# Neutron star spin-up

Neutron star spin up is the name given to the increase in rotational speed over time first noted in Cen X-3 and Her X-1 but now observed in other X-ray pulsars. In the case of Cen X-3, the pulse period is decreasing over a timescale of 3.4·103 years (defined as ${\displaystyle P/{\dot {P}}}$, where ${\displaystyle P}$ is the rotation period and ${\displaystyle {\dot {P}}}$ is the rate of change in the rotation period).