(SPH) Simulations of Binary Neutron Star Coalescence Examining the Mass Ratio Dependence of Post-Newtonian Smoothed Particle Hydrodynamics Jonathon Meyers, Yi Mei, Rick Hallett, Margie Michna Advisor: Dr. Aaron Warren 2012 Purdue University North Central

Goals? What are gravity waves? Gravity waves are ripples in the curvature of spacetime which propagate as a wave, travelling outward from the source. 2 Neutron Stars (NS) coalescing Ripple in space time Black Holes What can we learn from them? Gravity is treated as a phenomenon resulting in the curvature of spacetime. When gravitational radiation pass a distant observer, that observer will find spacetime distorted by the effects of strain. Hypothesized that they will be able to provide observers on Earth with information about neutron stars, black holes, and related phenomena such as gamma-ray bursts.

Hulse-Taylor PSR Discovered by Russell Alan Hulse and Joseph Hooton Taylor, Jr. in 1974 Two radiating NS orbiting around a common center of mass, forming a binary star system. The two NS lose energy in accordance with GW Taylor Hulse

What is “SPH”? Hydrodynamics is important when tidal effects become significant near end of coalescence. SPH simulates fluids as a set of particles. Forces are calculated on each particle, and velocity/position updated at each time step. A smoothing function interpolates particle property values (such as density) to points between the particles. What is “Post-Newtonian”? In weak gravity fields, relativistic corrections to Newtonian gravity are small and can be represented as an infinite series. StarCrash keeps 1PN terms, as well as all 2.5PN terms which represent gravitational radiation reaction.

Leading Lagging

q = 0.90 q = 1.00 q = 0.90

Wavelet transforms enable time-dependent characterization of a signal, unlike traditional Fourier transforms Build signal from copies of a wavelet, where copies may be translated in time and scaled. Scale ~ frequency. We used the analytic Morlet wavelet

Primary wave frequencies similar for all q Find local maxima of CWT coefficients ~650 Hz for late inspiral & ringdown ~2000 Hz during chirp Calculate power spectrum, very weak mass dependence Would not have detected with LIGO S6 at 100 MPc.

Least-squares fit with polynomial, residuals tested for normality.

Extend simulations to cover a greater range of the parameter space; determine how the gravitational wave characteristics depend on these parameters. Gamma Mass Ratio Synchronized vs Irrotational orbits Estimate which remnants are likely to form black holes or hypermassive neutron stars. Model candidate regions in parameter space using a numerical relativity code, compare with post-Newtonian results.