About J0103+54
J0103+54 is an uncommon pulsar. It spins once every 354.304 ms and has a dispersion measure of 55.6 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.