Binary stars create long-lasting supernovae by expelling material before explosion

Binary stars are the sole source of interacting supernovae, which remain luminous for years. New research indicates that mass transfer between stars in a binary system creates a dense cocoon of material. This cocoon fuels the extended brightness when the massive star explodes. This phenomenon, known as Case C mass transfer, is thought to account for about 13% of core-collapse supernovae and aligns with observations of specific events like SN 2014C.