175 research outputs found
Compact Binaries in Star Clusters II - Escapers and Detection Rates
We use a self-consistent Monte Carlo treatment of stellar dynamics to
investigate black hole binaries that are dynamically ejected from globular
clusters to determine if they will be gravitational wave sources. We find that
many of the ejected binaries have initially short periods and will merge within
a Hubble time due to gravitational wave radiation. Thus they are potential
sources for ground-based gravitational wave detectors. We estimate the yearly
detection rate for current and advanced ground-based detectors and find a
modest enhancement over the rate predicted for binaries produced by pure
stellar evolution in galactic fields. We also find that many of the ejected
binaries will pass through the longer wavelength Laser Interferometer Space
Antenna (LISA) band and may be individually resolvable. We find a low
probability that the Galaxy will contain a binary in the LISA band during its
three-year mission. Some such binaries may, however, be detectable at Mpc
distances implying that there may be resolvable stellar-mass LISA sources
beyond our Galaxy. We conclude that globular clusters have a significant effect
on the detection rate of ground-based detectors and may produce interesting
LISA sources in local group galaxies.Comment: 19 pages, 16 figures, 2 tables, submitted to MNRA
The origin of the first neutron star -- neutron star merger
The first neutron star-neutron star (NS-NS) merger was discovered on August
17, 2017 through gravitational waves (GW170817) and followed with
electromagnetic observations. This merger was detected in an old elliptical
galaxy with no recent star formation. We perform a suite of numerical
calculations to understand the formation mechanism of this merger. We probe
three leading formation mechanisms of double compact objects: classical
isolated binary star evolution, dynamical evolution in globular clusters and
nuclear cluster formation to test whether they are likely to produce NS-NS
mergers in old host galaxies. Our simulations with optimistic assumptions show
current NS-NS merger rates at the level of 10^-2 yr^-1 from binary stars, 5 x
10^-5 yr^-1 from globular clusters and 10^-5 yr^-1 from nuclear clusters for
all local elliptical galaxies (within 100 Mpc^3). These models are thus in
tension with the detection of GW170817 with an observed rate 1.5 yr^-1 (per 100
Mpc^3; LIGO/Virgo estimate). Our results imply that either (i) the detection of
GW170817 by LIGO/Virgo at their current sensitivity in an elliptical galaxy is
a statistical coincidence; or that (ii) physics in at least one of our three
models is incomplete in the context of the evolution of stars that can form
NS-NS mergers; or that (iii) another very efficient (unknown) formation channel
with a long delay time between star formation and merger is at play.Comment: A&A: accepte
Gravitational Radiation From Globular Clusters
Space-based gravitational wave detectors will have the ability to observe
continuous low frequency gravitational radiation from binary star systems. They
can determine the direction to continuous sources with an angular resolution
approaching tens of arcminutes. This resolution should be sufficient to
identify binary sources as members of some nearby globular clusters. Thus,
gravitational radiation can be used to determine the population of hard
binaries in globular clusters. For particularly hard binaries, the orbital
period may change as a result of gravitational wave emission. If one of these
binaries can be identified with a globular cluster, then the distance to that
cluster can be determined. Thus, gravitational radiation may provide
reddening-independent distance measurements to globular clusters.Comment: 26 pages, 1 figure, LaTeX, uses aasms4.sty, submitted to Ap.
Inspiralling compact binaries in quasi-elliptical orbits: The complete third post-Newtonian energy flux
The instantaneous contributions to the 3PN gravitational wave luminosity from
the inspiral phase of a binary system of compact objects moving in a quasi
elliptical orbit is computed using the multipolar post-Minkowskian wave
generation formalism. The necessary inputs for this calculation include the 3PN
accurate mass quadrupole moment for general orbits and the mass octupole and
current quadrupole moments at 2PN. Using the recently obtained 3PN
quasi-Keplerian representation of elliptical orbits the flux is averaged over
the binary's orbit. Supplementing this by the important hereditary
contributions arising from tails, tails-of-tails and tails squared terms
calculated in a previous paper, the complete 3PN energy flux is obtained. The
final result presented in this paper would be needed for the construction of
ready-to-use templates for binaries moving on non-circular orbits, a plausible
class of sources not only for the space based detectors like LISA but also for
the ground based ones.Comment: 40 pages. Minor changes in text throughout. Minor typos in Eqs.
(3.3b), (7.7f), (8.19d) and (8.20) corrected. Matches the published versio
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
Third post-Newtonian angular momentum flux and the secular evolution of orbital elements for inspiralling compact binaries in quasi-elliptical orbits
The angular momentum flux from an inspiralling binary system of compact
objects moving in quasi-elliptical orbits is computed at the third
post-Newtonian (3PN) order using the multipolar post-Minkowskian wave
generation formalism. The 3PN angular momentum flux involves the instantaneous,
tail, and tail-of-tails contributions as for the 3PN energy flux, and in
addition a contribution due to non-linear memory. We average the angular
momentum flux over the binary's orbit using the 3PN quasi-Keplerian
representation of elliptical orbits. The averaged angular momentum flux
provides the final input needed for gravitational wave phasing of binaries
moving in quasi-elliptical orbits. We obtain the evolution of orbital elements
under 3PN gravitational radiation reaction in the quasi-elliptic case. For
small eccentricities, we give simpler limiting expressions relevant for phasing
up to order . This work is important for the construction of templates for
quasi-eccentric binaries, and for the comparison of post-Newtonian results with
the numerical relativity simulations of the plunge and merger of eccentric
binaries.Comment: 62 pages, 18 figures, matches with the published versio
All-Sky LIGO Search for Periodic GravitationalWaves in the Early Fifth-Science-Run Data
We report on an all-sky search with the LIGO detectors for periodic gravitational waves in the frequency range 50–1100 Hz and with the frequency’s time derivative in the range −5×10−9–0 Hz s−1. Data from the first eight months of the fifth LIGO science run (S5) have been used in this search, which is based on a semicoherent method (PowerFlux) of summing strain power. Observing no evidence of periodic gravitational radiation, we report 95% confidence-level upper limits on radiation emitted by any unknown isolated rotating neutron stars within the search range. Strain limits below 10−24 are obtained over a 200-Hz band, and the sensitivity improvement over previous searches increases the spatial volume sampled by an average factor of about 100 over the entire search band. For a neutron star with nominal equatorial ellipticity of 10−6, the search is sensitive to distances as great as 500 pc
Search for gravitational wave ringdowns from perturbed black holes in LIGO S4 data
According to general relativity a perturbed black hole will settle to a stationary configuration by the emission of gravitational radiation. Such a perturbation will occur, for example, in the coalescence of a black hole binary, following their inspiral and subsequent merger. At late times the waveform is a superposition of quasinormal modes, which we refer to as the ringdown. The dominant mode is expected to be the fundamental mode, l=m=2. Since this is a well-known waveform, matched filtering can be implemented to search for this signal using LIGO data. We present a search for gravitational waves from black hole ringdowns in the fourth LIGO science run S4, during which LIGO was sensitive to the dominant mode of perturbed black holes with masses in the range of 10M⊙ to 500M⊙, the regime of intermediate-mass black holes, to distances up to 300 Mpc. We present a search for gravitational waves from black hole ringdowns using data from S4. No gravitational wave candidates were found; we place a 90%-confidence upper limit on the rate of ringdowns from black holes with mass between 85M⊙ and 390M⊙ in the local universe, assuming a uniform distribution of sources, of 3.2×10−5 yr−1 Mpc−3=1.6×10−3 yr−1L−110,where L10 is 1010 times the solar blue-light luminosity
Search for gravitational waves from low mass compact binary coalescence in 186 days of LIGO’s fifth science run
We report on a search for gravitational waves from coalescing compact binaries, of total mass between 2 and 35M⊙, using LIGO observations between November 14, 2006 and May 18, 2007. No gravitational-wave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total mass. The LIGO cumulative 90%-confidence rate upper limits of the binary coalescence of neutron stars, black holes and black hole-neutron star systems are 1.4×10−2, 7.3×10−4 and 3.6×10−3 yr−1 L−110, respectively, where L10 is 1010 times the blue solar luminosity
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