An ultraluminous nascent millisecond pulsar

Abstract

If the ultraluminous source (ULX) M82 X-2 sustains its measured spin-up value of $\dot \nu= 10^{-10}\,{\rm s^{-2}}$, it will become a millisecond pulsar in less than $10^5\,$ years. The observed (isotropic) luminosity of $10^{40}\,$ erg/s also supports the notion that the neutron star will spin up to a millisecond period upon accreting about $0.1\,{\rm M_\odot}$---the reported hard X-ray luminosity of this ULX, together with the spin-up value, implies torques consistent with the accretion disk extending down to the vicinity of the stellar surface, as expected for low values of the stellar dipole magnetic field ($B\lesssim 10^9\,$G). This suggests a new channel of millisecond pulsar formation---in high-mass X-ray binaries (HMXBs)---and may have implications for studies of gravitational waves, and possibly for the formation of low-mass black holes through accretion-induced collapse.