Stellar archaeology and black widow pulsars

Abstract

Many forms of dark matter might collect in or near stars. Although it may have little observable effect on the star itself, one way to find such dark matter would be to eliminate the rest of the star. The recent discovery¹ of PSR1957 + 20 suggests the existence of 'black widow' neutron stars, which destroy their companion by ablation, and supports previous conjectures² that isolated millisecond pulsars were spun up by companions that were later disposed of. Any exotic, non-degradable residuum would remain in orbit around the pulsar. In this letter we note that a statistically viable sample of millisecond pulsars may present a means of looking for excavated exotic matter at the cores of previously existing stars. The mass threshold of detectability using pulsar timing, 3 x 10⁻⁸ M_⊙ or less (J. Taylor, personal communication), would provide a much stronger constraint than previous considerations³ and is of astrophysical interest.