Lecture 30 - Millisecond Pulsars

If one tries to describe the development of our understanding of ``Millisecond Pulsars'', it would look very much like the work report of the Astrophysics Group of Raman Research Institute in the 1980s-'90s. The group was headed by Prof. G. Srinivasan at that time, and it was he (alongwith Prof. V. Radhakrishnan) took the main initiative in this activity. In fact, great strides were made from this group in the overall area of the evolution of Neutron Stars during this period.

A neutron star spinning 642 times a second was discovered in 1982! Although it was a `solitary pulsar', a bold conjecture was made that it must be a ``recycled pulsar" - like the Hulse-Taylor pulsar - spun up in a low-mass binary, which somehow `got rid' of its binary companion. This scenario led to the prediction that its magnetic field must be more than 10,000 times weaker than that of the Crab pulsar. Later observations confirmed this prediction. Forty years later, nearly 150 such "Millisecond Pulsars" have been discovered, all with very nearly the same magnetic field. Millisecond Pulsars are remarkable objects for several reasons. As "clocks", they are more stable than even "atomic clocks" which define the `standard of time'. They spin fast enough for the next generation of terrestrial detectors to detect gravitational waves emitted by them. Plans are also underway to use an "array" of such pulsars as a `detector' of low-frequency gravitational waves.