First Actively Forming Galaxy as Lightweight as Infant Milky Way Found

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

“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 co-lead author of the paper Lamiya Mowla (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.”

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

“Without the benefit of this gravitational lens, we would not be able to resolve this galaxy,” said co-lead author Kartheik Iyer (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 JWST’s image, was drawn to its shining star clusters, as objects that sparkle typically indicate they are extremely complicated and clumpy. Since the galaxy seems like a “sparkle” or swarm of lightning bugs on a warm summer night, they termed it the Firefly Sparkle galaxy.

Reconstructing the Galaxy’s Appearance

The research team modelled what the galaxy may have looked like if it weren’t stretched and found that it resembled a drawn-out raindrop. Suspended within it are 2 star clusters toward the top and 8 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.”

JWST’s data shows the Firefly Sparkle galaxy is on the smaller side, falling into the class of a low-mass galaxy. Billions of years will go by 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,” said Mowla.