Neutron stars in compact binary systems: From the equation of state to gravitational radiation
Abstract
Neutron stars are incredibly dense astrophysical objects that give a unique glimpse of physics at extreme scales. This thesis examines computational and mathematical methods of translating our theoretical understanding of neutron star physics, from the properties of matter to the relativistic behaviour of binary systems, into observable characteristics of astrophysical neutron stars.
The properties of neutron star matter are encoded in the equation of state, which has substantial uncertainty. Many equations of state have been proposed based on different models of the underlying physics. These predict various quantities, such as the maximum stable mass, which allow them to be ruled out by astronomical measurements. This thesis presents a natural way to write a general equation of state that can approximate many different candidate equations of state with a few parameters. Astronomical observations are then used to systematically constrain parameter values, instead of ruling out models on a case-by-case basis. Orbiting pairs of neutron stars will release gravitational radiation and spiral in toward each other. The radiation may be observable with ground-based detectors. Until the stars get very close to each other the rate of inspiral is slow, and the orbits are approximately circular. One can numerically find spacetime solutions that satisfy the full set of Einstein equations by imposing an exact helical symmetry. However, we find that the helically-symmetric solution must be matched to a waveless boundary region to achieve convergence. Work with toy models suggests this lack of convergence is intractable, but the agreement of waveless and helical codes validates the use of either approximation to construct state-of-the-art initial data for fully dynamic binary neutron star simulations. The parameterized equation of state can be used with such numerical simulations to systematically explore how the emitted gravitational waves depend on the properties of neutron star matter. Late-time waveforms from numerical simulations with varying equation of state are matched onto early-time post- Newtonian waveforms to generate hybrid waveforms for data analysis. The variation in waveforms from changing the EOS is compared to the noise properties of the tunable Advanced LIGO detector to determine measurability of neutron star and equation of state parameters.- Publication:
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Ph.D. Thesis
- Pub Date:
- 2008
- Bibcode:
- 2008PhDT........15R
- Keywords:
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- Neutron stars;
- Equation of state;
- Gravitational radiation