A millisecond pulsar progenitor to an ultracompact low-mass X-ray binary

With a pulsar timing baseline of 10 years, the orbital period decay due to gravitational radiation will be measurable for the recently discovered short orbital period millisecond pulsar PSR J0751+1807. This is the first white dwarf-neutron star binary system with an orbit compact enough for such a measurement to be possible. The cooling age of the white dwarf in this system will be impossible to measure due to the possible effect of heating by the pulsar emission. After 7 billion years of orbital decay, when the orbital period reaches about 5 minutes, PSR J0751+1807 will enter an ultracompact low-mass X-ray binary phase. Its predicted observational X-ray parameters are very similar to the ultracompact 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 that could form into planets.