1,154 research outputs found
Black hole-neutron star mergers for 10 solar mass black holes
General relativistic simulations of black hole-neutron star mergers have
currently been limited to low-mass black holes (less than 7 solar mass), even
though population synthesis models indicate that a majority of mergers might
involve more massive black holes (10 solar mass or more). We present the first
general relativistic simulations of black hole-neutron star mergers with 10
solar mass black holes. For massive black holes, the tidal forces acting on the
neutron star are usually too weak to disrupt the star before it reaches the
innermost stable circular orbit of the black hole. Varying the spin of the
black hole in the range a/M = 0.5-0.9, we find that mergers result in the
disruption of the star and the formation of a massive accretion disk only for
large spins a/M>0.7-0.9. From these results, we obtain updated constraints on
the ability of BHNS mergers to be the progenitors of short gamma-ray bursts as
a function of the mass and spin of the black hole. We also discuss the
dependence of the gravitational wave signal on the black hole parameters, and
provide waveforms and spectra from simulations beginning 7-8 orbits before
merger.Comment: 11 pages, 11 figures - Updated to match published versio
A Structured Framework and Resources to Use to Get Your Medical Education Work Published.
IntroductionMedical educators often have great ideas for medical education scholarship but have difficulty converting their educational abstract or project into a published manuscript.MethodsDuring this workshop, participants addressed common challenges in developing an educational manuscript. In small-group case scenarios, participants discovered the importance of the "So what?" in making the case for their project. Incorporating conceptual frameworks, participants chose appropriate outcome metrics, discussed how to frame the discussion section, and ensured appropriate journal fit. After each small-group exercise, large-group discussions allowed the small groups to report back so that facilitators could highlight and reinforce key learning points. At the conclusion of the workshop, participants left with a checklist for creating an educational manuscript and an additional resources document to assist them in avoiding common pitfalls when turning their educational abstract/project into a publishable manuscript.ResultsThis workshop was presented in 2016 and 2017. Presenter evaluations were completed by 33 participants; 11 completed conference evaluations. The mean overall rating on presenter evaluations was 4.55 out of 5, while the conference evaluations mean was 3.73 out of 4. Comments provided on both evaluation tools highlighted the perceived effectiveness of the delivery and content. More than 50% of respondents stated that they planned to incorporate the use of conceptual frameworks in future work.DiscussionThis workshop helped participants address common challenges by providing opportunities for hands-on practice as well as tips and resources for use when submitting a medical education manuscript for publication
Comparing Gravitational Waveform Extrapolation to Cauchy-Characteristic Extraction in Binary Black Hole Simulations
We extract gravitational waveforms from numerical simulations of black hole
binaries computed using the Spectral Einstein Code. We compare two extraction
methods: direct construction of the Newman-Penrose (NP) scalar at a
finite distance from the source and Cauchy-characteristic extraction (CCE). The
direct NP approach is simpler than CCE, but NP waveforms can be contaminated by
near-zone effects---unless the waves are extracted at several distances from
the source and extrapolated to infinity. Even then, the resulting waveforms can
in principle be contaminated by gauge effects. In contrast, CCE directly
provides, by construction, gauge-invariant waveforms at future null infinity.
We verify the gauge invariance of CCE by running the same physical simulation
using two different gauge conditions. We find that these two gauge conditions
produce the same CCE waveforms but show differences in extrapolated-
waveforms. We examine data from several different binary configurations and
measure the dominant sources of error in the extrapolated- and CCE
waveforms. In some cases, we find that NP waveforms extrapolated to infinity
agree with the corresponding CCE waveforms to within the estimated error bars.
However, we find that in other cases extrapolated and CCE waveforms disagree,
most notably for "memory" modes.Comment: 26 pages, 20 figure
Initial data for black hole-neutron star binaries, with rotating stars
The coalescence of a neutron star with a black hole is a primary science
target of ground-based gravitational wave detectors. Constraining or measuring
the neutron star spin directly from gravitational wave observations requires
knowledge of the dependence of the emission properties of these systems on the
neutron star spin. This paper lays foundations for this task, by developing a
numerical method to construct initial data for black hole--neutron star
binaries with arbitrary spin on the neutron star. We demonstrate the robustness
of the code by constructing initial-data sets in large regions of the parameter
space. In addition to varying the neutron star spin-magnitude and
spin-direction, we also explore neutron star compactness, mass-ratio, black
hole spin, and black hole spin-direction. Specifically, we are able to
construct initial data sets with neutron stars spinning near centrifugal
break-up, and with black hole spins as large as .Comment: 25 pages, 12 figure
Fast and accurate prediction of numerical relativity waveforms from binary black hole coalescences using surrogate models
Simulating a binary black hole (BBH) coalescence by solving Einstein's
equations is computationally expensive, requiring days to months of
supercomputing time. Using reduced order modeling techniques, we construct an
accurate surrogate model, which is evaluated in a millisecond to a second, for
numerical relativity (NR) waveforms from non-spinning BBH coalescences with
mass ratios in and durations corresponding to about orbits
before merger. We assess the model's uncertainty and show that our modeling
strategy predicts NR waveforms {\em not} used for the surrogate's training with
errors nearly as small as the numerical error of the NR code. Our model
includes all spherical-harmonic waveform modes resolved by
the NR code up to We compare our surrogate model to Effective One
Body waveforms from - for advanced LIGO detectors and find
that the surrogate is always more faithful (by at least an order of magnitude
in most cases).Comment: Updated to published version, which includes a section comparing the
surrogate and effective-one-body models. The surrogate is publicly available
for download at http://www.black-holes.org/surrogates/ . 6 pages, 6 figure
Massive disk formation in the tidal disruption of a neutron star by a nearly extremal black hole
Black hole-neutron star (BHNS) binaries are important sources of
gravitational waves for second-generation interferometers, and BHNS mergers are
also a proposed engine for short, hard gamma-ray bursts. The behavior of both
the spacetime (and thus the emitted gravitational waves) and the neutron star
matter in a BHNS merger depend strongly and nonlinearly on the black hole's
spin. While there is a significant possibility that astrophysical black holes
could have spins that are nearly extremal (i.e. near the theoretical maximum),
to date fully relativistic simulations of BHNS binaries have included
black-hole spins only up to =0.9, which corresponds to the black hole
having approximately half as much rotational energy as possible, given the
black hole's mass. In this paper, we present a new simulation of a BHNS binary
with a mass ratio and black-hole spin =0.97, the highest simulated
to date. We find that the black hole's large spin leads to the most massive
accretion disk and the largest tidal tail outflow of any fully relativistic
BHNS simulations to date, even exceeding the results implied by extrapolating
results from simulations with lower black-hole spin. The disk appears to be
remarkably stable. We also find that the high black-hole spin persists until
shortly before the time of merger; afterwards, both merger and accretion spin
down the black hole.Comment: 20 pages, 10 figures, submitted to Classical and Quantum Gravit
Improved methods for simulating nearly extremal binary black holes
Astrophysical black holes could be nearly extremal (that is, rotating nearly
as fast as possible); therefore, nearly extremal black holes could be among the
binaries that current and future gravitational-wave observatories will detect.
Predicting the gravitational waves emitted by merging black holes requires
numerical-relativity simulations, but these simulations are especially
challenging when one or both holes have mass and spin exceeding the
Bowen-York limit of . We present improved methods that enable us to
simulate merging, nearly extremal black holes more robustly and more
efficiently. We use these methods to simulate an unequal-mass, precessing
binary black hole coalescence, where the larger black hole has . We
also use these methods to simulate a non-precessing binary black hole
coalescence, where both black holes have , nearly reaching the
Novikov-Thorne upper bound for holes spun up by thin accretion disks. We
demonstrate numerical convergence and estimate the numerical errors of the
waveforms; we compare numerical waveforms from our simulations with
post-Newtonian and effective-one-body waveforms; we compare the evolution of
the black-hole masses and spins with analytic predictions; and we explore the
effect of increasing spin magnitude on the orbital dynamics (the so-called
"orbital hangup" effect).Comment: 18 pages, 18 figure
Inspiral-merger-ringdown waveforms of spinning, precessing black-hole binaries in the effective-one-body formalism
We describe a general procedure to generate spinning, precessing waveforms
that include inspiral, merger and ringdown stages in the effective-one-body
(EOB) approach. The procedure uses a precessing frame in which
precession-induced amplitude and phase modulations are minimized, and an
inertial frame, aligned with the spin of the final black hole, in which we
carry out the matching of the inspiral-plunge to merger-ringdown waveforms. As
a first application, we build spinning, precessing EOB waveforms for the
gravitational modes l=2 such that in the nonprecessing limit those waveforms
agree with the EOB waveforms recently calibrated to numerical-relativity
waveforms. Without recalibrating the EOB model, we then compare EOB and
post-Newtonian precessing waveforms to two numerical-relativity waveforms
produced by the Caltech-Cornell-CITA collaboration. The numerical waveforms are
strongly precessing and have 35 and 65 gravitational-wave cycles. We find a
remarkable agreement between EOB and numerical-relativity precessing waveforms
and spins' evolutions. The phase difference is ~ 0.2 rad at merger, while the
mismatches, computed using the advanced-LIGO noise spectral density, are below
2% when maximizing only on the time and phase at coalescence and on the
polarization angle.Comment: 17 pages, 10 figure
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