Tidal Disruption of a Star By a Massive Black Hole Computed In Fermi Normal Coordinates Public Deposited

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  • March 22, 2019
  • Cheng, Roseanne Marie
    • Affiliation: College of Arts and Sciences, Department of Physics and Astronomy
  • We present a new numerical code constructed to obtain accurate simulations of encounters be tween a star and a massive black hole. We assume Newtonian hydrodynamics and self-gravity for the star. The three-dimensional parallel code includes a PPMLR hydrodynamics module to treat the gas dynamics and a Fourier transform-based method to calculate the self-gravity. The formalism for calculating the relativistic tidal interaction in Fermi normal coordinates (FNC) allows the addition of an arbitrary number of terms in the tidal expansion. We present the relevant post-Newtonian terms for this code. Results are given for an n = 1.5 polytrope with comparisons between simulations and predictions from the linear theory of tidal encounters. It is shown that the inclusion of the l = 3 tidal term will cause the center of mass of the star to deviate from the origin of the FNC. We consider relativistic encounters for three different mass ratios, µ = 1.28×10−3,4.21×10−4,3.77×10−5. We show a relativistic suppression in the amount of energy deposited onto the star. We find that the dimensionless function T2(η) (which characterizes the energy deposited into non-radial oscillations) must not only be a function of the dimensionless disruption parameter, η, but also of a dimensionless relativistic parameter Φp. We speculate on the source of the observed energy excess in the tidal en counter simulations from the linear theory. We find that the energy deposited into radial oscillations is negligible and that the shock heating in the outer layers of the post-encounter star contributes a significant amount. We estimate the new orbital parameters of the star after it passes by the black hole.
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  • In Copyright
  • Evans, Charles
  • Doctor of Philosophy
Graduation year
  • 2012

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