Astronomers have witnessed evidence of an extremely violent collision between planets, and it resembles the event in Earth's history that created the moon.
Neutron stars are the remnants of supernova explosions. They're known for their extreme density, and it's often said and written that a teaspoon of neutron star weighs as much as the combined weight of all of Earth's approximately 8 billion human beings. The only thing denser than a neutron star is a black hole.

