Vignyana Patashala

The first Millisecond pulsar was discovered in 1982. Today, more than a hundred are known. Their origin and evolution are considered ‘well understood’. Nevertheless, millisecond pulsars (ms-PSR) are, once again, under the spotlight for several reasons. (i)  The Fermi Telescope has discovered a large number of gamma ray emitting millisecond pulsars. (ii) An ‘array’ of millisecond pulsars have been monitored by radio astronomers for several decades now with the objective of detecting ultra-low frequency gravitational waves from merging supermassive black holes. Recently, there have been claims of success. (iii) There is optimism that the upgraded LIGO should be able to detect gravitational waves from millisecond pulsars.

Within days of the discovery of the first ms-PSR, astronomers at RRI argued that, although solitary, it must have been born and ‘recycled’ in low-mass X-ray binary. The concept of ‘reincarnation’ of dead pulsars was first advanced at the RRI forty five years ago. Various aspects of the recycling scenario were elucidated and elaborated on in a series of prescient papers published from the RRI during the 1980s.

In these two lectures, I propose to revisit, and explain in detail, various aspects of the recycling scenario. I believe that the three points mentioned in the first paragraph of this Abstract, as well as the occasion of the Platinum Jubilee of the institute, justify this walk down memory lane. In order to resurrect a dead pulsar as a millisecond pulsar, two things must happen. (i) The magnetic field of the neutron star must decay by many orders of magnitude, and (ii) It must be spun-up to an ultra-short period. My objective in these two lectures would be to explain the underlying physics. Both the lectures will be pedagogical and no prior knowledge of astronomy would be assumed.