About J2219+4754
J2219+4754 is an uncommon pulsar. It spins once every 538.469 ms, has a dispersion measure of 43.5 pc cm⁻³ and carries a surface magnetic field around 1.23×10^12 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.