98 research outputs found
Measuring black-hole parameters and testing general relativity using gravitational-wave data from space-based interferometers
Among the expected sources of gravitational waves for the Laser
Interferometer Space Antenna (LISA) is the capture of solar-mass compact stars
by massive black holes residing in galactic centers. We construct a simple
model for such a capture, in which the compact star moves freely on a circular
orbit in the equatorial plane of the massive black hole. We consider the
gravitational waves emitted during the late stages of orbital evolution,
shortly before the orbiting mass reaches the innermost stable circular orbit.
We construct a simple model for the gravitational-wave signal, in which the
phasing of the waves plays the dominant role. The signal's behavior depends on
a number of parameters, including , the mass of the orbiting star, ,
the mass of the central black hole, and , the black hole's angular momentum.
We calculate, using our simplified model, and in the limit of large
signal-to-noise ratio, the accuracy with which these quantities can be
estimated during a gravitational-wave measurement. Our simplified model also
suggests a method for experimentally testing the strong-field predictions of
general relativity.Comment: ReVTeX, 16 pages, 5 postscript figure
Gravitational waves from inspiralling compact binaries: Parameter estimation using second-post-Newtonian waveforms
The parameters of inspiralling compact binaries can be estimated using
matched filtering of gravitational-waveform templates against the output of
laser-interferometric gravitational-wave detectors. Using a recently calculated
formula, accurate to second post-Newtonian (2PN) order [order , where
is the orbital velocity], for the frequency sweep () induced by
gravitational radiation damping, we study the statistical errors in the
determination of such source parameters as the ``chirp mass'' , reduced
mass , and spin parameters and (related to spin-orbit and
spin-spin effects, respectively). We find that previous results using template
phasing accurate to 1.5PN order actually underestimated the errors in ,
, and . For two inspiralling neutron stars, the measurement errors
increase by less than 16 percent.Comment: 14 pages, ReVTe
Gravitational radiation from a particle in circular orbit around a black hole. VI. Accuracy of the post-Newtonian expansion
A particle of mass moves on a circular orbit around a nonrotating black
hole of mass . Under the assumption the gravitational waves
emitted by such a binary system can be calculated exactly numerically using
black-hole perturbation theory. If, further, the particle is slowly moving,
then the waves can be calculated approximately analytically, and expressed in
the form of a post-Newtonian expansion. We determine the accuracy of this
expansion in a quantitative way by calculating the reduction in signal-to-noise
ratio incurred when matched filtering the exact signal with a nonoptimal,
post-Newtonian filter.Comment: 5 pages, ReVTeX, 1 figure. A typographical error was discovered in
the computer code used to generate the results presented in the paper. The
corrected results are presented in an Erratum, which also incorporates new
results, obtained using the recently improved post-Newtonian calculations of
Tanaka, Tagoshi, and Sasak
Gravitational waves from coalescing binaries: detection strategies and Monte Carlo estimation of parameters
The paper deals with issues pertaining the detection of gravitational waves
from coalescing binaries. We introduce the application of differential geometry
to the problem of optimal detection of the `chirp signal'. We have also carried
out extensive Monte Carlo simulations to understand the errors in the
estimation of parameters of the binary system. We find that the errors are much
more than those predicted by the covariance matrix even at a high SNR of 10-15.
We also introduce the idea of using the instant of coalescence rather than the
time of arrival to determine the direction to the source.Comment: 28 pages, REVTEX, 12 figures (bundled via uufiles command along with
this paper) submitted to Phys. Rev.
Towards the statistical detection of the warm-hot intergalactic medium in intercluster filaments of the cosmic web.
Modern analyses of structure formation predict a universe tangled in a ‘cosmic web’ of dark matter and diffuse baryons. These theories further predict that at low z, a significant fraction of the baryons will be shock-heated to T ∼ 105–107 K yielding a warm–hot intergalactic medium (WHIM), but whose actual existence has eluded a firm observational confirmation. We present a novel experiment to detect the WHIM, by targeting the putative filaments connecting galaxy clusters. We use HST/COS to observe a remarkable quasi-stellar object (QSO) sightline that passes within Δd = 3 Mpc from the seven intercluster axes connecting seven independent cluster pairs at redshifts 0.1 ≤ z ≤ 0.5. We find tentative excesses of total H I, narrow H I (NLA; Doppler parameters b < 50 km s−1), broad H I (BLA; b ≥ 50 km s−1) and O VI absorption lines within rest-frame velocities of Δv ≲ 1000 km s−1 from the cluster-pairs redshifts, corresponding to ∼2, ∼1.7, ∼6 and ∼4 times their field expectations, respectively. Although the excess of O VI likely comes from gas close to individual galaxies, we conclude that most of the excesses of NLAs and BLAs are truly intergalactic. We find the covering fractions, fc, of BLAs close to cluster pairs are ∼4–7 times higher than the random expectation (at the ∼2σ c.l.), whereas the fc of NLAs and O VI are not significantly enhanced. We argue that a larger relative excess of BLAs compared to those of NLAs close to cluster pairs may be a signature of the WHIM in intercluster filaments. By extending this analysis to tens of sightlines, our experiment offers a promising route to detect the WHIM
Gravitational Wave Chirp Search: Economization of PN Matched Filter Bank via Cardinal Interpolation
The final inspiral phase in the evolution of a compact binary consisting of
black holes and/or neutron stars is among the most probable events that a
network of ground-based interferometric gravitational wave detectors is likely
to observe. Gravitational radiation emitted during this phase will have to be
dug out of noise by matched-filtering (correlating) the detector output with a
bank of several templates, making the computational resources required
quite demanding, though not formidable. We propose an interpolation method for
evaluating the correlation between template waveforms and the detector output
and show that the method is effective in substantially reducing the number of
templates required. Indeed, the number of templates needed could be a factor
smaller than required by the usual approach, when the minimal overlap
between the template bank and an arbitrary signal (the so-called {\it minimal
match}) is 0.97. The method is amenable to easy implementation, and the various
detector projects might benefit by adopting it to reduce the computational
costs of inspiraling neutron star and black hole binary search.Comment: scheduled for publicatin on Phys. Rev. D 6
On the connection between the intergalactic medium and galaxies: the H I–galaxy cross-correlation at z ≲ 1
We present a new optical spectroscopic survey of 1777 ‘star-forming’ (‘SF’) and 366 ‘non-star-forming’ (‘non-SF’) galaxies at redshifts z ∼ 0-1 (2143 in total), 22 AGN and 423 stars, observed by instruments such as the Deep Imaging Multi-Object Spectrograph, the Visible Multi-Object Spectrograph and the Gemini Multi-Object Spectrograph, in three fields containing five quasi-stellar objects (QSOs) with Hubble Space Telescope (HST) ultraviolet spectroscopy. We also present a new spectroscopic survey of 173 ‘strong’ (1014 ≤ NHI≲ 1017 cm−2) and 496 ‘weak’ (1013 ≲ NHI 50 per cent of ‘weak’ H i systems reside within galaxy voids (hence not correlated with galaxies), and are confined in dark matter haloes of masses smaller than those hosting ‘strong’ systems and/or galaxies. We speculate that H i systems within galaxy voids might still be evolving in the linear regime even at scales ≲2 Mpc
Holographic Gravitational Anomalies
In the AdS/CFT correspondence one encounters theories that are not invariant
under diffeomorphisms. In the boundary theory this is a gravitational anomaly,
and can arise in 4k+2 dimensions. In the bulk, there can be gravitational
Chern-Simons terms which vary by a total derivative. We work out the
holographic stress tensor for such theories, and demonstrate agreement between
the bulk and boundary. Anomalies lead to novel effects, such as a nonzero
angular momentum for global AdS(3). In string theory such Chern-Simons terms
are known with exact coefficients. The resulting anomalies, combined with
symmetries, imply corrections to the Bekenstein-Hawking entropy of black holes
that agree exactly with the microscopic counting.Comment: 25 page
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
Gravitational radiation from a particle in circular orbit around a black hole. V. Black-hole absorption and tail corrections
A particle of mass moves on a circular orbit of a nonrotating black
hole of mass . Under the restrictions and , where
is the orbital velocity, we consider the gravitational waves emitted by such a
binary system. We calculate , the rate at which the gravitational
waves remove energy from the system. The total energy loss is given by , where denotes that part of the
gravitational-wave energy which is carried off to infinity, while
denotes the part which is absorbed by the black hole. We show that the
black-hole absorption is a small effect: . We
also compare the wave generation formalism which derives from perturbation
theory to the post-Newtonian formalism of Blanchet and Damour. Among other
things we consider the corrections to the asymptotic gravitational-wave field
which are due to wave-propagation (tail) effects.Comment: ReVTeX, 17 page
- …