Periodic Gravitational Radiation from Neutron Stars with Exotic Matter

Open Access
Author:
Nayyar, Mohit
Graduate Program:
Physics
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
March 08, 2007
Committee Members:
  • Benjamin J Owen, Committee Chair
  • Stephane Coutu, Committee Member
  • Pablo Laguna, Committee Member
  • George Pavlov, Committee Member
Keywords:
  • neutron stars
  • r-modes
  • gravitational radiation
  • equation of state
  • hybrid stars
  • LMXBs
Abstract:
The first generation of interferometric gravitational wave detectors is now in operation and actively searching the skies for gravitational waves. The sources that may be detected include rotating neutron stars, especially if they contain some matter more exotic than neutrons. This thesis investigates issues related to two probable mechanisms for the generation of gravitational radiation from neutron stars containing exotic states of matter. The first is the persistent gravitational radiation from $r$-mode oscillations in accreting neutron stars containing hyperons, while the second is the gravitational radiation from large elastic deformations in quark-baryon hybrid stars. Before examining two mechanisms for gravitational radiation generation, we address the neutron star equation of state that forms the basis of any neutron star calculation. To ensure the validity of equations of state used in later sections of the thesis, we constrain a set of relativistic mean field equations of state using the latest neutron star observations. We find that, of these equations of state, only the stiffest previously used in literature satisfy the constraints. We therefore generate new equations of state within the same relativistic mean field framework. Persistent gravitational radiation caused by $r$-modes could explain why neutron stars in low mass x-ray binaries (LMXBs) are not being spun up by accretion. A high duty cycle of gravitational radiation is only possible when the cores of these stars contain some exotic state of matter. We examine the scenario for persistent emission for a set of equations of state that allow for the presence of hyperons, and find that persistent emission is robust. Therefore, gravitational radiation from neutron stars in LMXBs is likely to be detectable by advanced gravitational wave detectors if they contain exotic matter. The spindown for the Crab pulsar suggests that it could be detectable by the first generation of interferometric gravitational wave detectors if much of the spindown is due to gravitational wave emission. Conventional neutron stars cannot support quadrupole moments large enough to generate gravitational radiation commensurate with the Crab pulsar spindown. This warrants the study of other classes of neutron stars containing exotic matter which could display higher quadrupole moments. We, therefore, evaluate the maximum quadrupole moments of a class of baryon-quark hybrid stars. We find that the maximum quadrupole moments are just below the threshold for being detectable by the present generation of detectors, but are good prospects for the next generation.