Astronomers have discovered the oldest spiral galaxy - a twin of the Milky Way

The James Webb Infrared Space Telescope has discovered the oldest spiral galaxy with a junction to date. It is very similar to our Milky Way, but originated when the Universe was two billion years old. This means that this type of galaxy appeared much earlier than scientists thought.

About two-thirds of all spiral galaxies (that's nearly 60 percent of all galaxies in the universe) known to astronomers, including the Milky Way, have a junction at their center - a huge elongated structure filled with young stars. The spiral arms in such galaxies are strongly twisted and begin at the ends of the lintel, whereas in a normal spiral galaxy these arms emerge from the center of the galactic nucleus.

Models of galaxy formation and evolution show that structures with (as well as without) a jumper did not begin to appear until about four billion years after the Big Bang. Scientists believe that in the early Universe, Milky Way analogs, if any, are extremely rare because they are too "fragile" and would not have survived mergers with other similar objects. At the beginning of time, such "cosmic accidents" were quite common.

A group of scientists from the Spanish Astrobiology Center under the leadership of Luca Costantini found in the data set of the space telescope "James Webb" the oldest to date the galaxy with a jumper. The researchers noted that this galaxy was already mature when the age of the universe was two billion years and it strongly resembles the Milky Way. The scientists worked with Cosmic Evolution Early Release Science (CEERS) images of thousands of very distant galaxies, which the James Webb received in June 2022.

The new object has been named ceers-2112. Its stellar mass is 3.9 × 10⁹ solar masses. Simulations showed that the galaxy should have grown to the size of the Milky Way four billion years after the Big Bang, and the first cold stellar disk in ceers-2112 could have formed more than 12 billion years ago.

"If it were possible to go back in time, we would see that it is very likely that the Milky Way would look like ceers-2112," Costantini explained.

The authors concluded that further observations of such objects could help scientists improve models of galaxy formation and understand how the Milky Way and other similar structures with a lintel evolved in the early universe.

Note that a little earlier in the Astrophysical Journal published a paper by other scientists from the University of Manchester (UK) and the University of Victoria (Canada), in which astronomers described the type of galaxies dominant in the early Universe. In their study, the team used the same dataset (CEERS) as their Spanish colleagues.

The experts found that as early as one or two billion years after the Big Bang, the Universe became dominated by disk galaxies - aka spiral galaxies (both with and without a junction). Before that, it was thought that irregular and pecular galaxies were common in the early Universe. The latter have pronounced individual features, because of which it is impossible to assign them to a particular class.

Astronomers have studied 3956 galaxies that observed "James Webb". First, each of the objects scientists analyzed on the basis of its appearance, and then attributed to one of the six categories. In the final version, the researchers' galaxy classification table looked as follows:

1. Disk galaxies - 1672 (or about 42 percent);

2. Spheroidal galaxies - 553 (or nearly 14 percent);

3. Pecular galaxies - 1100 (or about 27 percent);

4. Uncertain sources - 428 (or about 10 percent);

5. Intense sources - 55 (or about one percent);

6. Galaxies whose type could not be determined - 148 (or nearly four percent).

The scientists then examined the galaxies based on their morphological features. To do this, they used the Morfometryka program: it allowed them to evaluate each object based on information about asymmetry, smoothness, entropy, spirality, and size. The resulting data helped the researchers understand how a particular galaxy evolved from the first billion years of the universe.

The researchers summarized that in the early Universe the most common are disk galaxies: they occur 10 times more often than many experts previously assumed, based on Hubble observations.

In itself, the formation of a spiral galaxy two billion years after the Big Bang is not particularly surprising, but such features of "maturity", such as a pronounced lintel and cold stellar disks, do look strange. Until now, these were thought to be the product of many billions of years of galactic evolution and therefore not found in such an early Universe.