About J1958+56
J1958+56 is an uncommon pulsar. It spins once every 311.8 ms and has a dispersion measure of 58.1 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.