Identify the phases in the life cycle of small and big stars. supernova: in this stage, the star collapses and produces elements heavier than iron. planetary nebula: in this stage, the star emits strong energy pulses that push away the outer layers creating a cloud of ionized gas around the core. neutron star: in this stage, the star has reduced to an extremely dense core. white dwarf: in this stage, the star has reduced to a dense core.