An analysis of some of the first data from the Webb Space Telescope has revealed a galaxy that mirrors the most primitive version of our galaxy, the Milky Way. The galaxy, dubbed “Sparkler,” is embedded in a system of globular clusters and satellite galaxies, and appears to be swallowing them as it grows. The research has been published in the Monthly Notices of the Royal Astronomical Society.
Sparkler, named for its two dozen orbiting globular clusters, provides unique insight into the history of the Milky Way’s formation during its infancy. Globular clusters are dense collections of about a million stars. The Milky Way is currently home to about 200 globular clusters.
Twinkling is located in the constellation of Volans, in the southern sky. The galaxy and its globular cluster system have been detected at a redshift of 1.38, which implies that we are viewing the galaxy about 9 billion years ago, about 4 billion years after the Big Bang. The observations have been possible thanks to the Webb and the effect of brightness of a gravitational lens, aligned fortuitously in front of the galaxy.
The research was led by Professor Duncan Forbes, from Swinburne University (Australia), and Professor Aaron Romanowsky, from San Jose State University (USA). They examined the age and metallicity distribution of a dozen compact star clusters surrounding Sparkler to determine that they resemble younger versions of the clusters now surrounding the Milky Way.Several have old formation ages and are rich in metals, similar to those observed in the bulge of the Milky Way, so they are likely globular clusters.
A couple of star clusters were intermediate in age and metal poor: these clusters are associated with the satellite galaxy that is adhering to the Sparkler galaxy; it appears to be swallowing this satellite galaxy and its globular cluster system, just as the Milky Way has done in the past.
Although Sparkler is currently only 3% the mass of the Milky Way, it is expected to grow with cosmic time to equal the mass of the Milky Way in the universe today. The team will need deeper images to detect more clusters and satellites around Sparkler.
“It appears that we are witnessing, firsthand, the assembly of this galaxy as its mass increases, in the form of a dwarf galaxy and several globular clusters,” Professor Forbes said in a statement. He adds: “We are excited about this unique opportunity to study both globular cluster formation and a fledgling Milky Way, at a time when the Universe was only 1/3 of its current age.”
Professor Aaron Romanowsky, co-author of the study, comments: “The origin of globular clusters has been a longstanding mystery, and we are delighted that Webb can look back in time to see them in his youth.”