Such large velocities are perhaps not surprising, given the violent conditions which form neutron stars. Shklovskii  demonstrated that, if the explosion is only slightly asymmetric, an impulsive ``kick'' velocity of up to 1000 km s is imparted to the neutron star. As a result, a newly formed high-velocity pulsar quickly leaves its birth site close to the Galactic plane and on average it migrates to higher Galactic latitudes. This effect is seen most dramatically in Fig. 7, a dynamical simulation of the orbits of 100 neutron stars in a model of the Galactic gravitational potential.
Using the proper motion data, recent studies have demonstrated that the mean birth velocity of normal pulsars is 450 km s ([105, 96, 48, 64]; see, however, also [71, 69]). This is significantly larger than the millisecond pulsars -- recent studies suggest that their mean birth velocity is likely in the range km s [93, 47, 107]. The main reason for this difference surely lies in the fact that about 80% of the millisecond pulsars are members of binary systems (§ 2.4) which couldn't have survived if the neutron star had received a substantial kick velocities.
|Binary and Millisecond Pulsars
D. R. Lorimer (firstname.lastname@example.org)
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