Birth of millisecond pulsars in globular clusters

Abstract

The recent report that two millisecond pulsars were found in the globular cluster 47 Tuc1, together with the previous discoveries in the clusters M282, M43 and M154, indicates that formation of millisecond pulsars in globular clusters is greatly enhanced over the field, where a fourth example has recently been found5. This excess appears to be even larger than that for low-mass X-ray binaries (LMXBs), which show a factor of 100 excess (per unit mass) in globular clusters as opposed to the Galaxy6,7. If the birthrate of millisecond pulsars is indeed greater than that of LMXBs in clusters, then, contrary to the common assumption8, LMXBs cannot be the sole precursors of millisecond pulsars. Here we suggest instead that accretion-induced collapse of white dwarfs in binaries9 can form millisecond pulsars directly, without requiring a precursor LMXB stage10. Ablation of the pre-collapse binary companion by the millisecond pulsar's radiation field11, a process invoked to explain some of the characteristics of the recently discovered eclipsing millisecond pulsar5,12,13, can then yield isolated neutron stars without requiring an additional stellar encounter.