Free Astronomy Magazine July-August 2025

19 JULY-AUGUST 2025 of during this early era of the Universe. “It is really exciting that this galaxy resembles a grand-design spiral gal- axy like our Milky Way,” says Williams. “It is gener- ally thought that it takes billions of years for this structure to form in gal- axies, but Zhúlóng shows that this could also hap- pen in only one billion years.” The rarity of galaxies like Zhúlóng suggests that spiral structures could be short-lived at this epoch of the Universe. It’s possi- ble that galactic mergers, or other evolutionary processes that are more common in the early Uni- verse, might destroy the spiral arms. Thus, spiral structures might be more stable later in cosmic time, which is why they are more common in our neighborhood. The PANORAMIC survey is novel in that it is one of the first JWST projects to use “pure parallel mode” — an efficient ob- serving strategy in which a second camera collects additional images while JWST’s main camera is pointed elsewhere. “It was definitely an ad- venture to be one of the first to use a new observing mode on a new telescope,” says Williams. Future JWST and Atacama Large Millimeter/submillimeter Array (AL- MA) observations will help confirm Zhúlóng’s properties and reveal more about its formation history. As new wide-area extragalactic surveys continue, astronomers ex- pect to find more such galaxies, of- fering fresh insights into the com- plex processes shaping the early Universe. T he image of Zhúlóng, the most distant spiral galaxy discovered to date. It has remarkably well-defined spiral arms, a central old bulge, and a large star-forming disk, resembling the structure of the Milky Way. This galaxy was discovered as part of the PANORAMIC survey — a wide-area imaging survey being conducted with the James Webb Space Telescope (JWST). The project is co-led by NSF NOIRLab assistant astronomer Christina Williams and Pascal Oesch of the University of Geneva (UNIGE). [NOIRLab/NSF/AURA/NASA/CSA/ESA/M. Xiao (University of Geneva)/G. Brammer (Niels Bohr Institute)/D. de Martin & M. Zamani (NSF NOIRLab)] NOIRLab, such as the upcoming Legacy Survey of Space and Time (LSST), which will be conducted using the NSF–DOE Vera C. Rubin Observatory. “Wide-area surveys are necessary to discover rare, massive galaxies,” says Williams, co-author on the paper presenting these results. “We were hoping to discover massive and bright galaxies across the earliest epochs of the Universe to under- stand how massive galaxies form and evolve, which helps to interpret the later epochs of their evolution that will be observed with the LSST.” Zhúlóng has a surprisingly mature structure that is unique among dis- tant galaxies, which are typically clumpy and irregular. It resembles galaxies found in the nearby Uni- verse and has a mass and size similar to those of the Milky Way. Its struc- ture shows a compact bulge in the center with old stars, surrounded by a large disk of younger stars that concentrate in spiral arms. This is a surprising discovery on sev- eral fronts. First, it shows that ma- ture galaxies that resemble those in our neighborhood can develop much earlier in the Universe than was previously thought possible. Second, it has long been theorized that spiral arms in galaxies take many billions of years to form, but this galaxy demonstrates that spiral arms can also develop on shorter timescales. There is no other galaxy like Zhúlóng that astronomers know !