2.2 Pulse periods and slowdown rates
The present public-domain catalogue , available on-line , contains up-to-date parameters for
over 1500 pulsars. Most of these are “normal” with pulse periods which increase secularly at
rates . A growing fraction are “millisecond pulsars”, with and
. For many years, the most rapidly rotating neutron star known was the original millisecond
pulsar B1937+21 , with . However, one of the recent discoveries in the globular cluster
Terzan 5 appears to be rotating even more rapidly, with . Confirmation of this exciting
result should be published in due course. While the hunt for “sub-millisecond pulsars” continues, and
most neutron star equations of state allow shorter periods, it has been suggested [36, 60] that
the lack of pulsars with is caused by gravitational wave emission from R-mode
As can be seen from the “ diagram” in Figure 3, normal and millisecond pulsars are distinct
populations. The differences in and imply fundamentally different magnetic field strengths and
ages. Treating the pulsar as a rotating magnetic dipole, one may show  that the surface magnetic field
strength and the characteristic age .
Lines of constant and are drawn on Figure 3, from which we infer typical values of
and for the normal pulsars and and for the millisecond pulsars. For the rate of
loss of kinetic energy, sometimes called the spin-down luminosity, we have . The lines of
constant shown on Figure 3 show that the most energetic objects are the very young normal pulsars
and the most rapidly spinning millisecond pulsars.
||The diagram showing the current sample of radio pulsars. Binary pulsars are
highlighted by open circles. Theoretical models  do not predict radio emission outside the dark
blue region. Figure provided by Michael Kramer.