Astronomers estimate that it takes about 7 billion years (about half the age of the universe) to create a galaxy like ours. So you can imagine their surprise when they observed ceers-2112, a galaxy with the same shape as the Milky Way, well ordered and quite massive, only 2 billion years after the Big Bang.
Our galaxy, the Milky Way, is known as a barred spiral galaxy. It has several arms containing several billion stars and a central sausage-shaped block of overdensity from which the arms extend in a spiral manner. Other spirals have a more spherical core, like the Whirlpool galaxy.
The general idea is that galaxies start out as a chaotic mess. Thanks to gases falling on them from intergalactic space and collisions with other galaxies, they grow and eventually settle into disks or spheres. The disk is where the spiral arms are found and at the heart of the disk the oldest stars are found in bulge or bar formations. It was thought that barred spiral galaxies like the Milky Way could not be seen until the universe was at least half its current age (13.8 billion years), but it appears that the process is much faster than expected.
“This galaxy, named ceers-2112, formed shortly after the Big Bang,” co-author Dr Alexander de la Vega of the University of California explained in a statement. “The discovery of ceers-2112 shows that galaxies in the early universe could be as ordered as the Milky Way. This is surprising because galaxies were much more chaotic in the early universe and very few had structures similar to those of the Milky Way.
“The bar in ceers-2112 suggests that galaxies matured and became ordered much more quickly than we previously thought, meaning that some aspects of our theories about galaxy formation and evolution need to be revised.”
Ceers-2112 suggests that galaxies may not take billions of years to become orderly, well-behaved spiral galaxies. For this galaxy, the bar could have assembled in just 400 million years and the disk of stars could have been happily in place more than 12 billion years ago. Ceers-2112 is the closest ancestor of the Milky Way discovered during the first 4 billion years of the universe and its discovery will change both theories and observations, which in this case were carried out by JWST .
“First, theoretical models of galaxy formation and evolution will need to take into account that some galaxies became stable enough to host bars very early in the history of the universe. These models may need to adjust the amount of dark matter that makes up galaxies in the early universe, because dark matter is thought to affect the rate at which bars form,” de la Vega said.
“Second, the discovery of ceers-2112 demonstrates that structures such as bars can be detected when the universe was very young. This is important because galaxies in the past were smaller than they are today, making finding bars more difficult. The discovery of ceers-2112 paves the way for the discovery of other bars in the young universe.
The study is published in Nature.