Benjamin D. Lackey

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

Tidal deformability of neutron stars with realistic equations of state and their gravitational wave signatures in binary inspiral

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Extracting equation of state parameters from black hole-neutron star mergers. I. Nonspinning black holes

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.

Extracting equation of state parameters from black hole-neutron star mergers: aligned-spin black holes and a preliminary waveform model

The early part of the gravitational wave signal of binary neutron-star inspirals can potentially yield robust information on the nuclear equation of state. The influence of a stars internal structure on the waveform is characterized by a single parameter: the tidal deformability {lambda}, which measures the stars quadrupole deformation in response to the companions perturbing tidal field. We calculate {lambda} for a wide range of equations of state and find that the value of {lambda} spans an order of magnitude for the range of equation of state models considered. An analysis of the feasibility of discriminating between neutron-star equations of state with gravitational wave observations of the early part of the inspiral reveals that the measurement error in {lambda} increases steeply with the total mass of the binary. Comparing the errors with the expected range of {lambda}, we find that Advanced LIGO observations of binaries at a distance of 100 Mpc will probe only unusually stiff equations of state, while the proposed Einstein Telescope is likely to see a clean tidal signature.

Reconstructing the neutron-star equation of state with gravitational-wave detectors from a realistic population of inspiralling binary neutron stars

The late inspiral, merger, and ringdown of a black hole-neutron star (BHNS) system can provide information about the neutron-star equation of state (EOS). Candidate EOSs can be approximated by a parametrized piecewise-polytropic EOS above nuclear density, matched to a fixed low-density EOS; and we report results from a large set of BHNS inspiral simulations that systematically vary two parameters. To within the accuracy of the simulations, we find that, apart from the neutron-star mass, a single physical parameter Lambda, describing its deformability, can be extracted from the late inspiral, merger, and ringdown waveform. This parameter is related to the radius, mass, and l=2 Love number, k_2, of the neutron star by Lambda = 2k_2 R^5/3M_{NS}^5, and it is the same parameter that determines the departure from point-particle dynamics during the early inspiral. Observations of gravitational waves from BHNS inspiral thus restrict the EOS to a surface of constant Lambda in the parameter space, thickened by the measurement error. Using various configurations of a single Advanced LIGO detector, we find that neutron stars are distinguishable from black holes of the same mass and that Lambda^{1/5} or equivalently R can be extracted to 10-40% accuracy from single events for mass ratios of Q=2 and 3 at a distance of 100 Mpc, while with the proposed Einstein Telescope, EOS parameters can be extracted to accuracy an order of magnitude better.

Systematic and statistical errors in a Bayesian approach to the estimation of the neutron-star equation of state using advanced gravitational wave detectors

Information about the neutron-star equation of state is encoded in the waveform of a black hole-neutron star system through tidal interactions and the possible tidal disruption of the neutron star. During the inspiral this information depends on the tidal deformability

A census of quasar-intrinsic absorption in the Hubble Space Telescope archive: systems from high-resolution echelle spectra

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Gravitational-wave cutoff frequencies of tidally disruptive neutron star-black hole binary mergers

of the neutron star, and we find that the best-measured parameter during the merger and ringdown is consistent with

Aligned spin neutron star-black hole mergers: A gravitational waveform amplitude model

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Neutron star equation of state via gravitational wave observations

as well. We performed 134 simulations where we systematically varied the equation of state as well as the mass ratio, neutron star mass, and aligned spin of the black hole. Using these simulations we develop an analytic representation of the full inspiral-merger-ringdown waveform calibrated to these numerical waveforms; we use this analytic waveform and a Fisher matrix analysis to estimate the accuracy to which