Disk galaxies may be hiding ancient spherical galaxies

New Scientist : In 2005 astronomers discovered that compact spherical galaxies were abundant in the early universe. However, that type of galaxy is not present in nearly the same concentration in the local universe, which is instead dominated by elliptical galaxies. One explanation was that, over time, those early spherical galaxies were destroyed by colliding with other galaxies. But there is not enough evidence of such collisions to clinch the case. Now, Alister Graham of Swinburne University of Technology in Melbourne, Australia, and his colleagues propose a different explanation: Many of the elliptical galaxies in the local universe are actually disk galaxies, and their apparent thickness is an optical illusion. Graham’s team found 21 galaxies that they say are disks with a central bulge that matches the characteristics of the old compact spherical galaxies. They suggest that instead of major collisions, these galaxies formed through minor mergers that didn’t destroy the structure of the spherical galaxies. If so, there could be up to 1000 times as many of the ancient galaxies still present as previously thought.