The Secret Life of Black Widow Companions

Black Widows are rapidly spinning magnetized neutron stars with companions that are only a few percent the mass of the Sun. I will present numerical stellar evolution tracks showing how main sequence stars are reduced to such low masses by magnetic braking and Roche-lobe overflow. The numerical results are explained by an analytical model, similar to the Hayashi track, but accounting for the pulsar’s gamma-ray irradiation. I will compare the theory to radio and gamma-ray observations of the pulsars, as well as to novel optical images of the companions themselves. I will demonstrate that the mass at which a Black Widow companion becomes fully convective is a simple function of its orbital period, allowing us to study stellar structure and magnetism away from the main sequence in a controlled manner.