Free Astronomy Magazine March-April 2025

MARCH-APRIL 2025 T his trio of galaxies exists in the galaxy cluster MACS J1423, which was observed by the Hubble Space Telescope in its Cluster Lensing And Supernova survey with Hubble (CLASH) program. Hubble was the first to image this galaxy, now known as the Firefly Sparkle. Webb was able to resolve seven additional star clus- ters, the light emitted by stars outside the clusters, and identify two companion galaxies, which enhanced the team’s research. [NASA, ESA, CSA, STScI, Chris Willott (NRC-Canada), Lamiya Mowla (Wellesley College), Kartheik Iyer (Columbia)] surrounded by diffuse light from other unresolved stars,” said Iyer. “This galaxy is literally in the process of assembling.” Webb’s data show the Firefly Sparkle galaxy is on the smaller side, falling into the category of a low-mass gal- axy. Billions of years will pass before it builds its full heft and a distinct shape. “Most of the other galaxies Webb has shown us aren’t magnified or stretched, and we are not able to see their ‘building blocks’ separately. With Firefly Sparkle, we are witness- ing a galaxy being assembled brick by brick,” Mowla said. Since the galaxy is warped into a long arc, the researchers easily picked out 10 distinct star clusters, which are emitting the bulk of the galaxy’s light. They are represented here in shades of pink, pur- ple, and blue. Those colors in Webb’s images and its sup- porting spectra confirmed that star formation didn’t happen all at once in this galaxy, but was staggered in time. “This galaxy has a diverse population of star clusters, and it is remarkable that we can see them separately at such an early age of the uni- verse,” said Chris Willott from the National Research Coun- cil of Canada’s Herzberg As- tronomy and Astrophysics Re- but there are two galaxies that the team confirmed are “hanging out” within a tight perimeter and may in- fluence how it builds mass over bil- lions of years. Firefly Sparkle is only 6,500 light- years away from its first companion, and its second companion is sepa- rated by 42,000 light-years. For con- text, the fully formed Milky Way is about 100,000 light-years across — all three would fit inside it. Not only are its companions very close, the re- searchers also think that they are orbiting one another. Each time one galaxy passes another, gas condenses and cools, allowing new stars to form in clumps, adding to the galaxies’ masses. “It has long been predicted that galaxies in the early universe form through successive in- teractions and mergers with other tinier galaxies,” said Yoshihisa Asada, a co-author and doctoral student at Ky- oto University in Japan. “We might be witnessing this process in action.” T his illustration depicts a re- construction of what the Firefly Sparkle galaxy looked like about 600 million years after the big bang if it wasn’t stretched and dis- torted by a natu- ral effect known as gravitational lensing. This con- cept is based on images and data from NASA’s James Webb Space Tele- scope. [NASA, ESA, CSA, Ralf Crawford (STScI)] search Centre, a co-author and the observation program’s principal in- vestigator. “Each clump of stars is un- dergoing a different phase of for- mation or evolution.” The galaxy’s projected shape shows that its stars haven’t settled into a central bulge or a thin, flattened disk, another piece of evidence that the galaxy is still forming. Researchers can’t predict how this disorganized galaxy will build up and take shape over billions of years, !