Astronomers have long relied upon particle physicists to understand the observable universe, from the Big Bang to stars such as our own Sun. In the past, the transfer of knowledge between astronomers and particle physicists has been in one direction with particle physicists providing astronomers the essential information to understand their observations. But observations of astronomical phenomena can be used to help our understanding of particle physics as well. Because of the extreme densities and temperatures which occur in neutron stars and the outbursts that make them (core-collapse supernovae), astronomers can use the objects to probe aspects of particle physics.