55 research outputs found
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
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
Second-order parametrized-post-Newtonian Lagrangian
A many-body Lagrangian to second post-Newtonian order using an extension of the parametrized-post-Newtonian (PPN) formalism is introduced and the properties of new parameters are explored. A parametrized gauge transformation is developed to permit comparison with theories of gravity in a variety of different coordinate systems. A procedure to impose Lorentz invariance on a general second-order post-Newtonian Lagrangian is developed. The Lagrangian is then constrained to possess Lorentz invariance and a Lorentz-invariant gauge is introduced. The constrained Lagrangian is found to be described by ten new second-order PPN parameters. When the Lagrangian is further constrained to describe theories of gravity for which test particles move along geodesics, one of the ten new parameters is given entirely in terms of first-order PPN parameters, leaving only nine PPN parameters to describe the second-order gravitational interaction. A metric gauge is introduced which allows the metric to be easily found from the Lagrangian and is shown to reduce to the gauge associated with the canonical formalism of Arnowitt, Deser, and Misner when the general-relativity values of the PPN parameters are used
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
Tackling gravity wave confusion noise with template optimizers
The Mock LISA Data Challenge 4.0 simulated the joint two-year recording of gravitational wave signals from mergers of spinning black holes, extreme mass ratio inspirals, Galactic white dwarf binaries, bursts from cosmic strings, and a stochastic background—all over LISA instrument noise. We analysed this data using a global multi-start box and bound optimization scheme, incorporating multi-dimensional Nelder Mead simplex 2 optimization. Our scheme identified 2658 binaries. Of these, 2246 were found to systematically decompose the power in a strong spinning black hole merger into a white dwarf binary transform . The remaining 416 binaries were identified with a false alarm rate of ~ 23%
Double neutron stars: merger rates revisited
We revisit double neutron star (DNS) formation in the classical binary evolution scenario in light of the recent Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo DNS detection (GW170817). The observationally estimated Galactic DNS merger rate of RMW = 21+28 −14 Myr−1, based on three Galactic DNS systems, fully supports our standard input physics model with RMW = 24 Myr−1. This estimate for the Galaxy translates in a non-trivial way (due to cosmological evolution of progenitor stars in chemically evolving Universe) into a local (z ≈ 0) DNS merger rate density of Rlocal = 48 Gpc−3 yr−1, which is not consistent with the current LIGO/Virgo DNS merger rate estimate (1540+3200 −1220 Gpc−3 yr−1). Within our study of the parameter space, we find solutions that allow for DNS merger rates as high as Rlocal ≈ 600+600 −300 Gpc−3 yr−1 which are thus consistent with the LIGO/Virgo estimate. However, our corresponding BH–BH merger rates for the models with high DNS merger rates exceed the current LIGO/Virgo estimate of local BH–BH merger rate (12–213 Gpc−3 yr−1). Apart from being particularly sensitive to the common envelope treatment, DNS merger rates are rather robust against variations of several of the key factors probed in our study (e.g. mass transfer, angular momentum loss, and natal kicks). This might suggest that either common envelope development/survival works differently for DNS (∼10–20M stars) than for BH–BH (∼40–100M stars) progenitors, or high black hole (BH) natal kicks are needed to meet observational constraints for both types of binaries. Our conclusion is based on a limited number of (21) evolutionary models and is valid within this particular DNS and BH–BH isolated binary formation scenario
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
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