Firefly Sparkle: Webb telescope 'weighs' a galaxy for the first time

For the first time, the James Webb Space Telescope (JWST) has unveiled and measured a galaxy from the early universe — one with a mass akin to what the Milky Way might have had during its formative years.

Nicknamed the Firefly Sparkle, this galaxy existed just 600 million years after the Big Bang and gleams with 10 distinct star clusters, providing an unprecedented glimpse into galactic assembly. 

Unlike other galaxies from this epoch, which are typically much larger, Firefly Sparkle is a relatively lightweight galaxy.

Firefly Sparkle: A galaxy like no other

“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 find that its mass is similar to that of our own galaxy when it was in the process of forming,” said Lamiya Mowla, co-lead author and assistant professor at Wellesley College.

“There is so much going on inside this tiny galaxy, including so many different phases of star formation.”

This extraordinary discovery was made possible by the combined effects of nature and technology.

A massive foreground galaxy cluster amplified the distant galaxy’s appearance through gravitational lensing, and the James Webb Space Telescope’s (JWST) state-of-the-art infrared imaging delivered unparalleled clarity.

“Without the benefit of this gravitational lens, we would not be able to see this galaxy in such detail,” explained Kartheik Iyer, co-lead author and NASA Hubble Fellow at Columbia University. “We knew to expect it based on current physics, but it’s surprising that we actually saw it.”

The galaxy, named for its sparkling clusters reminiscent of fireflies on a summer night, immediately captivated Mowla due to its unique characteristics.

Reconstructing the shape of Firefly Sparkle 

To understand the true structure of the Firefly Sparkle galaxy, the research team reconstructed its shape, removing the distortions caused by gravitational lensing.

They discovered it resembles an elongated raindrop containing clusters of stars at various stages of development.

“Our reconstruction shows that clumps of actively forming stars are surrounded by diffuse light from other unresolved stars,” Iyer said. “This galaxy is literally in the process of assembling.”

Despite its small size, Firefly Sparkle falls into the category of low-mass galaxies. It will take billions of years for it to evolve into a larger, more distinct form. 

“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 witnessing a galaxy being assembled brick by brick,” Mowla added.

The building blocks of a galaxy

Thanks to the gravitational lensing effect, the galaxy appears as a stretched arc, allowing researchers to identify 10 star clusters contributing most of its light. 

These clusters, glowing in shades of pink, purple, and blue, provide critical evidence that star formation in Firefly Sparkle occurred in staggered phases rather than all at once.

“This galaxy has a diverse collection of star clusters, and it is remarkable that we can see them separately at such an early age of the Universe,” said co-author Chris Willott, a scientist at the National Research Council Canada. “Each clump of stars is at a different stage of formation or evolution.”

The galaxy’s elongated and disorganized shape further suggests its stars have not yet coalesced into a central bulge or thin disc, suggesting that Firefly Sparkle is still in its formative phase.

Neighboring galaxies and future growth

Firefly Sparkle is not alone. Two companion galaxies orbit nearby and are likely to influence its growth and shape over billions of years. 

The nearest companion lies just 6,500 light-years away, while the second is separated by 42,000 light-years – both distances relatively small compared to the Milky Way’s 100,000-light-year diameter. 

Researchers believe these companions are close enough to interact gravitationally, driving gas condensation and new star formation during each orbital pass.

“It has long been predicted that galaxies in the early Universe form through successive interactions and mergers with other tinier galaxies,” said study co-author Yoshihisa Asada, a doctoral student at Kyoto University. “We might be witnessing this process in action.”

New horizons in galactic discovery

Firefly Sparkle is just one of many galaxies that will be uncovered by the Webb telescope, marking the dawn of a new era in understanding early galaxy formation. 

“This is just the first of many such galaxies JWST will discover, as we are only starting to use these cosmic microscopes,” noted Maruša Bradač from the University of Ljubljana. 

“Just like microscopes let us see pollen grains from plants, the incredible resolution of Webb and the magnifying power of gravitational lensing let us see the small pieces inside galaxies.”

The team’s findings were made possible through the Webb’s Canadian NIRISS Unbiased Cluster Survey (CANUCS), which includes near-infrared imaging from the NIRCam and spectral data from the NIRSpec microshutter array. 

A window into the early universe

Published in the journal Nature, this research is a critical step toward unraveling the mysteries of galactic evolution. 

By examining the Firefly Sparkle galaxy, scientists are piecing together how small, disorganized galaxies gradually coalesce into the grand structures we see today, like the Milky Way. 

With JWST continuing its mission, many more galaxies like Firefly Sparkle await discovery, promising to deepen our understanding of the early universe.

Image Credit: NASA, ESA, CSA, STScI

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