Dec 11

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

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 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. Credits Image: NASA, ESA, CSA, STScI, Chris Willott (NRC-Canada), Lamiya Mowla (Wellesley College), Kartheik Iyer (Columbia)

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.

“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.

“Without the benefit of this gravitational lens, we would not be able to resolve this galaxy,” said Kartheik Iyer, a 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 show 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.

Read more on the Webb Telescope website.