Millisecond Pulsars

A millisecond pulsar (MSP) is a rapidly rotating neutron star with a spin period of the order of milliseconds. MSPs are thought to be recycled old pulsars that have been spun up by the accretion of matter from a companion star. They are the most stable astronomical clocks known, and are used for precise timing measurements.

MSPs were first discovered in 1982. The first MSP, PSR B1937+21, had a spin period of 1.558 ms. As of 2017, there are over 250 known MSPs. MSPs have been found in binary systems as well as in globular clusters. The Binary Radio Pulsar Explorer (BRPEX) is a dedicated survey mission to search for radio pulsars in binary systems using the Parkes radio telescope in Australia.

The fastest-known spinning MSP is PSR J1748-2446ad, with a spin rate of 716 Hz or 43,000 rpm. This object was discovered in 2006 using the Green Bank Telescope in West Virginia, USA. PSR J1748-2446ad lies within the Terzan 5 globular cluster and has an orbital period of just 2 hours around its white dwarf companion star.

PSR B1937+21 was the first millisecond pulsar to be found, with a spin rate of 642 Hz or 39,120 rpm – about 60 times faster than an electric motor! This object was discovered by Russell Hulse and Joseph Taylor while they were searching for evidence of gravitational waves using ground-based radio telescopes at Princeton University in New Jersey, USA. PSR B1937+21 is also notable because it was used to confirm Einstein’s theory of general relativity through observations of its orbit around another neutron star companion.(1)

Since their discovery, millisecond pulsars have provided some of the most precise tests of general relativity and other theories beyond Einstein’s theory.(2)(3)(4) For example,PSR J0437-4715 has been used to test whether spacetime curvature near Earth deviates from that predicted by general relativity.(5) Observationsof double neutron star binaries such as PSRs B1913+16and B1534+12 can be usedto study how these objects evolve over time due to emissionof gravitational waves – one consequenceof Einstein’s theoryof general relativity.(6)(7) Finally, millisecondpulsars can also be usedas powerful toolsfor detecting and characterizingexoplanets.(8) For instance, radial velocity measurementsmade using data fromPSR B1257+12 ledto the discoveryof three planets orbiting this MSP– making itthe first extrasolar planetary systemto be foundaround a pulsar.(9)

Millisecondpulsars offera unique windowinto many aspects astrophyiscalprocesses – fromthe evolutionof double neutronstarsto testingtheoriesbeyond Einsteinto probingthe natureand distributionexoplanetarysystems.<10>