Why Neutron Stars Are the Universe's Densest Computers

A neutron star packs about 1.4 solar masses into a sphere just 20 kilometers across — so dense that a sugar-cube-sized chunk weighs as much as a mountain. It's held up by neutron degeneracy pressure — quantum mechanical resistance to further compression, the same force that stabilizes white dwarfs. Some rotate hundreds of times per second, beaming radio waves like cosmic lighthouses; we call these pulsars. Their pulses are so regular that we use them as natural clocks to test Einstein's relativity and detect gravitational waves. A single teaspoon of neutron star material would weigh roughly 6 billion tons.