Emilio Tejeda, Stephan Rosswog
A generalized Newtonian potential is derived from the geodesic motion of test particles in Schwarzschild spacetime. This potential reproduces several relativistic features with higher accuracy than other commonly used pseudo-Newtonian approaches. The new potential reproduces the exact location of the marginally stable, marginally bound, and photon circular orbits, as well as the exact radial dependence of the binding energy and the angular momentum of these orbits. Moreover, it reproduces the orbital and epicyclic angular frequencies to better than 6%. In addition, the spatial projection of general trajectories coincide with their relativistic counterparts, while the time evolution of parabolic-like trajectories and the pericentre advance of elliptical-like trajectories are both reproduced exactly. We apply this approach to a standard thin accretion disc and find that the efficiency of energy extraction agrees within 3% with the exact relativistic value, while the energy flux per unit area as a function of radius is reproduced everywhere to better than 7%. As a further astrophysical application we implement the new approach into a smoothed particle hydrodynamics code and study the tidal disruption of a main sequence star by a supermassive black hole. The obtained results are in very good agreement with previous relativistic simulations of tidal disruptions in Schwarzschild spacetime. The equations of motion derived from this potential can be easily implemented into existing Newtonian hydrodynamics codes at virtually zero additional computational effort.
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http://arxiv.org/abs/1303.4068
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