Browsing by Author "Chatziioannou, Katerina"

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Analytic Gravitational Waveforms for Generic Precessing Binary Inspirals
(2017-02) Chatziioannou, Katerina; Klein, Antoine; Cornish, Neil J.; Yunes, Nicolás
Binary systems of two compact objects circularize and spiral toward each other via the emission of gravitational waves. The coupling of the spins of each object with the orbital angular momentum causes the orbital plane to precess, which leads to modulation of the gravitational wave signal. Until now, generating frequency-domain waveforms for fully precessing systems for use in gravitational wave data analysis meant numerically integrating the equations of motion, then Fourier transforming the result, which is very computationally intensive for systems that complete hundreds or thousands of cycles in the sensitive band of a detector. Previously, analytic solutions were only available for certain special cases or for simplified models. Here we describe the construction of closed-form, frequency-domain waveforms for fully-precessing, quasi-circular binary inspirals.
Improved next-to-leading order tidal heating and torquing of a Kerr black hole
(2016-10) Chatziioannou, Katerina; Poisson, Eric; Yunes, Nicolás
We calculate the energy and angular-momentum fluxes across the event horizon of a tidally deformed, rapidly rotating black hole to next-to-leading order in the curvature of the external spacetime. These are expressed in terms of tidal quadrupole moments and their time derivatives, which provide a characterization of a generic tidal environment. As an application of our results, we provide an expression for the energy and angular-momentum fluxes across the horizon when the black hole is a member of a binary system on a slowly moving, quasicircular orbit. Our expressions are accurate to 1.5 post-Newtonian order beyond the leading-order fluxes, but they are valid for arbitrary mass ratios. We compare our results to those previously obtained in the case of an extreme mass ratio binary, and find that they do not agree at the 1.5 post-Newtonian order. We investigate a number of possible sources for this discrepancy, but are ultimately unable to resolve it.
Probing the internal composition of neutron stars with gravitational waves
(2015-11) Chatziioannou, Katerina; Yagi, Kent; Klein, Antoine; Cornish, Neil J.; Yunes, Nicolás
Gravitational waves from neutron star binary inspirals contain information about the as yet unknown equation of state of supranuclear matter. In the absence of definitive experimental evidence that determines the correct equation of state, a number of diverse models that give the pressure inside a neutron star as function of its density have been constructed by nuclear physicists. These models differ not only in the approximations and techniques they employ to solve the many-body Schrödinger equation, but also in the internal neutron star composition they assume. We study whether gravitational wave observations of neutron star binaries in quasicircular inspirals up to contact will allow us to distinguish between equations of state of differing internal composition, thereby providing important information about the properties and behavior of extremely high density matter. We carry out a Bayesian model selection analysis, and find that second generation gravitational wave detectors can heavily constrain equations of state that contain only quark matter, but hybrid stars containing both normal and quark matter are typically harder to distinguish from normal matter stars. A gravitational wave detection with a signal-to-noise ratio of 20 and masses around 1.4M⊙ would provide indications of the existence or absence of strange quark stars, while a signal-to-noise ratio 30 detection could either detect or rule out strange quark stars with a 20 to 1 confidence. The presence of kaon condensates or hyperons in neutron star inner cores cannot be easily confirmed. For example, for the equations of state studied in this paper, even a gravitational wave signal with a signal-to-noise ratio as high as 60 would not allow us to claim a detection of kaon condensates or hyperons with confidence greater than 5 to 1. On the other hand, if kaon condensates and hyperons do not form in neutron stars, a gravitational wave signal with similar signal-to-noise ratio would be able to constrain their existence with an 11 to 1 confidence for high-mass systems. We, finally, find that combining multiple lower signal-to-noise ratio detections (stacking) must be handled with caution since it could fail in cases where the prior information dominates over new information from the data.
Spin-precessing compact binaries : gravitational wave modeling and information extraction
(Montana State University - Bozeman, College of Letters & Science, 2016) Chatziioannou, Katerina; Chairperson, Graduate Committee: Nicolas Yunes
In this dissertation we study the effect of spin-precession on gravitational waves emitted by quasicircular compact binary systems. In their most generic configuration, compact objects in a binary system are subject to interactions between the spin and the orbital angular momenta. These interactions give rise to precessional effects that add rich structure to the emitted gravitational waveforms. We study this spin-induced structure with an emphasis on extracting the information it encodes. In particular, we construct gravitational wave models that accurately capture spin-precessional effects. We then use them to study how much information relevant to astrophysics and nuclear physics we can extract from future observations of gravitational waves from compact binary coalescences.