About once every century, a massive star somewhere in our galaxy runs out of fuel.
This happens after millions of years of heat and pressure have fused the star's hydrogen into heavier elements like helium, carbon, and nitrogen— all the way to iron.
No longer able to produce sufficient energy to maintain its structure, it collapses under its own gravitational pressure and explodes in a supernova.
The star shoots most of its innards into space, seeding the galaxy with heavy elements.
But what this cataclysmic eruption leaves behind might be even more remarkable: a ball of matter so dense that atomic electrons collapse from their quantum orbits into the depths of atomic nuclei.
The death of that star is the birth of a neutron star: one of the densest known objects in the universe, and a laboratory for the strange physics of supercondensed matter.
But what is a neutron star?
Think of a compact ball inside of which protons and electrons fuse into neutrons and form a frictionless liquid called a superfluid— surrounded by a crust.
This material is incredibly dense – the equivalent of the mass of a fully-loaded container ship squeezed into a human hair, or the mass of Mount Everest in a space of a sugar cube.
Deeper in the crust, the neutron superfluid forms different phases that physicists call "nuclear pasta,"as it's squeezed from lasagna to spaghetti-like shapes.
