Spin-down of rapidly rotating neutron stars

Exact compressible and incompressible sequences of Maclaurin spheroids are used to model the evolution of rapidly rotating pulsars by accretion, electromagnetic radiation, and gravitational radiation. The hoop conjecture of Thorne (1972) is used to explore the formation of black holes by loss of rotational support during pulsar spindowns. It is found that a rapidly rotating pulsar's changing oblateness has observable consequences in measurements of its P and braking index. For very stiff equations of state, this suppresses P somewhat a high rotation rates, but for softer equations of state P can actually be negative, corresponding to spinup, even as the pulsar is losing angular momentum. A rapidly rotating pulsar born with an 0.5 ms period and the Crab pulsar are used to illustrate the usefulness of these exact models. 27 refs