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Found: First Actively Forming Galaxy as Lightweight as Young Milky Way

Hundreds of overlapping objects at various distances are spread across this field. Galaxies’ colors vary. The majority appear orange, pink, and white, some are shades of orange or blue. Most galaxies appear as fuzzy ovals, but a few have distinctive spiral arms. At the very center is a tiny galaxy nicknamed Firefly Sparkle that looks like a long, angled, dotted line. Smaller companions are nearby.

Hundreds of overlapping objects at various distances are spread across this field. At the very center is a tiny galaxy nicknamed Firefly Sparkle that looks like a long, angled, dotted line. Smaller companions are nearby.

Credits: NASA, ESA, CSA, STScI, Chris Willott (National Research Council Canada), Lamiya Mowla (Wellesley College), Kartheik Iyer (Columbia University)

For the first time, NASA’s James Webb Space Telescope has detected and “weighed” a galaxy that not only existed around 600 million years after the big bang, but is also similar to what our Milky Way galaxy’s mass might have been at the same stage of development. Other galaxies Webb has detected at this time period are significantly more massive. Nicknamed the Firefly Sparkle, this galaxy is gleaming with star clusters — 10 in all — each of which researchers examined in great detail.

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

A frame split horizontally down the middle. At left is a galaxy cluster and background galaxies, showing thousands of overlapping objects at various distances. The background is black. The galaxies’ colors vary, including white, pink, orange, and blue. Most galaxies appear as ovals or dots. Just above center is a bright white oversized oval, a supergiant elliptical galaxy. Around it are many thin, long orange or pink arcs. These are background galaxies that appear stretched and distorted. To the bottom right is the outline of a small box. On the right side is a zoomed in view of this area. There are two smaller circular outlines flanking a larger central oval outline, labeled Firefly Sparkle galaxy. Within it is a long line, pointing from bottom left to top right with 10 circular star clusters in pink, purple, and blue. The circled galaxy to the bottom left is labeled Companion 1 and looks like a bright red dot. At top right, the circled galaxy labeled Companion 2 is lighter red and surrounded by a red disk.

For the first time, astronomers using NASA’s James Webb Space Telescope have identified a galaxy, nicknamed the Firefly Sparkle, that not only is in the process of assembling and forming stars around 600 million years after the big bang, but also weighs about the same as our Milky Way galaxy if we could “wind back the clock” to weigh it as it developed. Two companion galaxies are close by, which may ultimately affect how this galaxy forms and builds mass over billions of years.

NASA, ESA, CSA, STScI, Chris Willott (National Research Council Canada), Lamiya Mowla (Wellesley College), Kartheik Iyer (Columbia University)

“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 our own galaxy’s when it was in the process of forming,” said Lamiya Mowla, co-lead author of the paper and an assistant professor at Wellesley College in Massachusetts. “There is so much going on inside this tiny galaxy, including so many different phases of star formation.”

Webb was able to image the galaxy in crisp detail for two reasons. One is a benefit of the cosmos: A massive foreground galaxy cluster radically enhanced the distant galaxy’s appearance through a natural effect known as gravitational lensing. And when combined with the telescope’s specialization in high-resolution infrared light, Webb delivered unprecedented new data about the galaxy’s contents.

Image B: Galaxy Cluster MACS J1423 (NIRCam Image)

Thousands of overlapping objects at various distances are spread across this field, including galaxies in a massive galaxy cluster and distorted background galaxies behind the galaxy cluster. The background of space is black. The galaxies’ colors vary. The majority appear white or pink, some are shades of orange or blue. Most galaxies appear as fuzzy ovals, but a few have distinctive spiral arms. The most distant galaxies are the tiniest and appear as red dots or smudges. Several foreground stars with eight diffraction spikes appear as large as some of the smaller galaxies. Just above center is a very bright white, oversized oval, angled at 45 degrees and pointing to the top left and bottom right. This is a supergiant elliptical galaxy. Immediately around it are many thin, long, orange or pink arcs. They follow invisible concentric circles that curve around the center. These are background galaxies that have been stretched and distorted.

In this image from NASA’s James Webb Space Telescope, thousands of glimmering galaxies are bound together by their own gravity, making up a massive cluster formally classified as MACS J1423. The largest, bright white oval is a supergiant elliptical galaxy. The galaxy cluster acts like a lens, magnifying and distorting the light of objects that lie well behind it, an effect known as gravitational lensing.

NASA, ESA, CSA, STScI, Chris Willott (National Research Council Canada), Lamiya Mowla (Wellesley College), Kartheik Iyer (Columbia University)

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

Mowla, who spotted the galaxy in Webb’s image, was drawn to its gleaming star clusters, because objects that sparkle typically indicate they are extremely clumpy and complicated. Since the galaxy looks like a “sparkle” or swarm of lightning bugs on a warm summer night, they named it the Firefly Sparkle galaxy.

Reconstructing the Galaxy’s Appearance

The research team modeled what the galaxy might have looked like if it weren’t stretched and discovered that it resembled an elongated raindrop. Suspended within it are two star clusters toward the top and eight toward the bottom. “Our reconstruction shows that clumps of actively forming stars are surrounded by diffuse light from other unresolved stars,” said Iyer. “This galaxy is literally in the process of assembling.”

Webb’s data shows the Firefly Sparkle galaxy is on the smaller side, falling into the category of a low-mass galaxy. 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 witnessing a galaxy being assembled brick by brick,” Mowla said.

Stretched Out and Shining, Ready for Close Analysis

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, purple, and blue. Those colors in Webb’s images and its supporting 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 universe,” said Chris Willott from the National Research Council of Canada’s Herzberg Astronomy and Astrophysics Research Centre, a co-author and the observation program’s principal investigator. “Each clump of stars is undergoing a different phase of formation 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.

Image C: Illustration of the Firefly Sparkle Galaxy in the Early Universe (Artist’s Concept)

An illustration of what the Firefly Sparkle galaxy might have looked like when it existed in the early universe. The horizontal frame has a black background. The galaxy is in the middle, beginning in a triangle at the top, forming two wider points toward the lower center, and coming to a rounder point at the bottom, forming a rough parallelogram. There are tiny white stars throughout the galaxy, which appear in hazy layers. There are 10 separate, prominent round star clusters, which each have bright colors. Toward the top is a bright blue star cluster. Below that is a purple star cluster. The majority of the star clusters are close to one another just below center, and appear in oranges, pinks, white, and blue. The star clusters are the brightest sections of the overall galaxy. Its other diffuse areas of white stars are dimmer. At the bottom right are the words, Artist’s Concept.

This artist concept depicts a reconstruction of what the Firefly Sparkle galaxy looked like about 600 million years after the big bang if it wasn’t stretched and distorted by a natural effect known as gravitational lensing. This illustration is based on images and data from NASA’s James Webb Space Telescope.

Illustration: NASA, ESA, CSA, Ralf Crawford (STScI). Science: Lamiya Mowla (Wellesley College), Guillaume Desprez (Saint Mary's University)

Video: “Firefly Sparkle” Reveals Early Galaxy

‘Glowing’ Companions

Researchers can’t predict how this disorganized galaxy will build up and take shape over billions of years, but there are two galaxies that the team confirmed are “hanging out” within a tight perimeter and may influence how it builds mass over billions of years.

Firefly Sparkle is only 6,500 light-years away from its first companion, and its second companion is separated by 42,000 light-years. For context, 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 researchers 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 interactions and mergers with other tinier galaxies,” said Yoshihisa Asada, a co-author and doctoral student at Kyoto University in Japan. “We might be witnessing this process in action.”

The team’s research relied on data from 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). The CANUCS data intentionally covered a field that NASA’s Hubble Space Telescope imaged as part of its Cluster Lensing And Supernova survey with Hubble (CLASH) program.

This work has been published on December 11, 2024 in the journal Nature.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).