Radioactive Decay and Light Curve
The light from the explosion reaches a maximum, then
slowly fades. The fading is due to the radioactive decay of cobalt and nickel to iron.
This is the source of the iron in the Earth’s core and elsewhere.
Since the object that explodes is
always a white dwarf at the Chandrasekhar limit, these “Type I” supernovae make a
“standard
bomb” that can be used to judge very great distances (using the
inverse square law).