Such large velocities are perhaps not surprising, given the
violent conditions which form neutron stars. Shklovskii [142] 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.
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Binary and Millisecond Pulsars
D. R. Lorimer (dunc@mpifr-bonn.mpg.de) http://www.livingreviews.org/lrr-1998-10 © Max-Planck-Gesellschaft. ISSN 1433-8351 Problems/Comments to livrev@aei-potsdam.mpg.de |