(CNN) For the first time ever, scientists have observed the spectacular collision of two neutron stars. A NASA animation recreates what happened. Neutron stars are amazingly dense and very small. They have masses bigger than our sun, compressed into a body with a diameter roughly the size of a city like Chicago. In an event captured by earth-based telescopes in August — two neutron stars entered a death spiral and collided. The collision released more energy than has been released during our sun’s entire lifetime. It also emitted electromagnetic waves and space-time ripples. It even scattered heavy elements like gold and platinum across the universe.