What were the first galaxies in the Universe like? Current observations can only access a handful of these ancients. However, a new simulation has synthesized millions to better understand the galaxies of 13 billion years ago.
Galaxy Zoo is a citizen science project that uses volunteers to classify galaxies from the Sloan Digitial Sky Survey as spiral or elliptical. Now the Galaxy Zoo 2 catalogue has gone public, with even more detailed classifications of galaxies, including bars, bulges, spiral arms, and round and squashed ellipticals.
The central question of this Letter is how and when the Milky Way assembled its stellar mass. This issue is addressed by tracing the formation history of spiral galaxies which closely resemble the Milky Way.