The ‘Sparkler’ galaxy was discovered in 2022 using some of the first data from the NASA/ESA/CSA James Webb Space Telescope.
It is strongly magnified by a factor of up to 100 by SMACS J0723.3-7327, a massive cluster of galaxies within the southern constellation of Volans.
The Sparkler has a redshift of z=1.378, meaning we are seeing it as it existed approximately 9.1 billion years ago.
It is embedded in a system of globular clusters (dubbed ‘sparklers’) and satellite galaxies, and appears to be swallowing them as it grows.
“Globular clusters are dense collections of around a million stars,” said Swinburne University’s Professor Duncan Forbes and San Jose State University’s Professor Aaron Romanowsky.
“The Milky Way is currently host to around 200 globular clusters.”
In the study, the astronomers examined the age and metallicity distribution of globular clusters surrounding the Sparkler galaxy to determine that they resemble younger versions of the clusters now around the Milky Way.
Several have old formation ages and are metal-rich similar to those seen in the bulge of the Milky Way and so are likely to be globular clusters.
A couple of star clusters had intermediate ages and were metal-poor — these clusters are associated with the satellite galaxy that is being accreted onto the Sparkler galaxy.
It appears to be swallowing up this satellite galaxy and its system of globular clusters, just like the Milky Way has done in the past.
Although the Sparkler is currently only 3% the mass of the Milky Way, it is expected to grow over cosmic time to match the Milky Way’s mass in the present day Universe.
“We appear to be witnessing, first hand, the assembly of this galaxy as it builds up its mass — in the form of a dwarf galaxy and several globular clusters,” Professor Forbes said.
“We are excited by this unique opportunity to study both the formation of globular clusters, and an infant Milky Way, at a time when the Universe was only 1/3 of its present age.”
“The origin of globular clusters is a long-standing mystery, and we are thrilled that Webb can look back in time to see them in their youth,” Professor Romanowsky said.