Millisecond pulsar

This is consistent with the spin-up hypothesis of their formation, as the extremely high stellar density of these clusters implies a much higher likelihood of a pulsar having (or capturing) a giant companion star.

[12] In early 2007 data from the Rossi X-ray Timing Explorer and INTEGRAL spacecraft discovered a neutron star XTE J1739-285 rotating at 1122 Hz.

[16] Gravitational waves are an important prediction from Einstein's general theory of relativity and result from the bulk motion of matter, fluctuations during the early universe and the dynamics of space-time itself.

They act as highly accurate clocks with a wealth of physical applications ranging from celestial mechanics, neutron star seismology, tests of strong-field gravity and Galactic astronomy.

The idea is to treat the solar system barycenter and a distant pulsar as opposite ends of an imaginary arm in space.

The pulsar acts as the reference clock at one end of the arm sending out regular signals which are monitored by an observer on the Earth.

The effect of a passing gravitational wave would be to perturb the local space-time metric and cause a change in the observed rotational frequency of the pulsar.

Each further limited the gravitational wave background and, in the second case, techniques to precisely determine the barycenter of the solar system were refined.

[25][26] In June 2023, NANOGrav published the 15-year data release, which contained the first evidence for a stochastic gravitational wave background.