Isentropic 'shock waves' in numerical simulations of astrophysical bodies

TL;DR

This paper investigates the differences between standard shock wave solutions and isentropic shock waves in astrophysical simulations, highlighting the potential errors when assuming entropy conservation in high-amplitude shock scenarios.

Contribution

It demonstrates that using isentropic equations in high-energy astrophysical shocks can lead to significant inaccuracies, emphasizing the importance of energy conservation in such simulations.

Findings

Numerical errors increase when assuming entropy conservation in strong shocks.

Isentropic equations are only suitable for weak or non-disruptive shocks.

Standard shock solutions better represent high-energy astrophysical phenomena.

Abstract

Strong discontinuities in solutions of the gas dynamic equations under isentropic conditions, i.e., with continuity of entropy at the discontinuity, are examined. Solutions for a standard shock wave with continuity of energy at the discontinuity are compared with those for an isentropic 'shock wave'. It is shown that numerical simulation of astrophysical problems in which high-amplitude shock waves are encountered (supernova explosions, modelling of jets) with conservation of entropy, rather than of energy, leads to large errors in the shock calculations. The isentropic equations of gas dynamics can be used only when there are no strong discontinuities in the solution or when the intensity of the shocks is not high and they do not significantly affect the flow.