For 10 points, almost all heavier-than-iron metals in the universe originate in what extremely-energetic stellar events?
Cas A was produced by one of these events, and has been dated using light echoes. One process in them causes reactions that occur along the neutron drip line; that process is called "rapid" or "r". Perimutter et al received the 2011 Nobel Prize for the use of these events in distant galaxies as standard candles to show that the universe is expanding. In 1054 AD, one of them produced the Crab Nebula. One type of them, referred to as "one-A", can occur after a white dwarf accretes to a mass greater than 1.4 solar masses, known as the Chandrasekhar limit. For 10 points, almost all heavier-than-iron metals in the universe originate in what extremely-energetic stellar events?
Cas A was produced by one of these events, and has been dated using light echoes.
supernovae [do not prompt on or accept "nova"]