334 research outputs found
Detecting Eccentric Globular Cluster Binaries with LISA
The energy carried in the gravitational wave signal from an eccentric binary
is spread across several harmonics of the orbital frequency. The inclusion of
the harmonics in the analysis of the gravitational wave signal increases the
signal-to-noise ratio of the detected signal for binaries whose fundamental
frequency is below the galactic confusion-limited noise cut-off. This can allow
for an improved angular resolution for sources whose orbital period is greater
than 2000 s. Globular cluster sources include possible binary black holes and
neutron stars which may have high eccentricities. Cluster dynamics may also
enhance the eccentricities of double white dwarf binaries and white
dwarf-neutron star binaries over the galactic sources. Preliminary results of
the expected signal-to-noise ratio for selected globular cluster binaries are
presented.Comment: 3 pages, 2 figures, to be published in proceedings of 20th Texas
Symposium. Requires aipproc.sty (included
Tidal Perturbations to the Gravitational Inspiral of J0651+2844
The recently discovered J0651+2844 is a detached, eclipsing white dwarf
binary with an orbital period of 765 s. We investigate the prospects for the
detection of gravitational radiation from this system and estimate the effect
of the tidal deformation of the low-mass component on the period evolution of
the system. Because of the high inclination of the system, the amplitude of the
gravitational waves at Earth will be as much as a factor of two lower than that
from an optimally oriented system. The dominant contribution of tidal
corrections to the period evolution comes from the increase in rotational
energy of the components as they spin up to remain tied to the orbital period.
This contribution results in an advance of the timing of the eclipses by an
additional 0.3 s after one year.Comment: 5 pages, submitted to ApJ
Gravitational Radiation from Black Hole Binaries in Globular Clusters
A populations of stellar mass black hole binaries may exist in globular
clusters. The dynamics of globular cluster evolution imply that there may be at
most one black hole binary is a globular cluster. The population of binaries
are expected to have orbital periods greater than a few hours and to have a
thermal distribution of eccentricities. In the LISA band, the gravitational
wave signal from these binaries will consist of several of the higher harmonics
of the orbital frequency. A Monte Carlo simulation of the galactic globular
cluster system indicates that LISA will detect binaries in 10 % of the clusters
with an angular resolution sufficient to identify the host cluster of the
binary.Comment: 7 pages, 2 eps figures, uses iopart styl
Double Compact Objects as Low-frequency Gravitational Wave Sources
We study the Galactic field population of double compact objects (NS-NS,
BH-NS, BH-BH binaries) to investigate the number (if any) of these systems that
can potentially be detected with LISA at low gravitational-wave frequencies. We
calculate the Galactic numbers and physical properties of these binaries and
show their relative contribution from the disk, bulge and halo. Although the
Galaxy hosts 10^5 double compact object binaries emitting low-frequency
gravitational waves, only a handful of these objects in the disk will be
detectable with LISA, but none from the halo or bulge. This is because the bulk
of these binaries are NS-NS systems with high eccentricities and long orbital
periods (weeks/months) causing inefficient signal accumulation (small number of
signal bursts at periastron passage in 1 yr of LISA observations) rendering
them undetectable in the majority of these cases. We adopt two evolutionary
models that differ in their treatment of the common envelope phase that is a
major (and still mostly unknown) process in the formation of close double
compact objects. Depending on the adopted evolutionary model, our calculations
indicate the likely detection of about 4 NS-NS binaries and 2 BH-BH systems
(model A; likely survival of progenitors through CE) or only a couple of NS-NS
binaries (model B; suppression of the double compact object formation due to CE
mergers).Comment: 12 pages, ApJ accepted, major change
Relativistic binaries in globular clusters
The galactic population of globular- cluster\u27s are old, dense star systems, with a typical cluster containing 104 -107 stars. As an old population of stars, globular clusters contain many collapsed and degenerate objects. As a dense population of stars, globular clusters are the scene of many interesting close dynamical interactions between stars. These dynamical interactions can alter the evolution of individual stars and can produce tight binary systems containing one or- two compact objects. In this review, we discuss the theoretical models of globular cluster evolution and binary evolution, techniques for simulating this evolution which lead to relativistic binaries, and current and possible future observational evidence for this population. Globular cluster evolution will focus on the properties that boost the production of hard binary systems and on the tidal interactions of the galaxy with the cluster, which tend to alter the structure of the globular cluster with time. The interaction of the components of hard binary systems alters the evolution of both bodies and can lead to exotic objects. Direct Ar-body integrations and Fokker-Planck simulations of the evolution of globular clusters that incorporate tidal interactions and lead to predictions of relativistic binary populations are also discussed. We discuss the current observational evidence for cataclysmic variables, millisecond pulsars, and low-mass X-ray binaries as well as possible future detection of relativistic binaries with gravitational radiation. © Max Planck Society and the authors
Prospects for Detection of Extragalactic Stellar Black Hole Binaries in the Nearby Universe
Stellar mass black hole binaries have individual masses between 10-80 solar
masses. These systems may emit gravitational waves at frequencies detectable at
Megaparsec distances by space-based gravitational wave observatories. In a
previous study, we determined the selection effects of observing these systems
with detectors similar to the Laser Interferometer Space Antenna by using a
generated population of binary black holes that covered a reasonable parameter
space and calculating their signal-to-noise ratio. We further our study by
populating the galaxies in our nearby (less than 30 Mpc) universe with binary
black hole systems drawn from a distribution found in the Synthetic Universe to
ultimately investigate the likely event rate of detectable binaries from
galaxies in the nearby universe.Comment: Proceedings of LISA 1
The LISA Gravitational Wave Foreground: A Study of Double White Dwarfs
Double white dwarfs are expected to be a source of confusion-limited noise
for the future gravitational wave observatory LISA. In a specific frequency
range, this 'foreground noise' is predicted to rise above the instrumental
noise and hinder the detection of other types of signals, e.g., gravitational
waves arising from stellar mass objects inspiraling into massive black holes.
In many previous studies only detached populations of compact object binaries
have been considered in estimating the LISA gravitational wave foreground
signal. Here, we investigate the influence of compact object detached and
Roche-Lobe Overflow Galactic binaries on the shape and strength of the LISA
signal. Since >99% of remnant binaries which have orbital periods within the
LISA sensitivity range are white dwarf binaries, we consider only these
binaries when calculating the LISA signal. We find that the contribution of
RLOF binaries to the foreground noise is negligible at low frequencies, but
becomes significant at higher frequencies, pushing the frequency at which the
foreground noise drops below the instrumental noise to >6 mHz. We find that it
is important to consider the population of mass transferring binaries in order
to obtain an accurate assessment of the foreground noise on the LISA data
stream. However, we estimate that there still exists a sizeable number (~11300)
of Galactic double white dwarf binaries which will have a signal-to-noise ratio
>5, and thus will be potentially resolvable with LISA. We present the LISA
gravitational wave signal from the Galactic population of white dwarf binaries,
show the most important formation channels contributing to the LISA disc and
bulge populations and discuss the implications of these new findings.Comment: ApJ accepted. 28 pages, 11 figures (low resolution), 5 tables, some
new references and changed content since last astro-ph versio
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