Free Astronomy Magazine January-February 2023

21 JANUARY-FEBRUARY 2023 team was struck by being able to measure the shapes of these first galaxies; their calm, orderly disks question our understanding of how the first galaxies formed in the crowded, chaotic early universe.” This remarkable discovery of com- pact disks at such early times was only possible because of Webb’s much sharper images, in infrared light, compared to Hubble. “These galaxies are very different than the Milky Way or other big galaxies we see around us today,” said Treu. Illingworth emphasized the two bright galaxies found by these teams have a lot of light. He said one option is that they could have been very massive, with lots of low- mass stars, like later galaxies. Alter- natively, they could be much less massive, consisting of far fewer ex- traordinarily bright stars, known as Population III stars. Long theorized, they would be the first stars ever born, blazing at blistering tempera- tures and made up only of primor- dial hydrogen and helium – before stars could later cook up heavier el- ements in their nuclear fusion fur- naces. No such extremely hot, pri- mordial stars are seen in the local universe. “Indeed, the farthest source is very compact, and its colors seem to indicate that its stellar pop- ulation is particularly devoid of heavy elements and could even con- tain some Population III stars. Only Webb spectra will tell,” said Adriano Fontana, second author of the Castellano et al. paper and a mem- ber of the GLASS-JWST team. Present Webb distance estimates to these two galaxies are based on measuring their infrared colors. Eventually, follow-up spectroscopy measurements showing how light has been stretched in the expanding universe will provide independent verification of these cosmic yardstick measurements. NASA, ESA, CSA, Tommaso Treu (UCLA) − Zolt G. Levay (STScI) the University of Geneva in Switzer- land, second author of the Naidu et al. paper. The Webb observations nudge as- tronomers toward a consensus that an unusual number of galaxies in the early universe were so much brighter than expected. This will make it easier for Webb to find even more early galaxies in subsequent deep sky surveys, say researchers. “We’ve nailed something that is in- credibly fascinating. These galaxies would have had to have started coming together maybe just 100 mil- lion years after the big bang. No- body expected that the dark ages would have ended so early,” said Garth Illingworth of the University of California at Santa Cruz, a mem- ber of the Naidu/Oesch team. “The primal universe would have been just one hundredth its current age. It’s a sliver of time in the 13.8 billion- year-old evolving cosmos.” Erica Nelson of the University of Col- orado in Boulder, a member of the Naidu/Oesch team, noted that “our GLASS galaxy, referred to as GLASS- z12, which is believed to date back to 350 million years after big bang. The previous record holder is galaxy GN-z11, which existed 400 million years after the big bang (redshift 11.1), and was identified in 2016 by Hubble and Keck Observatory in deep-sky programs. “Based on all the predictions, we thought we had to search a much bigger volume of space to find such galaxies,” said Castellano. “These observations just make your head explode. This is a whole new chapter in astronomy. It’s like an ar- chaeological dig, and suddenly you find a lost city or something you didn’t know about. It’s just stag- gering,” added Paola Santini, fourth author of the Castellano et al. GLASS-JWST paper. “While the distances of these early sources still need to be confirmed with spectroscopy, their extreme brightnesses are a real puzzle, chal- lenging our understanding of galaxy formation,” noted Pascal Oesch at !