"The answer can be found at the center of stars. As mentioned earlier in the story, hydrogen fusion occurs inside stars. When tremendous pressure is applied to multiple atoms, they combine to form a new atom. When this happens, a large amount of energy is generated. that is the true source of all the star's heat. Hydrogen is the simplest type of atom, and forcing them together results in the second simplest type, helium. Hydrogen becomes helium through nuclear fusion, and helium eventually becomes the main driver of more reaction. Further fusion of these atoms produces carbon and oxygen. Stars with a mass less than 10 times that of our sun cannot generate enough pressure to fuse carbon or oxygen. These stars lose their heat over time, eventually becoming [White Dwarf] stars. Stars with more than 10 times the mass of the sun produce iron with the nuclear fusion reactions occurring at their centers. Iron, being a highly stable element, prevents further fusion reaction from occurring. Nuclear fusion reactions may have stopped, but the enormous weight of the star compresses upon itself, eventually causing a supernova explosion. A star with a mass 10 to 20 times that of the Sun will have a nucleus that remains after such a supernova explosion. These are neutron stars. If the mass of these becomes even greater, they will become a black hole. Now, what happens when these cycles continue over and over for hundreds of billions of years? The answer is [Iron]. Celestial debris scattered by a supernova explosion will eventually be captured by the gravity of neighboring stars. Generally, it is understood that most of the matter will gravitate towards the black hole at the center of a galaxy. However, neutron stars will eventually cool down, and black hole will evaporate. What will be left then? Iron. Iron will be left. Extremely dense iron under extremely high pressure. Yes, heavy metal. Heavy...metal...... H.e.a.v.y....m.e.t.a.l... At the end of the universe, heavy metal is all that will remain." --Lanmoliwf, the last Angel.