For the first time, astronomers have identified a still-forming galaxy that weighs about the same as our Milky Way would have when it was in its infancy. This newly discovered galaxy, nicknamed the Firefly Sparkle, is in the process of assembling and forming stars, existing just 600 million years after the Big Bang.
The galaxy’s stretched and warped appearance is the result of gravitational lensing, a natural effect that magnifies distant objects. This phenomenon allowed researchers to gather unprecedented details about the galaxy’s structure, with some parts of the galaxy appearing over 40 times larger.
The Firefly Sparkle galaxy shines brightly with star clusters in a range of infrared colors, which indicate that the stars are forming at different stages, rather than all at once. This provides a rare glimpse into the evolutionary stages of a galaxy as it forms.
“I didn’t think it would be possible to resolve a galaxy that existed so early in the universe into so many distinct components, let alone discover a Milky Way-mass galaxy in the process of forming,” said Lamiya Mowla, lead author of the study and an assistant professor at Wellesley College in Massachusetts.
The researchers were able to identify 10 distinct star clusters in the galaxy. The galaxy itself is elongated due to gravitational lensing, which allowed for detailed study of its structure. Unlike other distant galaxies where stars appear as a single mass, the Firefly Sparkle allows astronomers to see the "building blocks" of a galaxy forming, star by star.
Adding to the complexity, two companion galaxies are located nearby—just 6,500 and 42,000 light-years away from the Firefly Sparkle. These galaxies may play a significant role in shaping the galaxy’s development over billions of years. The close proximity of these companions suggests they may eventually merge, with interactions that could trigger new star formations.
“This discovery is significant because it supports the long-standing theory that galaxies in the early universe formed through successive interactions and mergers with smaller galaxies,” explained Yoshihisa Asada, a co-author of the study and a doctoral student at Kyoto University.
The Firefly Sparkle exists in the galaxy cluster MACS J1423, which was previously studied by the Hubble Space Telescope as part of the Cluster Lensing And Supernova Survey with Hubble (CLASH) program. While Hubble was the first to image the galaxy, the James Webb Space Telescope provided new insights, resolving additional star clusters and detecting the two companion galaxies.
Mowla and her team discovered the Firefly Sparkle while analyzing Webb’s Canadian NIRISS Unbiased Cluster Survey (CANUCS), which includes infrared images and spectra from Webb's NIRCam and NIRSpec instruments. The team was drawn to the galaxy's sparkling star clusters, leading them to nickname it the Firefly Sparkle, resembling a swarm of glowing fireflies in the dark.
This discovery offers a remarkable opportunity to study the early stages of galaxy formation, providing valuable insight into how galaxies like the Milky Way may have formed in the distant past.
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