(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
Slide 2
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.
Slide 3
Hulse-Taylor PSR1913+16 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
Slide 4
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.
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Leading Lagging
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q = 0.90 q = 1.00 q = 0.90
Slide 9
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
Slide 10
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.
Slide 11
Least-squares fit with polynomial, residuals tested for
normality.
Slide 12
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.