What happens inside neutron stars, the universe's densest known objects?

A typical neutron star has a mass a few times the mass of the sun, compressed into a region only a dozen kilometers across.

Neutron stars' surface gravities are so intense that the largest "mountains" are only a few millimeters tall.

In the cores of neutron stars, the crushing pressures can squeeze apart atomic nuclei and maybe even protons and neutrons themselves.

In other models, all protons and neutrons break down completely, forming a soup of quarks and gluons, the carriers of the strong nuclear force.

The nearest neutron star is hundreds of light-years away, and even if we could crack it open, the special conditions that create these kinds of exotic conditions would break down.

The only way to peer inside neutron stars is with math and a heavy dose of guesswork.