Neutron stars form from collapsed supernova cores. Their matter is so densely packed that atoms are crushed into neutrons. A single cubic centimeter weighs about 400 million tons.
The gravity on a neutron star is so strong that a falling object would hit the surface at one-third the speed of light. This matter is incomprehensibly dense — essentially atomic nuclei mashed together. Scientists study neutron stars to explore quantum mechanics and the behavior of matter at extreme densities. They’re cosmic laboratories revealing the universe’s most intense pressures and the limits of known physics.