Smoothed particle hydrodynamics with radiation transfer

Abstract

A method for adding radiation transfer to smoothed particle hydrodynamics is described. One dynamic time-step of an SPH calculation is run in the normal way but with an additional time- step constraint that the change in the internal energy of any particle is limited to the greater of 10 per cent of its initial value or the equivalent of a 2 K temperature increase. The internal energy of the SPH particles is then transferred to the elements of a tree structure ('leafs') that become the radiating elements. The radiation is simulated by streams of superphotons, called 'phots' that are followed through the system until either they are absorbed by another leaf or they leave the system. When the radiation transfer is complete the internal energy of the leafs is transferred back to the SPH particles ready for the next dynamical step. The method has been validated by comparison with theoretical results in a number of situations. The method is particularly useful where the modelled system contains subsystems with a variety of opacity regimes that may also change with time.