Neutron Stars Are Incredibly Dense

Imagine an object the size of a city that contains more mass than our entire Sun. This is the reality of a neutron star, the remnant of a massive star's explosive death in a supernova. When such a star exhausts its fuel, gravity wins the final battle. The star's core collapses with such unimaginable force that it crushes protons and electrons together, forming a super-dense ball composed almost entirely of neutrons. This process packs the mass of a sun into a sphere only about 20 kilometers, or 12 miles, across.

The resulting material is so extraordinarily compact that its properties defy everyday intuition. A single sugar-cube-sized amount would have a mass comparable to Mount Everest. This bizarre state of matter was first theorized in the 1930s by Walter Baade and Fritz Zwicky, but it remained a wild concept for decades. It wasn't until 1967 that astronomer Jocelyn Bell Burnell detected the first one. She observed a source emitting radio waves with clockwork regularity and discovered the first "pulsar," which was quickly identified as a rapidly spinning neutron star—a cosmic lighthouse confirming the existence of these incredible objects.