Most stars in the universe today are found in massive galaxies called ellipticals, named for their stretched-out-circle shape. Unlike our own galaxy, which is a spiral with arms extending out from the centre, the edges of elliptical galaxies are smooth. At first glance, these galaxies might seem like simple systems. However, they are among the most mysterious objects in the cosmos. Elliptical galaxies host extremely old stars and are not forming new stars. Exactly how these dead galaxies form is a question both observational and theoretical astronomers have tried to answer for a long time. Our new study, published in Nature Astronomy, could help solve this puzzle.