3,154 research outputs found

### The Final Merger of Black-Hole Binaries

Recent breakthroughs in the field of numerical relativity have led to
dramatic progress in understanding the predictions of General Relativity for
the dynamical interactions of two black holes in the regime of very strong
gravitational fields. Such black-hole binaries are important astrophysical
systems and are a key target of current and developing gravitational-wave
detectors. The waveform signature of strong gravitational radiation emitted as
the black holes fall together and merge provides a clear observable record of
the process. After decades of slow progress, these mergers and the
gravitational-wave signals they generate can now be routinely calculated using
the methods of numerical relativity. We review recent advances in understanding
the predicted physics of events and the consequent radiation, and discuss some
of the impacts this new knowledge is having in various areas of astrophysics.Comment: 57 pages; 9 figures. Updated references & fixed typos. Published
version is at
http://www.annualreviews.org/doi/abs/10.1146/annurev.nucl.010909.08324

### Black-hole binaries, gravitational waves, and numerical relativity

Understanding the predictions of general relativity for the dynamical
interactions of two black holes has been a long-standing unsolved problem in
theoretical physics. Black-hole mergers are monumental astrophysical events,
releasing tremendous amounts of energy in the form of gravitational radiation,
and are key sources for both ground- and space-based gravitational-wave
detectors. The black-hole merger dynamics and the resulting gravitational
waveforms can only be calculated through numerical simulations of Einstein's
equations of general relativity. For many years, numerical relativists
attempting to model these mergers encountered a host of problems, causing their
codes to crash after just a fraction of a binary orbit could be simulated.
Recently, however, a series of dramatic advances in numerical relativity has
allowed stable, robust black-hole merger simulations. This remarkable progress
in the rapidly maturing field of numerical relativity, and the new
understanding of black-hole binary dynamics that is emerging is chronicled.
Important applications of these fundamental physics results to astrophysics, to
gravitational-wave astronomy, and in other areas are also discussed.Comment: 54 pages, 42 figures. Some typos corrected & references updated.
Essentially final published versio

### Decoding mode-mixing in black-hole merger ringdown

Optimal extraction of information from gravitational-wave observations of
binary black-hole coalescences requires detailed knowledge of the waveforms.
Current approaches for representing waveform information are based on
spin-weighted spherical harmonic decomposition. Higher-order harmonic modes
carrying a few percent of the total power output near merger can supply
information critical to determining intrinsic and extrinsic parameters of the
binary. One obstacle to constructing a full multi-mode template of merger
waveforms is the apparently complicated behavior of some of these modes;
instead of settling down to a simple quasinormal frequency with decaying
amplitude, some $|m| \neq \ell$ modes show periodic bumps characteristic of
mode-mixing. We analyze the strongest of these modes -- the anomalous $(3,2)$
harmonic mode -- measured in a set of binary black-hole merger waveform
simulations, and show that to leading order, they are due to a mismatch between
the spherical harmonic basis used for extraction in 3D numerical relativity
simulations, and the spheroidal harmonics adapted to the perturbation theory of
Kerr black holes. Other causes of mode-mixing arising from gauge ambiguities
and physical properties of the quasinormal ringdown modes are also considered
and found to be small for the waveforms studied here.Comment: 15 pages, 10 figures, 2 tables; new version has improved Figs. 1-3,
consistent labelling of simulations between Tables I & II,
additional/corrected references, and extra hyphen

### Post-Newtonian Initial Data with Waves: Progress in Evolution

In Kelly et al. [Phys. Rev. D, 76:024008, 2007], we presented new binary
black-hole initial data adapted to puncture evolutions in numerical relativity.
This data satisfies the constraint equations to 2.5 post-Newtonian order, and
contains a transverse-traceless "wavy" metric contribution, violating the
standard assumption of conformal flatness. We report on progress in evolving
this data with a modern moving-puncture implementation of the BSSN equations in
several numerical codes. We discuss the effect of the new metric terms on junk
radiation and continuity of physical radiation extracted.Comment: 13 pages, 9 figures. Invited paper from Numerical Relativity and Data
Analysis (NRDA) 2009, Albert Einstein Institute, Potsdam. Corrected to match
published version

### Gravitational-Wave Data Analysis with Spinning Merger-Ringdown Waveforms

The recent availability of high-quality, gravitational merger-ringdown waveforms from spinning black-hole systems has made possible the development of multi-mode GW templates for use in data-analysis studies of current and proposed interferometric GW detectors. We report on recent work at NASA Goddard, analyzing the most significant modes from aligned-spin black-hole-binary mergers. From these, we have developed time-domain merger-ringdown GW templates covering the aligned-spin portion of parameter space. We also discuss how using the full information content of aligned-spin mergers can significantly reduce uncertainties in some parameters, emphasizing the significant gains possible in the last stages of merger, inaccessible to inspiral-only post-Newtonian templates

### Observing mergers of non-spinning black-hole binaries

Advances in the field of numerical relativity now make it possible to
calculate the final, most powerful merger phase of binary black-hole
coalescence for generic binaries. The state of the art has advanced well beyond
the equal-mass case into the unequal-mass and spinning regions of parameter
space. We present a study of the nonspinning portion of parameter space,
primarily using an analytic waveform model tuned to available numerical data,
with an emphasis on observational implications. We investigate the impact of
varied mass ratio on merger signal-to-noise ratios (SNRs) for several
detectors, and compare our results with expectations from the test-mass limit.
We note a striking similarity of the waveform phasing of the merger waveform
across the available mass ratios. Motivated by this, we calculate the match
between our 1:1 (equal mass) and 4:1 mass-ratio waveforms during the merger as
a function of location on the source sky, using a new formalism for the match
that accounts for higher harmonics. This is an indicator of the amount of
degeneracy in mass ratio for mergers of moderate-mass-ratio systems.Comment: 13 pages, 11 figures, submitted to Phys. Rev.

### Electromagnetic Chirps from Neutron Star-Black Hole Mergers

We calculate the electromagnetic signal of a gamma-ray flare coming from the
surface of a neutron star shortly before merger with a black hole companion.
Using a new version of the Monte Carlo radiation transport code Pandurata that
incorporates dynamic spacetimes, we integrate photon geodesics from the neutron
star surface until they reach a distant observer or are captured by the black
hole. The gamma-ray light curve is modulated by a number of relativistic
effects, including Doppler beaming and gravitational lensing. Because the
photons originate from the inspiraling neutron star, the light curve closely
resembles the corresponding gravitational waveform: a chirp signal
characterized by a steadily increasing frequency and amplitude. We propose to
search for these electromagnetic chirps using matched filtering algorithms
similar to those used in LIGO data analysis.Comment: 13 pages, 5 figures, submitted to Ap

### Prompt Electromagnetic Transients from Binary Black Hole Mergers

Binary black hole (BBH) mergers provide a prime source for current and future
interferometric GW observatories. Massive BBH mergers may often take place in
plasma-rich environments, leading to the exciting possibility of a concurrent
electromagnetic (EM) signal observable by traditional astronomical facilities.
However, many critical questions about the generation of such counterparts
remain unanswered. We explore mechanisms that may drive EM counterparts with
magnetohydrodynamic simulations treating a range of scenarios involving
equal-mass black-hole binaries immersed in an initially homogeneous fluid with
uniform, orbitally aligned magnetic fields. We find that the time development
of Poynting luminosity, which may drive jet-like emissions, is relatively
insensitive to aspects of the initial configuration. In particular, over a
significant range of initial values, the central magnetic field strength is
effectively regulated by the gas flow to yield a Poynting luminosity of
$10^{45}-10^{46} \rho_{-13} M_8^2 \, {\rm erg}\,{\rm s}^{-1}$, with BBH mass
scaled to $M_8 \equiv M/(10^8 M_{\odot})$ and ambient density $\rho_{-13}
\equiv \rho/(10^{-13} \, {\rm g} \, {\rm cm}^{-3})$. We also calculate the
direct plasma synchrotron emissions processed through geodesic ray-tracing.
Despite lensing effects and dynamics, we find the observed synchrotron flux
varies little leading up to merger.Comment: 22 pages, 21 figures; additional reference + clarifying text added to
match published versio

### Improved Moving Puncture Gauge Conditions for Compact Binary Evolutions

Robust gauge conditions are critically important to the stability and
accuracy of numerical relativity (NR) simulations involving compact objects.
Most of the NR community use the highly robust---though
decade-old---moving-puncture (MP) gauge conditions for such simulations. It has
been argued that in binary black hole (BBH) evolutions adopting this gauge,
noise generated near adaptive-mesh-refinement (AMR) boundaries does not
converge away cleanly with increasing resolution, severely limiting
gravitational waveform accuracy at computationally feasible resolutions. We
link this noise to a sharp (short-wavelength), initial outgoing gauge wave
crossing into progressively lower resolution AMR grids, and present
improvements to the standard MP gauge conditions that focus on stretching,
smoothing, and more rapidly settling this outgoing wave. Our best gauge choice
greatly reduces gravitational waveform noise during inspiral, yielding less
fluctuation in convergence order and $\sim 40%$ lower waveform phase and
amplitude errors at typical resolutions. Noise in other physical quantities of
interest is also reduced, and constraint violations drop by more than an order
of magnitude. We expect these improvements will carry over to simulations of
all types of compact binary systems, as well as other $N$+1 formulations of
gravity for which MP-like gauge conditions can be chosen.Comment: 25 pages, 16 figures, 2 tables. Matches published versio

### Consistency of post-Newtonian waveforms with numerical relativity

General relativity predicts the gravitational wave signatures of coalescing
binary black holes. Explicit waveform predictions for such systems, required
for optimal analysis of observational data, have so far been achieved using the
post-Newtonian (PN) approximation. The quality of this treatment is unclear,
however, for the important late-inspiral portion. We derive late-inspiral
waveforms via a complementary approach, direct numerical simulation of
Einstein's equations. We compare waveform phasing from simulations of the last
$\sim 14$ cycles of gravitational radiation from equal-mass, nonspinning black
holes with the corresponding 2.5PN, 3PN, and 3.5PN orbital phasing. We find
phasing agreement consistent with internal error estimates based on either
approach, suggesting that PN waveforms for this system are effective until the
last orbit prior to final merger.Comment: Replaced with published version -- one figure removed, text and other
figures updated for clarity of discussio

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