A Millisecond Pulsar Progenitor to an Ultra-Compact Low-Mass X-ray Binary

Abstract

We discuss a twist in binary neutron star evolution scenarios in which a millisecond pulsar system is actually a progenitor for a low-mass X-ray binary system. After 7 billion years of orbital decay due to gravitational radiation, the millisecond pulsar PSR J0751+1807 will enter a low-mass X-ray binary phase. When the orbital period reaches about 5 minutes, the white dwarf will overflow its Roche lobe, transferring mass to the neutron star. Its predicted observational X-ray parameters are very similar to the ultra-compact low-mass X-ray binary 1820–303. The ultimate fate of the system after Roche-lobe overflow is unknown. One possibility is that the companion may eventually tidally disrupt, leaving a disk of material which could form into planets.