About J1312+1810D
J1312+1810D is a rare pulsar. It spins once every 6.07 ms and has a dispersion measure of 24.6 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.