Where Are Their Companions? Isolated Millisecond Pulsars in Globular Clusters

About 300 millisecond radio pulsars have been observed in globular clusters (GCs), motivating theoretical studies of the formation and evolution of these sources through stellar evolution coupled to stellar dynamics. Among these GC pulsars, about half are isolated, a significantly higher fraction than in the Galactic field. The fraction of isolated millisecond pulsars also tends to be higher in the more dynamically-active GCs. This is counterintuitive given the fact that millisecond pulsars are “recycled” neutron stars formed from binary mass transfer. How do these isolated millisecond pulsar form? I will show that their formation can be enhanced through neutron star tidal disruption of main-sequence stars and white dwarf collisions, which may also link to the formation of magnetars and the newly discovered fast radio bursts in a globular cluster.