The sun is of only average mass, starwise, and after burning through the last of its hydrogen fuel in about five billion years, its outer layers will drift away, and the core will eventually compact to become what's known as a white dwarf, an Earth-size ember of the cosmos.
For a star ten times as big as the sun, death is far more dramatic. The outer layers are blasted into space in a supernova explosion that, for a couple of weeks, is one of the brightest objects in the universe. The core, meanwhile, is squeezed by gravity into a neutron star, a spinning ball bearing a dozen miles in diameter. A sugar-cube-size fragment of a neutron star would weigh a billion tons on Earth; a neutron star's gravitational pull is so severe that if you were to drop a marshmallow on it, the impact would generate as much energy as an atom bomb.
But this is nothing compared with the death throes of a star some 20 times the mass of the sun. Detonate a Hiroshima-like bomb every millisecond for the entire life of the universe, and you would still fall short of the energy released in the final moments of a giant-star collapse. The star's core plunges inward. Temperatures reach 100 billion degrees. The crushing force of gravity is unstoppable. Hunks of iron bigger than Mount Everest are compacted almost instantly into grains of sand. Atoms are shattered into electrons, protons, neutrons. Those minute pieces are pulped into quarks and leptons and gluons. And so on, tinier and tinier, denser and denser, until. ..
Until no one knows. When trying to explain such a momentous phenomenon, the two major theories governing the workings of the universe – general relativity and quantum mechanics – both go haywire, like dials on an airplane wildly rotating during a tailspin.
The star has become a black hole. (Michael Finkel, National Geographic)