If we could travel far beyond our galaxy and look at the Milky Way, it would be an amazing sight. Bright spirals extend from the central core, with dust and nebulae scattered around the edges of the spiral. When you think of a galaxy, you probably think of a spiral galaxy like the Milky Way, but spirals make up only 60% of the galaxies we see. This is because spiral galaxies form only when smaller galaxies collide and merge over time. At least that’s what we thought, as a new study published on the preprint server. arXivshows that this is not the case.

The standard model of galaxies is that they evolve over time. Galaxies formed from huge clouds of primordial hydrogen and helium and probably initially had a very amorphous structure. Given the density of the early universe, galaxy collisions and mergers were common, causing galaxies to spin and the formation of disks and spirals. All of this takes time, so we expect spiral galaxies to be fairly common in the local Universe, but rare in the early Universe.

This new study used data from the Cosmic Evolution Early Release Science Survey (CEERS) collected by the James Webb Space Telescope. The team identified 873 galaxies with masses greater than 10 billion solar masses and redshifts between z = 0.5 and z = 4. Galaxies at this redshift are between 5 and 12 billion years old, so they cover the range from early galaxies to modern galaxies.

216 of these galaxies were classified as spirals. The authors noted that some galaxies might have been misassembled, but even then the 108 galaxies were unanimously classified as spirals by the raters. When the team sorted them by redshift, they found that the proportion of spirals decreased as we went back in time, while at redshifts above z = 3, the proportion of spirals was much higher than expected. When the team calibrated the observations, they found that about one-fifth of the galaxies at z = 3 were spiral galaxies. These very early galaxies should have spiraled less than two billion years after the Big Bang; This meant that there would be little time for mergers and collisions to occur.

In other words, many galaxies formed into a disk-shaped spiral quite early in the universe. Therefore, although collisions and mergers play a role in the formation of spiral galaxies, other factors are likely to come into play as well. It is not yet known what these factors are. With future JWST data, the team hopes to determine how these early galaxies evolved and why spiral galaxies have persisted for so long.