General Relativistic Hydrodynamic Simulations of Neutron Star Mergers: From Quarks to Gravitational Waves
Open Access
- Author:
- Prakash, Aviral
- Graduate Program:
- Physics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 23, 2024
- Committee Members:
- Bangalore Sathyaprakash, Major Field Member
Steinn Sigurdsson, Outside Unit & Field Member
David Radice, Chair & Dissertation Advisor
Mauricio Terrones, Program Head/Chair
Zoltan Fodor, Major Field Member - Keywords:
- Neutron Stars
Equation of State
QCD
Phase Transitions
Gravitational Waves - Abstract:
- With the advent of gravitational wave astronomy, it has become possible to study mergers of compact objects such as neutron stars in a new window of gravitational radiation. Gravitational waves carry imprints of the nuclear makeup of these compact objects which can be revealed in a merger. Such mergers can be studied in simulations and their observations (gravitational or electromagnetic) can help constrain the available models of nuclear physics. In this dissertation, we employ general relativistic neutrino- radiation hydrodynamic simulations of mergers of neutron stars, with a particular focus on understanding QCD phase transitions to deconfined quarks. To this aim, we compute gravitational wave signatures of such phase transitions and find that they manifest as an increase in a postmerger spectral frequency of the neutron star merger remnant. This increase, however, is modest at best for the equation of state employed. Additionally, the frequencies are degenerate with merger simulations of neutron stars with exclusively nucleonic (confined quarks) degrees of freedom. We also propose a multi-modal gravitational wave signature, in that, a non-detection or a detection of a feeble one-armed spiral instability in a merger remnant could point to the presence of phase transitions. Further, we explore mergers of strange stars which are self-bound compact objects but find that the gravitational wave signatures of their mergers are difficult to distinguish from mergers of other neutron stars. We then examine thermal effects in a merger simulation of neutron stars and study their influence on the postmerger gravitational wave emission. In a Bayesian inference study, we find that at postmerger signal-to-noise ratios of 15, the next generation of gravitational wave detectors could potentially constrain such thermal effects. Next, we examine gravitational wave emission from multiple models of QCD phase transitions in a fully consistent Bayesian inference study and find that the next generation of gravitational wave detectors can reliably identify and distinguish particularly strong QCD phase transitions at postmerger signal-to-noise ratios as low as 10. Finally, we provide some important insights into how specific choices of constructions of phase transition models can manifest themselves in ways which could only be revealed in such simulations making numerical relativity an indispensable tool for the science cases of the next generation of gravitational wave detectors.