2,679 research outputs found
Evolution of circular, non-equatorial orbits of Kerr black holes due to gravitational-wave emission: II. Inspiral trajectories and gravitational waveforms
The inspiral of a ``small'' () compact body into a
``large'' () black hole is a key source of
gravitational radiation for the space-based gravitational-wave observatory
LISA. The waves from such inspirals will probe the extreme strong-field nature
of the Kerr metric. In this paper, I investigate the properties of a restricted
family of such inspirals (the inspiral of circular, inclined orbits) with an
eye toward understanding observable properties of the gravitational waves that
they generate. Using results previously presented to calculate the effects of
radiation reaction, I assemble the inspiral trajectories (assuming that
radiation reacts adiabatically, so that over short timescales the trajectory is
approximately geodesic) and calculate the wave generated as the compact body
spirals in. I do this analysis for several black hole spins, sampling a range
that should be indicative of what spins we will encounter in nature. The spin
has a very strong impact on the waveform. In particular, when the hole rotates
very rapidly, tidal coupling between the inspiraling body and the event horizon
has a very strong influence on the inspiral time scale, which in turn has a big
impact on the gravitational wave phasing. The gravitational waves themselves
are very usefully described as ``multi-voice chirps'': the wave is a sum of
``voices'', each corresponding to a different harmonic of the fundamental
orbital frequencies. Each voice has a rather simple phase evolution. Searching
for extreme mass ratio inspirals voice-by-voice may be more effective than
searching for the summed waveform all at once.Comment: 15 pages, 11 figures, accepted for publication in PRD. This version
incorporates referee's comments, and is much less verbos
Self force on particle in orbit around a black hole
We study the self force acting on a scalar charge in uniform circular motion
around a Schwarzschild black hole. The analysis is based on a direct
calculation of the self force via mode decomposition, and on a regularization
procedure based on Ori's mode-sum regularization prescription. We find the four
self-force at arbitrary radii and angular velocities (both geodesic and
non-geodesic), in particular near the black hole, where general-relativistic
effects are strongest, and for fast motion. We find the radial component of the
self force to be repulsive or attractive, depending on the orbit.Comment: RevTeX, 4 pages, 4 Encapsulated PostScript figures. Submitted to
Phys. Rev. Let
Measuring gravitational waves from binary black hole coalescences: II. the waves' information and its extraction, with and without templates
We discuss the extraction of information from detected binary black hole
(BBH) coalescence gravitational waves, focusing on the merger phase that occurs
after the gradual inspiral and before the ringdown. Our results are: (1) If
numerical relativity simulations have not produced template merger waveforms
before BBH detections by LIGO/VIRGO, one can band-pass filter the merger waves.
For BBHs smaller than about 40 solar masses detected via their inspiral waves,
the band pass filtering signal to noise ratio indicates that the merger waves
should typically be just barely visible in the noise for initial and advanced
LIGO interferometers. (2) We derive an optimized (maximum likelihood) method
for extracting a best-fit merger waveform from the noisy detector output; one
"perpendicularly projects" this output onto a function space (specified using
wavelets) that incorporates our prior knowledge of the waveforms. An extension
of the method allows one to extract the BBH's two independent waveforms from
outputs of several interferometers. (3) If numerical relativists produce codes
for generating merger templates but running the codes is too expensive to allow
an extensive survey of the merger parameter space, then a coarse survey of this
parameter space, to determine the ranges of the several key parameters and to
explore several qualitative issues which we describe, would be useful for data
analysis purposes. (4) A complete set of templates could be used to test the
nonlinear dynamics of general relativity and to measure some of the binary
parameters. We estimate the number of bits of information obtainable from the
merger waves (about 10 to 60 for LIGO/VIRGO, up to 200 for LISA), estimate the
information loss due to template numerical errors or sparseness in the template
grid, and infer approximate requirements on template accuracy and spacing.Comment: 33 pages, Rextex 3.1 macros, no figures, submitted to Phys Rev
Extreme Mass Ratio Inspirals: LISA's unique probe of black hole gravity
In this review article I attempt to summarise past and present-ongoing-work
on the problem of the inspiral of a small body in the gravitational field of a
much more massive Kerr black hole. Such extreme mass ratio systems, expected to
occur in galactic nuclei, will constitute prime sources of gravitational
radiation for the future LISA gravitational radiation detector. The article's
main goal is to provide a survey of basic celestial mechanics in Kerr spacetime
and calculations of gravitational waveforms and backreaction on the small
body's orbital motion, based on the traditional `flux-balance' method and the
Teukolsky black hole perturbation formalism.Comment: Invited review article, 45 pages, 23 figure
Gravitational Waves from a Compact Star in a Circular, Inspiral Orbit, in the Equatorial Plane of a Massive, Spinning Black Hole, as Observed by LISA
Results are presented from high-precision computations of the orbital
evolution and emitted gravitational waves for a stellar-mass object spiraling
into a massive black hole in a slowly shrinking, circular, equatorial orbit.
The focus of these computations is inspiral near the innermost stable circular
orbit (isco)---more particularly, on orbits for which the angular velocity
Omega is 0.03 < Omega/Omega_{isco} < 1. The computations are based on the
Teukolsky-Sasaki-Nakamura formalism, and the results are tabulated in a set of
functions that are of order unity and represent relativistic corrections to
low-orbital-velocity formulas. These tables can form a foundation for future
design studies for the LISA space-based gravitational-wave mission. A first
survey of applications to LISA is presented: Signal to noise ratios S/N are
computed and graphed as functions of the time-evolving gravitational-wave
frequency for representative values of the hole's mass M and spin a and the
inspiraling object's mass \mu, with the distance to Earth chosen to be r_o = 1
Gpc. These S/N's show a very strong dependence on the black-hole spin, as well
as on M and \mu. A comparison with predicted event rates shows strong promise
for detecting these waves, but not beyond about 1Gpc if the inspiraling object
is a white dwarf or neutron star. This argues for a modest lowering of LISA's
noise floor. A brief discussion is given of the prospects for extracting
information from the observed wavesComment: Physical Review D, in press; 21 pages, 9 figures, 10 tables it is
present in the RevTeX fil
Cosmology with coalescing massive black holes
The gravitational waves generated in the coalescence of massive binary black
holes will be measurable by LISA to enormous distances. Redshifts z~10 or
larger (depending somewhat on the mass of the binary) can potentially be probed
by such measurements, suggesting that binary coalescences can be made into
cosmological tools. We discuss two particularly interesting types of probes.
First, by combining gravitational-wave measurements with information about the
universe's cosmography, we can study the evolution of black hole masses and
merger rates as a function of redshift, providing information about the growth
of structures at high redshift and possibly constraining hierarchical merger
scenarios. Second, if it is possible to associate an ``electromagnetic''
counterpart with a coalescence, it may be possible to measure both redshift and
luminosity distance to an event with less than ~1% error. Such a measurement
would constitute an amazingly precise cosmological standard candle.
Unfortunately, gravitational lensing uncertainties will reduce the quality of
this candle significantly. Though not as amazing as might have been hoped, such
a candle would nonetheless very usefully complement other distance-redshift
probes, in particular providing a valuable check on systematic effects in such
measurements.Comment: 8 pages, 4 figure
Discounting collateral:Quants, derivatives, and the reconstruction of the ârisk-free rateâ after the financial crisis
Gravitational waves from cosmological compact binaries
We consider gravitational waves emitted by various populations of compact
binaries at cosmological distances. We use population synthesis models to
characterize the properties of double neutron stars, double black holes and
double white dwarf binaries as well as white dwarf-neutron star, white
dwarf-black hole and black hole-neutron star systems. We use the
observationally determined cosmic star formation history to reconstruct the
redshift distribution of these sources and their merging rate evolution. The
gravitational signals emitted by each source during its early-inspiral phase
add randomly to produce a stochastic background in the low frequency band with
spectral strain amplitude between 10^{-18} Hz^{-1/2} and
5 10^{-17} Hz^{-1/2} at frequencies in the interval [5 10^{-6}-5 10^{-5}] Hz.
The overall signal which, at frequencies above 10^{-4}Hz, is largely dominated
by double white dwarf systems, might be detectable with LISA in the frequency
range [1-10] mHz and acts like a confusion limited noise component which might
limit the LISA sensitivity at frequencies above 1 mHz.Comment: 14 pages, 14 figures, uses mn.sty, submitted to MNRA
Measuring gravitational waves from binary black hole coalescences: I. Signal to noise for inspiral, merger, and ringdown
We estimate the expected signal-to-noise ratios (SNRs) from the three phases
(inspiral,merger,ringdown) of coalescing binary black holes (BBHs) for initial
and advanced ground-based interferometers (LIGO/VIRGO) and for space-based
interferometers (LISA). LIGO/VIRGO can do moderate SNR (a few tens), moderate
accuracy studies of BBH coalescences in the mass range of a few to about 2000
solar masses; LISA can do high SNR (of order 10^4) high accuracy studies in the
mass range of about 10^5 to 10^8 solar masses. BBHs might well be the first
sources detected by LIGO/VIRGO: they are visible to much larger distances (up
to 500 Mpc by initial interferometers) than coalescing neutron star binaries
(heretofore regarded as the "bread and butter" workhorse source for LIGO/VIRGO,
visible to about 30 Mpc by initial interferometers). Low-mass BBHs (up to 50
solar masses for initial LIGO interferometers; 100 for advanced; 10^6 for LISA)
are best searched for via their well-understood inspiral waves; higher mass
BBHs must be searched for via their poorly understood merger waves and/or their
well-understood ringdown waves. A matched filtering search for massive BBHs
based on ringdown waves should be capable of finding BBHs in the mass range of
about 100 to 700 solar masses out to 200 Mpc (initial LIGO interferometers),
and 200 to 3000 solar masses out to about z=1 (advanced interferometers). The
required number of templates is of order 6000 or less. Searches based on merger
waves could increase the number of detected massive BBHs by a factor of order
10 or more over those found from inspiral and ringdown waves, without detailed
knowledge of the waveform shapes, using a "noise monitoring" search algorithm.
A full set of merger templates from numerical relativity could further increase
the number of detected BBHs by an additional factor of up to 4.Comment: 40 pages, Revtex, psfig.tex, seven figures, submitted to Phys Rev
Mutations of the BRAF gene in human cancer
Cancers arise owing to the accumulation of mutations in critical genes that alter normal programmes of cell proliferation, differentiation and death. As the first stage of a systematic genome-wide screen for these genes, we have prioritized for analysis signalling pathways in which at least one gene is mutated in human cancer. The RAS RAF MEK ERK MAP kinase pathway mediates cellular responses to growth signals. RAS is mutated to an oncogenic form in about 15% of human cancer. The three RAF genes code for cytoplasmic serine/threonine kinases that are regulated by binding RAS. Here we report BRAF somatic missense mutations in 66% of malignant melanomas and at lower frequency in a wide range of human cancers. All mutations are within the kinase domain, with a single substitution (V599E) accounting for 80%. Mutated BRAF proteins have elevated kinase activity and are transforming in NIH3T3 cells. Furthermore, RAS function is not required for the growth of cancer cell lines with the V599E mutation. As BRAF is a serine/threonine kinase that is commonly activated by somatic point mutation in human cancer, it may provide new therapeutic opportunities in malignant melanoma
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