Radiation from the pulsar PSR B1509-58, a rapidly spinning neutron star, makes nearby gas glow in X-rays (gold, from Chandra) and illuminates the rest of the nebula, here seen in infrared (blue and red, from WISE)

A model that shows what a neutron star would look like on the inside section.

A neutron star is a very small and dense star made almost completely of neutrons. They are small stars with a radius of about 11–11.5 kilometres. They have a mass of about twice that of the Sun. They are the smallest and densest stars known to exist in the Universe. They are what is left of a huge star which exploded as a supernova.