Up to half of the matter in our Milky Way galaxy may come from distant galaxies, astrophysicists have discovered in a first-of-its-kind analysis. As a result, each one of us may be made in part from extragalactic matter. Using supercomputer simulations, the researchers found an unexpected mode for how galaxies acquired matter: intergalactic transfer. Supernova explosions eject copious amounts of gas from galaxies, causing atoms to be transported from one galaxy to another via powerful galactic winds.