<human>:  Where do pulsars come from?
<bot>: Pulsars are the rapidly spinning cores of collapsed stars. They are incredibly dense, and have a mass about 1.4 times that of the Sun. They are also incredibly small, with a diameter of about 10 km. They are so dense that they are thought to be made of neutrons, and they emit a beam of radiation that is thought to be caused by the rotation of the neutron star.