Picture a sphere about 12 miles across that contains more mass than the Sun, bends light so severely you can see its far side, and packs billions of tons into a single teaspoon. This deep dive explores neutron stars, the densest objects in the universe short of black holes, from the iron-core collapse of a star between roughly 8 and 25 solar masses to the Tolman-Oppenheimer-Volkoff limit that keeps the remnant from collapsing further.

The hosts descend layer by layer: a millimeters-thin atmosphere, an ocean of Coulomb matter, an impossibly smooth crust where mountains stand less than a millimeter tall, the neutron drip, the lasagna, spaghetti and gnocchi phases of nuclear pasta, a frictionless neutron superfluid, and a core of quark degenerate matter. Then the exterior: pulsars spinning up to 716 times per second, Jocelyn Bell Burnell's 196 ...