Neutron stars are the collapsed cores of supergiant stars. They are created as a result of supernovas and gravitational collapse, and are the second-smallest and densest class of stellar objects. In the cores of these stars, protons and electrons combine to form neutrons. Neutron stars can be classified as pulsars if they are magnetized, if they rotate, and if they emit beams of electromagnetic radiation out of their magnetic poles. They may include soft gamma repeaters (SGR) and radio-quiet neutron stars, as well as pulsars such as radio pulsars, recycled pulsars, low mass X-ray pulsars, and accretion-powered pulsars. A notable grouping of neutron stars includes the Magnificent Seven.