About J1731-3123
J1731-3123 is an uncommon pulsar. It spins once every 753.048 ms, has a dispersion measure of 354.5 pc cm⁻³ and carries a surface magnetic field around 1.14×10^12 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.