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NASA’s James Webb Space Telescope has detected and “weighed” a galaxy – seen 600 million years after the Big Bang – that is similar to what our Milky Way galaxy might have looked like at the same stage of development.

Nicknamed the Firefly Sparkle, this young galaxy is gleaming with star clusters – 10 in all – that may be signs that early galaxies form by fragmenting into giant star clusters, with some surviving today as globular clusters.

The lead co-authors of the study, , are Wellesley College’s Lamiya Mowla and Columbia University’s Kartheik Iyer – both former postdoctoral researchers at the University of Toronto’s .

Roberto Abraham, professor and chair of the David A. Dunlap department of astronomy and astrophysics in U of T’s Faculty of Arts & Science, is also part of the CAnadian NIRISS Unbiased Cluster Survey (CANUCS) team behind the research.

He recently shared his insights on the new discovery with the Faculty of Arts & Science news team.

How is Webb helping us understand things about the universe that we didn’t know before?

Webb’s resolution and sensitivity allows us to study extremely distant objects – like those gleaming star clusters that initially drew us to the Firefly Sparkle galaxy – in crisp detail. We’re also able to “zoom in” due to a natural effect known as strong gravitational lensing. In this case, a galaxy cluster in the foreground enhanced the Firefly Sparkle galaxy behind it, acting like a giant magnifying glass.

With Webb, we can go back in time and look at distant objects like the Firefly Sparkle and see objects in it that may be young globular clusters, which are seen today as dense groups of millions of ancient stars. Witnessing things that are ancient today being born in the distant past is mind-blowing. Seeing 10 of them forming this way makes the Firefly Sparkle a goldmine for understanding the earliest phases of formation and growth in galaxies.

Using Webb’s images and data, the researchers concluded that the Firefly Sparkle had the same mass as our Milky Way galaxy would have if we could “turn back time” to weigh it as it was assembling.

Why is knowing the “weight” of the Firefly Sparkle galaxy important?

It gives us a glimpse of how much young galaxies weighed when the universe was very young. Today’s galaxies are way more massive. We’ve known this for a while, but Webb lets us figure out how they get more massive and how they get so many stars within them. In some models, the stars form slowly via internal processes, while in other models they form in small galaxies that crash together and grow bigger. Galaxies like the Firefly Sparkle tell us that both things are happening, but the latter process is probably dominant.

In 2022, the CANUCS team used Webb to identify the most distant globular clusters known in what they dubbed “the Sparkler galaxy.” How does this new discovery build upon the previous one?

The little points of light – “sparkles” – seen in the Sparkler galaxy we studied in 2022 were four billion years old when their light was emitted, which was similar to the age of the universe then. Nine billion years later, in today’s universe, we know exactly what they look like: today’s globular clusters. With the new Firefly Sparkle galaxy, we’re closer to the starting point of growth, so we’re not 100 per cent sure what the little points of light in the galaxy evolve into.

You could say that looking at the Sparkler galaxy was like looking at a toddler: you’re pretty sure a toddler is going to eventually grow up to look like an adult. But with Firefly Sparkle, it’s like looking at an embryo: all sorts of animals have similar-looking embryos, so in this case what those sparkles turn into is more ambiguous.

What are you excited to look for next with Webb?

It’s more like, what am I not excited to look at next with Webb? All the data and images coming from Webb fill me with a sense of giddy joy – it feels a bit like the universe is letting us in on some pretty big secrets and we’re lucky to be alive right now.

In this case, we need to find more examples of systems similar to the Sparkler and the Firefly Sparkle to be totally confident that these little points of light in the Firefly Sparkle are indeed very young globular clusters. What we’ve got now is a spectacular starting point. Canada has a long history of galaxy formation and globular cluster research, so I look forward to seeing us continue along that path. 

With files from Space Telescope Science Institute/NASA