Evolutionary Trajectories of Ultracompact “Black Widow” Pulsars With Very Low Mass Companions

The existence of millisecond pulsars with planet-mass companions in close orbits is challenging from the stellar evolution point of view.We calculate in detail the evolution of binary systems self-consistently, including mass transfer, evaporation, and irradiation of the donor by X-ray feedback, demonstrating the existence of a new evolutionary path leading to short periods and compact donors as required by the observations of PSR J1719-1438.We also point out the alternative of an exotic nature of the companion planet-mass star.