Young Galaxies Grow Up Fast

Astronomers have captured the most detailed look yet at faraway galaxies at the peak of their youth, an active time when the adolescent galaxies were fervently producing new stars. The observations focused on 18 galaxies located 12.5 billion light-years away. They were imaged across a range of wavelengths from ultraviolet to radio over the past eight years by a trio of telescopes: NASA's Hubble Space Telescope; NASA's James Webb Space Telescope (JWST); and ALMA (Atacama Large Millimeter/submillimeter Array) in Chile, of which the U.S. National Science Foundation National Radio Astronomy Observatory is a partner. Data from other ground-based telescopes were also used to make measurements, such as the total mass of stars in the galaxies.

"With this sample, we are uniquely poised to study galaxy evolution during a key epoch in the universe that has been hard to image until now," says Andreas Faisst, a staff scientist at IPAC, a science and data center for astronomy at Caltech. "Thanks to these exceptional telescopes, we have spatially resolved these galaxies and can observe the stages of star formation as they were happening and their chemical properties when our universe was less than a billion years old."

Faisst, who led the observations, which were conducted as part of the ALPINE-CRISTAL-JWST Survey, presented the results at the 247^th meeting of the American Astronomical Society on January 6, 2026, in Phoenix. The results were published in The Astrophysical Journal Supplement. The survey program consists of an international team of more than 50 scientists across more than 15 institutions.

A key finding from the survey is that the galaxies are maturing faster in several ways than researchers previously believed. For one, the galaxies are more chemically enriched than expected, which means they have produced more heavy elements, in particular carbon and oxygen, than was thought possible during this early age of the cosmos.

As galaxies evolve, pockets of gas within them condense and ignite into stars. The new stars churn out heavy elements like carbon, which then become building blocks for the next generation of stars. Ultimately, these heavy elements (referred to as metals in astronomy) are required to make planetary systems, and even humans, in the case of our own solar system.

"How do metals form in less than 1 billion years? It was a surprise to see such chemically mature galaxies," Faisst says. "It's like seeing 2-year-old children act like teenagers."

And these teenagers are hungry. The data also show that the supermassive black holes within almost half of these galaxies are actively accreting material, or "feeding," implying that the black holes are rapidly growing.

In a similar vein, previous results from a parent ALPINE survey found that many of these young galaxies exhibit rotating disks—a sign that the galaxies' physical structures (similar in appearance to our own spiral Milky Way) had developed earlier than predicted. (The parent survey contained 118 galaxies, of which the 18 in the new study are a subset.)

"Now, with this new survey, we can show that some of these galaxies were both structurally and chemically evolved," Faisst says.

In addition to the galaxies themselves, the new study found that their surrounding gas—the so-called circumgalactic medium—was also chemically enriched. "The galaxies show very flat gradients in their metal abundances, reaching out to more than 30,000 light-years," notes co-author Wuji Wang, a postdoc at IPAC working with Faisst.

The ALPINE-CRISTAL-JWST survey is the first to both spatially resolve galaxies as far away as 12.5 billion light-years and to image them at multiple wavelengths. The spatially resolved images allow the astronomers to point to regions of gas, dust, and metals within the galaxies and begin to deduce exactly how stars were being manufactured and how the galaxies were being chemically enriched to eventually become similar to our Milky Way, with planetary systems like our own. The multiwavelength coverage is important because each component of a galaxy (stars, gas, dust) emits light at different wavelengths, and observing all these components simultaneously allows researchers to understand a galaxy as a whole.

In the future, the team plans to study the growth and metal enrichment of these galaxies in more detail using cosmological simulations, including those created by Phil Hopkins, Caltech's Ira S. Bowen Professor of Theoretical Astrophysics. "The combination of observations and simulations provides a powerful synergy to understand the details of star formation, and dust and metal production mechanisms," Faisst says. "The knowledge of these will ultimately help us understand the formation of the first stars and planets and how our own Milky Way came into being."

The study titled "The ALPINE-CRISTAL-JWST Survey: JWST/IFU Optical Observations for 18 Main-Sequence Galaxies at z=4-6" was funded by NASA. Other Caltech authors include postdoc Yu-Heng Lin, Caltech Optical Observatory astronomer Lin Yan (PhD '96), and graduate student Lunjun (Simon) Liu (MS '25). A companion paper, led by Seiji Fujimoto of the University of Toronto, was submitted to The Astrophysical Journal.