What exactly is a neutron star, you might be wondering? Well, neutron stars are the densest object known in the universe. They are created inside large stars during a supernova explosion. When the core of the star collapses, electron and proton pairs get crushed down into neutrons.
While neutron stars are only about 10-13 miles in diameter, they are heavier than many stars. A thimbleful, or sugar cube, amount of a neutron star weighs around 100 million tons. That’s more than a large mountain.