An ultraluminous nascent millisecond pulsar

Abstract

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 105 yr. The observed (isotropic) luminosity of 1040 erg s−1 also supports the notion that the neutron star will spin up to a millisecond period upon accreting about 0.1 Mȯ – the reported hard X-ray luminosity of this ULX, together with the spin-up value, implies torques consistent with the accretion disc extending down to the vicinity of the stellar surface, as expected for low values of the stellar dipole magnetic field (B ≲ 109 G). This suggests a new channel of millisecond pulsar formation – in high-mass X-ray binaries – and may have implications for studies of gravitational waves, and possibly for the formation of low-mass black holes through accretion-induced collapse.