B. J. Owen

Gravitational waves from hot young rapidly rotating neutron stars

Gravitational radiation drives an instability in the r-modes of young rapidly rotating neutron stars. This instability is expected to carry away most of the angular momentum of the star by gravitational radiation emission, leaving a star rotating at about 100 Hz. In this paper we model in a simple way the development of the instability and evolution of the neutron star during the year-long spindown phase. This allows us to predict the general features of the resulting gravitational waveform. We show that a neutron star formed in the Virgo cluster could be detected by the LIGO and VIRGO gravitational wave detectors when they reach their “enhanced” level of sensitivity, with an amplitude signal-to-noise ratio that could be as large as about 8 if near-optimal data analysis techniques are developed. We also analyze the stochastic background of gravitational waves produced by the r-mode radiation from neutron-star formation throughout the universe. Assuming a substantial fraction of neutron stars are born with spin frequencies near their maximum values, this stochastic background is shown to have an energy density of about 10^(−9) of the cosmological closure density, in the range 20 Hz to 1 kHz. This radiation should be detectable by “advanced” LIGO as well.

Gravitational radiation instability in hot young neutron stars

We show that gravitational radiation drives an instability in hot young rapidly rotating neutron stars. This instability occurs primarily in the l=2 r-mode and will carry away most of the angular momentum of a rapidly rotating star by gravitational radiation. On the timescale needed to cool a young neutron star to about T=10^9 K (about one year) this instability can reduce the rotation rate of a rapidly rotating star to about 0.076\Omega_K, where \Omega_K is the Keplerian angular velocity where mass shedding occurs. In older colder neutron stars this instability is suppressed by viscous effects, allowing older stars to be spun up by accretion to larger angular velocities.

The GEO 600 gravitational wave detector

The GEO 600 laser interferometer with 600 m armlength is part of a worldwide network of gravitational wave detectors. Due to the use of advanced technologies like multiple pendulum suspensions with a monolithic last stage and signal recycling, the anticipated sensitivity of GEO 600 is close to the initial sensitivity of detectors with several kilometres armlength. This paper describes the subsystems of GEO 600, the status of the detector by September 2001 and the plans towards the first science run.

Matched filtering of gravitational waves from inspiraling compact binaries: Computational cost and template placement.

We estimate the number of templates, computational power, and storage required for a one-step matched filtering search for gravitational waves from inspiraling compact binaries. Our estimates for the one-step search strategy should serve as benchmarks for the evaluation of more sophisticated strategies such as hierarchical searches. We use a discrete family of two-parameter wave form templates based on the second post-Newtonian approximation for binaries composed of nonspinning compact bodies in circular orbits. We present estimates for all of the large- and mid-scale interferometers now under construction: LIGO ~three configurations!, VIRGO, GEO600, and TAMA. To search for binaries with components more massive than mmin50.2M( while losing no more than 10% of events due to coarseness of template spacing, the initial LIGO interferometers will require about 1.0310 11 flops ~floating point operations per second ! for data analysis to keep up with data acquisition. This is several times higher than estimated in previous work by Owen, in part because of the improved family of templates and in part because we use more realistic ~higher! sampling rates. Enhanced LIGO, GEO600, and TAMA will require computational power similar to initial LIGO. Advanced LIGO will require 7.8310 11 flops, and VIRGO will require 4.8 310 12 flops to take full advantage of its broad target noise spectrum. If the templates are stored rather than generated as needed, storage requirements range from 1.5 310 11 real numbers for TAMA to 6.2310 14 for VIRGO. The computational power required scales roughly as mmin8/3 and the storage as mmin13/3 . Since these scalings are perturbed by the curvature of the parameter space at second post-Newtonian order, we also provide estimates for a search with mmin51M( . Finally, we sketch and discuss an algorithm for placing the templates in the parameter space. @S0556-2821~99!05214-5#

Constraints on a phenomenologically parametrized neutron-star equation of state

We introduce a parametrized high-density equation of state (EOS) in order to systematize the study of constraints placed by astrophysical observations on the nature of neutron-star matter. To obtain useful constraints, the number of parameters must be smaller than the number of EOS-related neutron-star properties measured, but large enough to accurately approximate the large set of candidate EOSs. We find that a parametrized EOS based on piecewise polytropes with 3 free parameters matches, to about 4% rms error, an extensive set of candidate EOSs at densities below the central density of

Maximum elastic deformations of compact stars with exotic equations of state

1.4{M}_{\ensuremath{\bigodot}}

Effect of hyperon bulk viscosity on neutron-star r-modes

stars. Adding observations of more massive stars constrains the higher-density part of the EOS and requires an additional parameter. We obtain constraints on the allowed parameter space set by causality and by present and near-future astronomical observations with the least model dependence. Stringent constraints on the EOS parameter space are associated with the future measurement of the moment of inertia of PSR J0737-3039A combined with the maximum known neutron-star mass. We also present in an appendix a more efficient algorithm than has previously been used for finding points of marginal stability and the maximum angular velocity of stable stars.

Gravitational field and equations of motion of spinning compact binaries to 2.5 post-Newtonian order

I make the first estimates of maximum elastic quadrupole deformations sustainable by alternatives to conventional neutron stars. Solid strange quark stars might sustain maximum ellipticities (dimensionless quadrupoles) up to a few times rather than a few times for conventional neutron stars, and hybrid quark-baryon or meson-condensate stars might sustain up to . Most of the difference is due to the shear modulus, which can be up to rather than in the inner crust of a conventional neutron star. Maximum solid strange star ellipticities are comparable to upper limits obtained for several known pulsars in a recent gravitational-wave search by LIGO. Maximum ellipticities of the more robust hybrid model will be detectable by LIGO at initial design sensitivity. A large shear modulus also strengthens the case for starquakes as an explanation for frequent pulsar glitches.

Lattice QCD evidence that the Λ(1405) resonance is an antikaon-nucleon molecule.

Neutron stars are expected to contain a significant number of hyperons in addition to protons and neutrons in the highest density portions of their cores. Following the work of Jones, we calculate the coefficient of bulk viscosity due to nonleptonic weak interactions involving hyperons in neutron-star cores, including new relativistic and superfluid effects. We evaluate the influence of this new bulk viscosity on the gravitational radiation driven instability in the r-modes. We find that the instability is completely suppressed in stars with cores cooler than a few times 10 9 K, but that stars rotating more rapidly than 10‐30% of maximum are unstable for temperatures around 10 10 K. Since neutron-star cores are expected to cool to a few times 10 9 K within seconds ~much shorter than the r-mode instability growth time! due to direct Urca processes, we conclude that the gravitational radiation instability will be suppressed in young neutron stars before it can significantly change the angular momentum of the star.

Observational constraints on hyperons in neutron stars

We derive spin-orbit coupling effects on the gravitational field and equations of motion of compact binaries in the 2.5 post-Newtonian approximation to general relativity, one PN order beyond where spin effects first appear. Our method is based on that of Blanchet, Faye, and Ponsot, who use a post-Newtonian metric valid for general (continuous) fluids and represent pointlike compact objects with a