Accretion by a Neutron Star Moving at a High Kick Velocity in the Supernova Ejecta

Abstract

We suggest a two-dimensional time dependent analytic model to describe the ac- cretion of matter onto a neutron star moving at a high speed across the ejecta left in the aftermath of a supernova explosion. The formation of a strange star resulting from the ac- cretion is also addressed. The newborn neutron star is assumed to move outward at a kick velocity of vns ∼ 10 3 km s −1 , and the accretion flow is treated as a dust flow. When the neutron star travels across the ejecta with high speed, it sweeps up material, and when the accreted mass has reached a critical value, the neutron star will undergo a phase transition, for instance, to become a strange star. Our results show that the accretion rate decreases in a complicated way in time, not just a power law dependence: it drops much faster than the power law derived by Colpi et al. We also found that the total accreted mass and the phase transition of the neutron star depend sensitively on the velocity of supernova ejecta.