The largest galaxies displayed here aren’t blurry because they’re overexposed or because of atmospheric interference, but rather because JWST is outstandingly exposing their diffuse, extended stellar halos. Behind the central and lower-right galaxies are more distant, gravitationally lensed background galaxies, many of which show quite evolved features. (Credit: ESA/Webb, NASA & CSA, G. Gozaliasl, A. Koekemoer, M. Franco, and the COSMOS-Web team)
The first galaxies were irregular blobs of gas and stars. But modern features, like spiral arms and bars, appeared earlier than expected.
Galaxies are vitally important cosmic structures.
This region of space, of approximately the same size and area as the previous sparse region, instead shows a large group of foreground galaxies with a rich population of background galaxies located behind them. The bright central spike-rich galaxy likely contains an active supermassive black hole at its center. (Credit: ESA/Webb, NASA & CSA, G. Gozaliasl, A. Koekemoer, M. Franco, and the COSMOS-Web team)
Nearly all of the Universe’s stars, planets, and opportunities for life exist within them.
Galaxies comparable to the present-day Milky Way are numerous, but younger galaxies that are Milky Way-like are inherently smaller, bluer, and richer in gas in general than the galaxies we see today. Fewer galaxies have disks and spiral shapes as we look farther back in time. Over time, many smaller galaxies become gravitationally bound together, resulting in mergers, but also in groups and clusters containing large numbers of galaxies overall. (Credit: NASA, ESA, P. van Dokkum (Yale U.), S. Patel (Leiden U.), and the 3-D-HST Team)
Modern ones display huge varieties in size, mass, morphology, and evolutionary features.
This nearby galaxy, NGC 1277, although it may appear similar to other typical galaxies found in the Universe, is remarkable for being composed primarily of older stars. Both its intrinsic stellar population and its globular clusters are all very red in color, indicating that it hasn’t formed new stars in ~10 billion years. When all of the gas within a galaxy is expelled and no new gas enters, that galaxy becomes permanently “red and dead,” as no new populations of stars can form within it. (Credit: NASA, ESA, and M. Beasley (Instituto de Astrofísica de Canarias))
Elliptical galaxies are often “red and dead,” gas-free and devoid of star-formation.
Galaxy clusters, like Abell S740, are the largest bound structures in the Universe. When spirals merge, for example, a large number of new stars form, but either post-merger or by speeding through the intra-cluster medium, gas can be stripped away, leading to the end of star formation in that galaxy and, eventually, a red-and-dead final structure. It is possible that red-and-dead galaxies can form much earlier in the Universe’s history than current observations indicate, with JWST offering hints that this is the case. (Credit: NASA, ESA, Hubble Heritage Team (STScI / AURA); J. Blakeslee)
