white paper from the LISA Consortium Waveform
Working Group, invited for submission to Living Reviews in Relativity,
updated with comments from communit