Pulsar period stability
Period extremely stable: 1 part in 10 indicates some mechanical clock mechanism - although this mechanism must be able to accommodate pulse variablity.
Pulsations of white dwarf??? (but Crab pulsar period (P~1/30 sec) too short).
Rotation of neutron star???
Notes:
Let’s consider the stability of the period of the pulsar. The period is observed to be highly stable, up to 1 part in 1e12, after allowing for the slowing down of the spin. This suggests that some ‘mechanical’ clock exists, although this mechanism must be able to accommodate the pulse-to-pulse variability of the pulse structure.
Originally, it was considered that these could be analogous to the pulsations observed in a white dwarf, as in the case of longer period variables. However, this is not a satisfactory explanation for the Crab pulsar where the period P is about 1/30 second. (We will go through the logic for this statement in the next few viewgraphs.)
The rotation of the neutron star is thus the most likely source of the pulsations.