A millisecond pulsar (MSP) is a pulsar with a rotational period in the range of about 1–10 milliseconds. Millisecond pulsars have been detected in the radio, X-ray, and gamma ray portions of the electromagnetic spectrum. The leading theory for the origin of millisecond pulsars is that they are old, rapidly rotating neutron stars which have been spun up or "recycled" through accretion of matter from a companion star in a close binary system. For this reason, millisecond pulsars are sometimes called recycled pulsars.