Numerical Integration for Neutron Star Binaries in Eccentric Orbits

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자연과학대학 물리·천문학부
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서울대학교 대학원
neutron stareccentric orbitinitial dataevolution
학위논문 (석사)-- 서울대학교 대학원 : 자연과학대학 물리·천문학부, 2018. 2. 이형목.
This dissertation try to focus on new paradigm of initial data and its evolution
for Einstein’s field equation when spacetime has matter field. To make proper initial
data, we carry out test employing boosted Tolmann-Oppenhiemmer-Volkoff(TOV) star.
TOV star assumes perfect fluid obeying polytropic process and metric keeps spherical
symmetry. It is static and stationary solution so it shows stable maximum density oscillation.
On the other hand, when TOV star got boosted, maximum density oscillation
become excited. Such a behaviour provide good hint for error which will arise at binary
We presents initial data for binary in the eccentric orbit employing double TOV
stars. Rotation configuration in the binary should have vanishing vorticity. To deal with
such a configuration, constant coordinate velocity approximation is utilized. Moreover,
initial external field due to companion is ignored because we want to look at contribution
of relativistic hydrodynamics part. So, metric combination is not superposition but
sewing TOV solution at the boundary line containing origin. We simply compare initial
data of us and LORENE initial data which solves constraints equations via multi grid
method. Key difference is high frequency mode of density oscillation and gravitational
wave due to surface mode of neutron star.
While binary system is evolving, spurious oscillation occurs around 500 coordinate
time when eccentricity is about 0.17. According to result of boosted TOV star, boost parameter
might be attributed to such as oscillation and pressure perturbation is applied
to treat the problems. Because boost can spoil relativistic equilibrium, we use strong
Bernuolli’s theorem which assert homogeneous injection energy to renew equilibrium.
For highly eccentric orbit, stars collide each other before showing spurious oscillation.
Though perturbed binary delivers relived maximum density oscillation, other part is
excited at last 6, 7 percent. Relatively high constraint violation is remained problem
but it can be resolved by smoothing lapse function and metric at boundary line.
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College of Natural Sciences (자연과학대학)Dept. of Physics and Astronomy (물리·천문학부)Astronomy (천문학전공)Theses (Master's Degree_천문학전공)
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