About J2238+6021
J2238+6021 is an uncommon pulsar. It spins once every 3,070 ms and has a dispersion measure of 185.3 pc cm⁻³.
The collapsed core of a star that exploded: about one and a half Suns of matter crushed into a ball the size of a city, held up only by the refusal of neutrons to be squeezed further.