An improved sink particle algorithm for SPH simulations
  Numerical simulations of star formation frequently rely on the implementation
of sink particles, (a) to avoid expending computational resource on the
detailed internal physics of individual collapsing protostars, (b) to derive
mass functions, binary statistics and clustering kinematics (and hence to make
comparisons with observation), and (c) to model radiative and mechanical
feedback; sink particles are also used in other contexts, for example to
represent accreting black holes in galactic nuclei. We present a new algorithm
for creating and evolving sink particles in SPH simulations, which appears to
represent a significant improvement over existing algorithms {\refrpt --
particularly in situations where sinks are introduced after the gas has become
optically thick to its own cooling radiation and started to heat up by
adiabatic compression}. (i) It avoids spurious creation of sinks. (ii) It
regulates the accretion of matter onto a sink so as to mitigate non-physical
perturbations in the vicinity of the sink. (iii) Sinks accrete matter, but the
associated angular momentum is transferred back to the surrounding medium. With
the new algorithm -- and modulo the need to invoke sufficient resolution to
capture the physics preceding sink formation -- the properties of sinks formed
in simulations are essentially independent of the user-defined parameters of
sink creation, or the number of SPH particles used.
