137 research outputs found
Hydrodynamics of Neutron Star Mergers
The final burst of gravitational radiation emitted by coalescing binary
neutron stars carries direct information about the neutron star fluid, and, in
particular, about the equation of state of nuclear matter at extreme densities.
The final merger may also be accompanied by a detectable electromagnetic
signal, such as a gamma-ray burst. In this paper, we summarize the results of
theoretical work done over the past decade that has led to a detailed
understanding of this hydrodynamic merger process for two neutron stars, and we
discuss the prospects for the detection and physical interpretation of the
gravity wave signals by ground-based interferometers such as LIGO. We also
present results from our latest post-Newtonian SPH calculations of binary
neutron star coalescence, using up to 10^6 SPH particles to compute with higher
spatial resolution than ever before the merger of an initially irrotational
system. We discuss the detectability of our calculated gravity wave signals
based on power spectra.Comment: 13 pages, 5 figures, to appear in "Astrophysical Sources of
Gravitational Radiation", edited by J. M. Centrella (AIP Press
Tidal Interactions and Disruptions of Giant Planets on Highly Eccentric Orbits
We calculate the evolution of planets undergoing a strong tidal encounter
using smoothed particle hydrodynamics (SPH), for a range of periastron
separations. We find that outside the Roche limit, the evolution of the planet
is well-described by the standard model of linear, non-radial, adiabatic
oscillations. If the planet passes within the Roche limit at periastron,
however, mass can be stripped from it, but in no case do we find enough energy
transferred to the planet to lead to complete disruption. In light of the three
new extrasolar planets discovered with periods shorter than two days, we argue
that the shortest-period cases observed in the period-mass relation may be
explained by a model whereby planets undergo strong tidal encounters with
stars, after either being scattered by dynamical interactions into highly
eccentric orbits, or tidally captured from nearly parabolic orbits. Although
this scenario does provide a natural explanation for the edge found for planets
at twice the Roche limit, it does not explain how such planets will survive the
inevitable expansion that results from energy injection during tidal
circularization.Comment: 32 pages, 10 figures, accepted by Icarus; updated for referees
suggestions and recent observation
Filling the holes: Evolving excised binary black hole initial data with puncture techniques
We follow the inspiral and merger of equal-mass black holes (BHs) by the
moving puncture technique and demonstrate that both the exterior solution and
the asymptotic gravitational waveforms are unchanged when the initial interior
solution is replaced by constraint-violating ``junk'' initial data. We apply
this result to evolve conformal thin-sandwich (CTS) binary BH initial data by
filling their excised interiors with arbitrary, but smooth, initial data and
evolving with standard puncture gauge choices. The waveforms generated for both
puncture and filled-CTS initial data are remarkably similar, and there are only
minor differences between irrotational and corotational CTS BH binaries. Even
the interior solutions appear to evolve to the same constraint-satisfying
solution at late times, independent of the initial data.Comment: 5 pages, 5 figures, accepted by PRD Rapid Communications, RevTe
Post-Newtonian SPH Simulations of Binary Neutron Stars
Abstract. Using our Post-Newtonian SPH (smoothed particle hydrodynamics) code, we study the final coalescence and merging of neutron star (NS) binaries. We find that the gravity wave signals can be computed accurately for irrotational systems in calculations of sufficient resolution, even in the presence of Kelvin-Helmholtz instabilities
The Genomic Substrate for Adaptive Radiation: Copy Number Variation across 12 Tribes of African Cichlid Species
© 2019 Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution 2019. This work is written by US Government employees and is in the public domain in the US. The initial sequencing of five cichlid genomes revealed an accumulation of genetic variation, including extensive copy number variation in cichlid lineages particularly those that have undergone dramatic evolutionary radiation. Gene duplication has the potential to generate substantial molecular substrate for the origin of evolutionary novelty. We use array-based comparative heterologous genomic hybridization to identify copy number variation events (CNVEs) for 168 samples representing 53 cichlid species including the 5 species for which full genome sequence is available. We identify an average of 50-100 CNVEs per individual. For those species represented by multiple samples, we identify 150-200 total CNVEs suggesting a substantial amount of intraspecific variation. For these species, only ∼10% of the detected CNVEs are fixed. Hierarchical clustering of species according to CNVE data recapitulates phylogenetic relationships fairly well at both the tribe and radiation level. Although CNVEs are detected on all linkage groups, they tend to cluster in "hotspots" and are likely to contain and be flanked by transposable elements. Furthermore, we show that CNVEs impact functional categories of genes with potential roles in adaptive phenotypes that could reasonably promote divergence and speciation in the cichlid clade. These data contribute to a more complete understanding of the molecular basis for adaptive natural selection, speciation, and evolutionary radiation
Quasiequilibrium sequences of black-hole--neutron-star binaries in general relativity
We construct quasiequilibrium sequences of black hole-neutron star binaries
for arbitrary mass ratios by solving the constraint equations of general
relativity in the conformal thin-sandwich decomposition. We model the neutron
star as a stationary polytrope satisfying the relativistic equations of
hydrodynamics, and account for the black hole by imposing equilibrium boundary
conditions on the surface of an excised sphere (the apparent horizon). In this
paper we focus on irrotational configurations, meaning that both the neutron
star and the black hole are approximately nonspinning in an inertial frame. We
present results for a binary with polytropic index n=1, mass ratio
M_{irr}^{BH}/M_{B}^{NS}=5 and neutron star compaction
M_{ADM,0}^{NS}/R_0=0.0879, where M_{irr}^{BH} is the irreducible mass of the
black hole, M_{B}^{NS} the neutron star baryon rest-mass, and M_{ADM,0}^{NS}
and R_0 the neutron star Arnowitt-Deser-Misner mass and areal radius in
isolation, respectively. Our models represent valid solutions to Einstein's
constraint equations and may therefore be employed as initial data for
dynamical simulations of black hole-neutron star binaries.Comment: 5 pages, 1 figure, revtex4, published in Phys.Rev.
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