Firefly Sparkle Galaxy and Companions in Galaxy Cluster MACS J1423 (NIRCam Image)

For the first time, astronomers have identified a still-forming galaxy that weighs about the same as our Milky Way if we could “wind back the clock” to weigh our galaxy as it developed. The newly identified galaxy, the Firefly Sparkle, is in the process of assembling and forming stars, and existed about 600 million years after the big bang.

The galaxy is stretched and warped due to a natural effect known as gravitational lensing, which allowed researchers to glean far more information about its contents. (In some areas of Webb’s image, the galaxy is magnified over 40 times.)

While it took shape, the galaxy gleamed with star clusters in a range of infrared colors, which are scientifically meaningful. They indicate that the stars formed at different periods, not all at once.

“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, the lead author and an assistant professor at Wellesley College in Massachusetts.

Since the galaxy is stretched into a long line in Webb’s observations, the researchers were able to identify 10 distinct star clusters and study them individually, along with the cocoon of diffuse light from the additional, unresolved stars surrounding them. That’s not always possible for distant galaxies that aren’t lensed. Instead, in many cases researchers can only draw conclusions that apply to an entire galaxy. “Most of the other galaxies Webb has shown us aren’t magnified or stretched and we are not able to see the ‘building blocks’ separately. With Firefly Sparkle, we are witnessing a galaxy being assembled brick by brick,” Mowla explained.

There are two companion galaxies “hovering” close by, which may ultimately affect how this galaxy forms and builds mass over billions of years. Firefly Sparkle is only about 6,500 light-years away from its first companion, and 42,000 light-years from its second companion. Let’s compare these stats to objects that are closer to home: The Sun is about 26,000 light-years from the center of our Milky Way galaxy, and the Milky Way is about 100,000 light-years across. Not only are these companions very close, the researchers also project that they are orbiting one another.

Each time one galaxy interacts with another, gas compresses, allowing new stars to form in clumps. “It has long been predicted that galaxies in the early universe form through successive interactions and mergers with other, tinier galaxies,” explained Yoshihisa Asada, a co-author and doctoral student at Kyoto University in Japan. “We might be witnessing this process in action.”

This 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 clusters, the light emitted by stars outside the clusters, and identify two companion galaxies, which enhanced the team’s research.

Mowla picked out the Firefly Sparkle galaxy while closely examining Webb’s CAnadian NIRISS Unbiased Cluster Survey (CANUCS), which includes near-infrared images from NIRCam (Near-Infrared Camera) and spectra from the microshutter array aboard NIRSpec (Near-Infrared Spectrograph). She was drawn to its gleaming star clusters, because sparkly objects typically indicate things that are extremely clumpy and complicated. Since the galaxy looks like a “sparkle” or swarm of lightning bugs on a warm summer night, the team nicknamed it the Firefly Sparkle galaxy.