About J2021+4026
J2021+4026 is an uncommon pulsar. It spins once every 265.318 ms and carries a surface magnetic field around 3.85×10^12 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.