An article published in the journal “Nature” reports the results of the study of a primordial galaxy that has characteristics similar to those attributed to the Milky Way shortly after its formation. A team of researchers led by Lamiya Mowla of Wellesley College in Massachusetts nicknamed it Firefly Sparkle after observing it using the James Webb Space Telescope and with the help of a gravitational lens within the Canadian Unbiased Cluster Survey (CANUCS) with the NIRCam and NIRSpec instruments. The observations also included two companions, two galaxies that appear to be gravitationally bound to Firefly Sparkle.
The image (NASA, ESA, CSA, STScI, C. Willott (NRC-Canada), L. Mowla (Wellesley College), K. Iyer (Columbia)) shows on the left the galaxy cluster MACS J1423.8 + 2404 with a zoom of the area in which the Firefly Sparkle galaxy and its companions are located.
The Milky Way is estimated to be around 13.6 billion years old but the margin of error is considerable. It’s not easy to reconstruct its history, also because we know its early phases only indirectly, by observing primordial galaxies with similar characteristics. Massive primordial galaxies are known, much larger than the Milky Way right after its formation.
A galaxy with a mass similar to that estimated for the newborn Milky Way was discovered in the galaxy cluster MACS J1423.8 + 2404, or simply MACS 1423, during the CLASH survey conducted with the Hubble Space Telescope but the available instruments offered only imprecise information. The James Webb went much further and offered new details. The nickname Firefly Sparkle is due to the bright light emissions from its star clusters, which are reminiscent of those of fireflies.
Even for the extraordinary NIRCam (Near-InfraRed Camera) and NIRSpec (Near-Infrared Spectrograph) instruments, the best that infrared astronomy can offer, it was possible to observe the faint light coming from a small galaxy such as Firefly Sparkle only thanks to a gravitational lens. This made it possible to study this primordial galaxy and two other galaxies that are almost certainly gravitationally bound to it.
Firefly Sparkle’s shape was distorted by the gravitational lensing and had to be reconstructed. The researchers identified 10 distinct star clusters within it, a remarkable feat made possible by the gravitational lensing’s magnification.
Firefly Sparkle’s companion galaxies, nicknamed “Firefly’s Best Friend” and “Firefly’s New Best Friend,” are about 6,000 and 40,000 light-years away from it, respectively. They are astronomically very close to it, considering that the Large Magellanic Cloud is about 160,000 light-years from the Milky Way and the Sun is about 26,000 light-years from the Milky Way’s center. The researchers suspect that Firefly Sparkle’s two companions are orbiting it, but long-term observations are needed to see their movements.
The researchers keep on analyzing data collected on various primordial galaxies to gather all the information useful to improve our models about their formation and evolution. Follow-up studies of Firefly Sparkle and its companions can show their interactions, which may have led at some point to their merger, just as the Milky Way swallowed other small nearby galaxies in the distant past. We see this trio as it was when the universe was about 600 million years old, so we’re seeing and will see events from a very distant past.
