Although all three kinds of objects are neutron stars, the things that they can be seen to do and the physics that causes this are very different. But there are some things that are similar. For example, X-ray pulsars are probably old rotation-powered pulsars that have already lost most of their energy, and can only be seen again after their binary companions expanded and matter from them started falling onto the neutron star. The process of accretion (matter falling onto the neutron star) can in turn give enough angular momentum energy to the neutron star to change it into a rotation-powered :millisecond pulsar.