Birth accelerations of neutron stars

Abstract

We suggest that neutron stars experienced at birth three related physical changes, which may originate in magneto-rotational instabilities: (i) an increase in period from the initial value P₀ to the current value P_s, implying a change of rotational energy Δ E_rot; (ii) an exponential decay of its magnetic field from the initial value B₀ to the current surface value B_s, implying a change of radiative energy Δ E_rad; and (iii) an increase of space velocity from the initial value v₀ to the current value v, implying a change of kinetic energy Δ E_kin. These changes are assumed to be connected by Δ E_rad + Δ E_kin = Δ E_rot. This means that the radiation loss and increase of kinetic energy are both at the expense of a rotational energy loss. It is shown that this energy conversion occurs during times of order of 10⁻⁴ s if the neutron stars are born with magnetic fields in the range of 10¹⁵–10¹⁶ G and initial periods in range 1–20 ms. It is shown that the birth accelerations of neutron stars are of the order of 10⁸g.