JWST reveals that galaxies grow up quickly in our Universe

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.

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.

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.

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.

Perhaps the most famous dust-obscured galaxy is the Black Eye galaxy, known as either Messier 64 or NGC 4826. This semi-dark appearance is due to a thick layer of central dust in the disk of the spiral galaxy, which blocks starlight maximally where it is tipped toward us, at about the 3 o’clock position, and is least dusty in the opposite (9 o’clock) position due to being tipped away from us in that direction.

The Southern Pinwheel Galaxy, Messier 83, displays many features common to our Milky Way, including a multi-armed spiral structure and a central bar, as well as spurs and minor arms, plus a central bulge of stars. The pink regions showcase transitions in hydrogen atoms driven by ultraviolet light: produced by new stars. The Southern Pinwheel galaxy is one of the closest and brightest barred spiral galaxies at a distance of just 15 million light-years, and has a similar diameter (118,000 light-years) to our own Milky Way.

This optical view of barred spiral galaxy NGC 1365 showcases a variety of features: star formation, a central supermassive black hole, extended spiral arms, a massive central bar, and dust-rich features that block the light from stars behind them. Our Milky Way is a barred spiral, although less severely so, making NGC 1365 an object of particular relevance to understanding our home galaxy.

Shown along with contoured lines that indicate lensing magnification within the cluster, the Firefly Sparkle galaxy is shown in a central box with two nearby companion galaxies also highlighted. Within the arc, ten individual bright spots corresponding to star clusters of 100,000+ solar masses apiece appear: similar to how our Milky Way might have appeared at a similarly early time in cosmic history.

This selection of 55 galaxies from the JWST’s GLASS Early Release Science program spans a variety of ranges in redshift and mass. This helps teach us what shapes galaxies take on over a range of masses and stages in cosmic time/evolution, revealing a number of very massive, very early, yet very evolved-looking galaxies. If we can see them now, they’ll always be visible, a contrast to the myth of the disappearing Universe.

The distant galaxy J0107a is shown as imaged by JWST’s NIRCam instrument at a wavelength of 3.56 microns, on the left, and from a specific carbon monoxide transition occuring in its gas by ALMA, on the right. The data from both observatories, combined, indicates not only a rotating disk with spiral features, but the presence of a large, extended central bar: the earliest one ever discovered.

The blown-up galaxy shown here, serendipitously captured as JWST observed the field of the quasar shown at right, is the largest disk galaxy ever observed within the first 2 billion years of cosmic history. Located at a redshift of z=3.25, when the Universe was 1.95 billion years old, it spans 100,000 light-years across and contains more than six times the stellar mass of the modern Milky Way galaxy.

Although local, irregular motions are found within various features inside the Big Wheel galaxy, overall it is observed to rotate at similar speeds to the stars in the Milky Way: orbiting the center at ~200 km/s. The bulk, overall rotation is consistent with the presence of large quantities of dark matter.

This image shows a deep galaxy field containing a great many nearby, intermediate, and ultra-distant galaxies, along with an inset image with ALMA data that shows the morphology of the disk-like galaxy REBELS-25, as seen just ~700 million years after the Big Bang.

This animation shows the transition between ESO VISTA data (orange) and ALMA data (blue, white, and red), where the latter shows the velocity profile of what VISTA clearly shows is a disk galaxy. This makes REBELS-25, the galaxy imaged here, the earliest, youngest rotating disk galaxy ever discovered: just 700 million years after the Big Bang.

Within the vast and impressive JADES field of view, galaxy JADES-GS-z7-01-QU contains only 400-600 million solar masses worth of stars has been spotted, whose light arrives just 700 million years after the Big Bang. While the stars inside this galaxy span perhaps ~3000 light-years across, star-formation proceeded in a giant burst that ended 10-20 million years prior to our observations. It is unknown whether this is a “pause” or a permanent cessation to its star-formation.

The distant galaxy MACS1149-JD1 is gravitationally lensed by a foreground cluster, allowing it to be imaged at high resolution and with multiple instruments, including Hubble and ALMA. Based on measurements of the stellar populations found inside, this object, whose light comes from when the Universe was just 530 million years old, contains stars that are at least 280 million years old within it. It shows strong evidence of differential motions inside of it, suggesting rotation, but it does not have an identifiable disk.

Hubble data (background) and ALMA data (inset, false-colored) revealed the internal motions, for the first time, of normal galaxies whose light was less than 1 billion years old. The color in the blown-up ALMA images shows the relative motions (red is away, blue is towards) internal to these two galaxies, displaying a rotating, whirlpool-like pattern similar to what’s exhibited within the modern Milky Way.