Stellar evolution
A much bigger red giant leaves behind a black hole. A black hole is created because gravity is so strong that even the protons and neutrons collapse in on themselves. Even light can no longer escape a black hole. Since there is nothing we know of stronger than the force that holds atomic nuclei (the plural of 'nucleus') together, some physicists think that a black hole collapses all the way down to a mathematical point called a singularity.