PSR J0437−4715

PSR J0437−4715 is a pulsar. Discovered in the Parkes 70 cm survey, it remains the closest and brightest millisecond pulsar (MSP) known. The pulsar rotates about its axis 173.7 times per second and therefore completes a rotation every 5.75 milliseconds. It emits a searchlight-like radio beam that sweeps past the Earth each time it rotates. Currently the most precisely located object outside of the Solar System, PSR J0437-4715 is 156.3 parsecs or 509.8 light-years distant.

This pulsar is distinguished by being the most stable natural clock known and is debatably more stable than man-made atomic clocks. Its stability is about one part in 1015. Two other pulsars, PSR B1855+09 and PSR B1937+21 are known to be comparable in stability to atomic clocks, or about 3 parts in 1014.

PSR J0437−4715 is the first MSP to have its X-ray emission detected and studied in detail. It is also the first of only two pulsars to have the full three-dimensional orientation of its orbit determined.

Optical observations indicate that the binary companion of PSR J0437-4715 is most likely a low-mass helium white dwarf. The pulsar is about 1.4 solar mass and the companion is about 0.25. The pair revolve around each other every 5.75 days in nearly perfect circular orbits.