Lost and found dark matter in elliptical galaxies

An elliptical argument Over four fifths of the mass in the Universe is ‘dark matter’: it can't be seen directly but we know it's there because the motions of stars show that they are gravitationally attracted by something unseen. Elliptical galaxies, formed by the merger of spiral and disk-shaped galaxies, ought in this picture to contain just as much dark matter as any other galaxies. So the recent suggestion that they contained no dark matter — because the paths of slow-moving stars in ellipticals seemed not to be subject to dark matter's gravitational tug — was a blow to the conventional view of the Universe. Now Dekel et al. present computer simulations of the mergers that produce ellipticals, and they find that these processes can generate stars in slow elongated orbits even when the merged galaxies contain the usual complement of dark matter.