About J1021-5601
J1021-5601 is an uncommon pulsar. It spins once every 670.026 ms, has a dispersion measure of 212 pc cm⁻³ and carries a surface magnetic field around 1.91×10^11 G.
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.