Lorenzo Roberti

Aluminum-26 is an isotope that doesn't live long by cosmic standards: only about a million years. When a massive star explodes as a supernova, it flings this aluminum into space. Later, it decays, emitting gamma rays that telescopes can catch. The authors recalculated how much aluminum-26 a star with 20 solar masses should eject.

The Murchison meteorite, which fell in Australia in 1969, holds dust grains older than the Solar System. Among them are tiny graphite grains smaller than a thousandth of a millimeter. In five such grains, researchers found the isotope strontium-84: its atoms are slightly lighter than ordinary strontium.

Deep inside a massive star, before it explodes, layers sit on top of each other like the layers of an onion. Sometimes two adjacent layers, the carbon and oxygen layers, mix together. It's like how layers of broth and vegetables in a pot of soup blend when you stir them with a spoon.