sentences:  In addition, from carbon-burning onwards, energy loss via neutrino production becomes significant, leading to a higher rate of reaction than would otherwise take place.This continues until nickel-56 is produced, which decays radioactively into cobalt-56 and then iron-56 over the course of a few months.As iron and nickel have the highest binding energy per nucleon of all the elements, energy cannot be produced at the core by fusion, and a nickel-iron core grows.