Transcript: The iron at the center of a massive evolved star is not the familiar metal that we are used to, even though the density is very high. The temperature is also high, a billion Kelvin or more, so the iron is a high temperature gas or plasma. Iron is the most stable element, so energy is consumed to make elements more massive than iron. Thus, the heart of a massive star is an iron tomb. There are, however, two ways in which elements heavier than iron can be produced. Helium capture does not work, but neutron capture does. And so in a process called the S process, S for slow, neutrons can gradually be added to heavy element nuclei to build elements in the periodic table all the way up to bismuth. The second way is when the energy is derived from the core collapse of a dying star, a supernova. In this rapid process enough energy is deposited in an explosion to create heavy elements up to radium, uranium, and plutonium by what’s called the R process, R for rapid.