Dissertation
STUDIES OF POST-MERGER BLACK HOLES, NEUTRON STARS AND DISKS: STABILITY AND ELECTROMAGNETIC SIGNALS
Doctor of Philosophy (PhD), Washington State University
2026
Abstract
Binary neutron star (BNS) mergers undergoing prompt collapse and black hole neutron star (BHNS) mergers in which the neutron star is tidally disrupted before the plunge produce black hole-accretion disk systems. On the other hand, BNS mergers that undergo delayed collapse produce hypermassive neutron stars (HMNS) as an intermediate remnant before collapsing into black holes. The post-merger systems are important for gravitational wave emissions, electromagnetic counterparts and heavy element formation. We study the stability of these post-merger HMNS systems. We validate the turning point criterion for differentially rotating realistic post-merger-like stars. We find that the conformal flatness approximation for highly differentially rotating toroidal star simulations is not a reliable approximation. We also analyze the energy deposition from neutrino pair annihilation for both general relativity (GR) and beyond GR theories for post-merger black holes. We find the energies can be sufficient for certain low-energy short gamma-ray bursts. Finally, we investigate the advantage and importance of different neutrino treatments in the post-merger phase. We find that an energy-dependent two moment closure scheme is important to consider for analysis of r-process yields, ejecta composition and kilonovae signals. We also show that inelastic neutrino-electron scattering in simulations of hypermassive neutron stars is important for simulations of hypermassive neutron stars, particularly for disk properties and neutrino luminosities.
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Details
- Title
- STUDIES OF POST-MERGER BLACK HOLES, NEUTRON STARS AND DISKS: STABILITY AND ELECTROMAGNETIC SIGNALS
- Creators
- Nishad Muhammed
- Contributors
- Matthew D Duez (Advisor)Sukanta Bose (Committee Member)Vivienne Baldassare (Committee Member)Guy Worthey (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Department of Physics and Astronomy
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 142
- Identifiers
- 99901421005001842
- Language
- English
- Resource Type
- Dissertation