1,301 research outputs found
Estimating the detectable rate of capture of stellar mass black holes by massive central black holes in normal galaxies
The capture and subsequent inspiral of stellar mass black holes on eccentric
orbits by central massive black holes, is one of the more interesting likely
sources of gravitational radiation detectable by LISA. We estimate the rate of
observable events and the associated uncertainties. A moderately favourable
mass function could provide many detectable bursts each year, and a detection
of at least one burst per year is very likely given our current understanding
of the populations in cores of normal spiral galaxies.Comment: 3 pages 2-column revtex Latex macro. No figures. Classical and
Quantum Gravity, accepte
Angular Resolution of the LISA Gravitational Wave Detector
We calculate the angular resolution of the planned LISA detector, a
space-based laser interferometer for measuring low-frequency gravitational
waves from galactic and extragalactic sources. LISA is not a pointed
instrument; it is an all-sky monitor with a quadrupolar beam pattern. LISA will
measure simultaneously both polarization components of incoming gravitational
waves, so the data will consist of two time series. All physical properties of
the source, including its position, must be extracted from these time series.
LISA's angular resolution is therefore not a fixed quantity, but rather depends
on the type of signal and on how much other information must be extracted.
Information about the source position will be encoded in the measured signal in
three ways: 1) through the relative amplitudes and phases of the two
polarization components, 2) through the periodic Doppler shift imposed on the
signal by the detector's motion around the Sun, and 3) through the further
modulation of the signal caused by the detector's time-varying orientation. We
derive the basic formulae required to calculate the LISA's angular resolution
for a given source. We then evaluate for
two sources of particular interest: monchromatic sources and mergers of
supermassive black holes. For these two types of sources, we calculate (in the
high signal-to-noise approximation) the full variance-covariance matrix, which
gives the accuracy to which all source parameters can be measured. Since our
results on LISA's angular resolution depend mainly on gross features of the
detector geometry, orbit, and noise curve, we expect these results to be fairly
insensitive to modest changes in detector design that may occur between now and
launch. We also expect that our calculations could be easily modified to apply
to a modified design.Comment: 15 pages, 5 figures, RevTex 3.0 fil
Gravitational Helioseismology?
The magnitudes of the external gravitational perturbations associated with
the normal modes of the Sun are evaluated to determine whether these solar
oscillations could be observed with the proposed Laser Interferometer Space
Antenna (LISA), a network of satellites designed to detect gravitational
radiation. The modes of relevance to LISA---the , low-order , and
-modes---have not been conclusively observed to date. We find that the
energy in these modes must be greater than about in order
to be observable above the LISA detector noise. These mode energies are larger
than generally expected, but are much smaller than the current observational
upper limits. LISA may be confusion-limited at the relevant frequencies due to
the galactic background from short-period white dwarf binaries. Present
estimates of the number of these binaries would require the solar modes to have
energies above about to be observable by LISA.Comment: 8 pages; prepared with REVTEX 3.0 LaTeX macro
Using binary stars to bound the mass of the graviton
Interacting white dwarf binary star systems, including helium cataclysmic
variable (HeCV) systems, are expected to be strong sources of gravitational
radiation, and should be detectable by proposed space-based laser
interferometer gravitational wave observatories such as LISA. Several HeCV star
systems are presently known and can be studied optically, which will allow
electromagnetic and gravitational wave observations to be correlated.
Comparisons of the phases of a gravitational wave signal and the orbital light
curve from an interacting binary white dwarf star system can be used to bound
the mass of the graviton. Observations of typical HeCV systems by LISA could
potentially yield an upper bound on the inverse mass of the graviton as strong
as km (
eV), more than two orders of magnitude better than present solar system derived
bounds.Comment: 21 pages plus 4 figures; ReVTe
A note on light velocity anisotropy
It is proved that in experiments on or near the Earth, no anisotropy in the
one-way velocity of light may be detected. The very accurate experiments which
have been performed to detect such an effect are to be considered significant
tests of both special relativity and the equivalence principleComment: 8 pages, LaTex, Gen. Relat. Grav. accepte
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
Compact Binaries in Star Clusters I - Black Hole Binaries Inside Globular Clusters
We study the compact binary population in star clusters, focusing on binaries
containing black holes, using a self-consistent Monte Carlo treatment of
dynamics and full stellar evolution. We find that the black holes experience
strong mass segregation and become centrally concentrated. In the core the
black holes interact strongly with each other and black hole-black hole
binaries are formed very efficiently. The strong interactions, however, also
destroy or eject the black hole-black hole binaries. We find no black
hole-black hole mergers within our simulations but produce many hard escapers
that will merge in the galactic field within a Hubble time. We also find
several highly eccentric black hole-black hole binaries that are potential LISA
sources, suggesting that star clusters are interesting targets for space-based
detectors. We conclude that star clusters must be taken into account when
predicting compact binary population statistics.Comment: 19 pages, 5 Tables, 12 Figures, updated in response to referee
report, accepted for publication in MNRA
Studying the anisotropy of the gravitational wave stochastic background with LISA
A plethora of gravitational wave stochastic backgrounds populate the
sensitivity window of the Laser Interferometer Space Antenna. We show that LISA
can detect the anisotropy of the background corresponding to the multipole
moments of order l=2 and 4. The signal-to-noise ratio generated by galactic
white dwarf binary systems could be as high as 60 for 3 yrs of integration, and
LISA could provide valuable information on the spatial distribution of a
variety of galactic sources. We also show that the cross-correlation of the
data sets from two interferometers could marginally lead to meaningful
upper-limits on the degree of isotropy of the primordial gravitational wave
background.Comment: 4 pages, uses RevTe
Selection effects in resolving Galactic binaries with LISA
Using several realisations of the Galactic population of close white dwarf
binaries, we have explored the selection bias for resolved binaries in the LISA
data stream. We have assumed a data analysis routine that is capable of
identifying binaries that have a signal to noise ratio of at least 5 above a
confusion foreground of unresolved binaries. The resolved population of
binaries is separated into a subpopulation over 1000 binaries that have a
measureable chirp and another subpopulation over 20,000 binaries that do not.
As expected, the population of chirping binaries is heavily skewed toward high
frequency, high chirp mass systems, with little or no preference for nearby
systems. The population of non-chirping binaries is still biased toward
frequencies above about 1 mHz. There is an overabundance of higher mass systems
than is present in the complete Galactic population.Comment: 9 pages, 8 figures, GWDAW 11 proceeding
Gravitational waves from coalescing binaries and Doppler experiments
Doppler tracking of interplanetary spacecraft provides the only method
presently available for broad-band searches of low frequency gravitational
waves. The instruments have a peak sensitivity around the reciprocal of the
round-trip light-time T of the radio link connecting the Earth to the
space-probe and therefore are particularly suitable to search for coalescing
binaries containing massive black holes in galactic nuclei. A number of Doppler
experiments -- the most recent involving the probes ULYSSES, GALILEO and MARS
OBSERVER -- have been carried out so far; moreover, in 2002-2004 the CASSINI
spacecraft will perform three 40 days data acquisition runs with expected
sensitivity about twenty times better than that achieved so far. Central aims
of this paper are: (i) to explore, as a function of the relevant instrumental
and astrophysical parameters, the Doppler output produced by in-spiral signals
-- sinusoids of increasing frequency and amplitude (the so-called chirp); (ii)
to identify the most important parameter regions where to concentrate intense
and dedicated data analysis; (iii) to analyze the all-sky and all-frequency
sensitivity of the CASSINI's experiments, with particular emphasis on possible
astrophysical targets, such as our Galactic Centre and the Virgo Cluster.Comment: 52 pages, LaTeX, 19 Postscript Figures, submitted to Phys. Rev.
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