PSR J1748-2446ad

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PSR J1748-2446ad is currently (as of July 2015) the fastest rotating known millisecond pulsar . Its extremely precisely determined rotation frequency is 716.35556 Hertz ( standard deviation 0.00003), corresponding to a rotation time of less than 1.4 milliseconds. It replaces the record holder PSR B1937 + 21 with 642 Hertz (1.6 milliseconds rotation time) that was found in 1982 .

The pulsar was discovered on November 10, 2004 by Jason WT Hessels ( McGill University ) at the 100-meter radio telescope in Green Bank in the globular cluster Terzan 5 and confirmed on January 8, 2005. Its radius must be less than 16 kilometers, its rotational speed at the equator is around 24 percent of the speed of light . A lower limit for the duration of rotation is the centrifugal force, which must be smaller than the gravity on the surface. For a neutron star 20 kilometers in diameter, the lower limit of the period of rotation is in the range of 1 millisecond per revolution.

PSR J1748-2446ad forms with a main sequence star of presumably 0.14 solar masses, from which the pulsar subtracts mass, a binary star system , which is located in the globular star cluster Terzan 5 in the constellation Sagittarius and is therefore an estimated 19,000 light years away from Earth. The pulsar and the main sequence star orbit each other every 26 hours in an almost circular orbit, but the pulsar is not visible for about 40 percent of its orbit because it is covered by the gas curtain of its companion.

The period of rotation of the pulsar only slows down by less than 3 · 10 −13 Hertz / second. This could be explained by the emission of electromagnetic waves . A possible indication of the radiation of gravitational waves has not yet been found.