About J1954+1021
J1954+1021 is an uncommon pulsar. It spins once every 2,099.44 ms, has a dispersion measure of 80.87 pc cm⁻³ and carries a surface magnetic field around 1.93×10^12 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.