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. They used newer, more precise data on the nuclear reactions that create and destroy aluminum-26. It turns out the ejected amount changes by a factor of three compared to earlier calculations. It's like baking a cake from a recipe and then discovering you need three times as much flour.

The scientists also compared their results with meteorite data. They looked at ratios of aluminum-26 to other short-lived isotopes. It turned out that a single massive star cannot account for all these ratios. It seems another source is needed — for instance, another star that also exploded and polluted the cloud from which the solar system later formed.