An international team of researchers studying data from the Atacama Large Millimeter/Submillimeter Array (ALMA) says they are close to solving the decades-old “intergalactic mystery” of how the universe’s largest galaxies were formed.
Unlike flat, disk-shaped galaxies such as the Milky Way, the formation of larger elliptical galaxies described by the researchers as “bulging footballs” has remained a mystery. According to a statement by Dr Qing-Hua Tan from the Purple Mountain Observatory, who led the study, “Astrophysicists have sought to understand this process for decades” but still struggle to explain it.
In this latest research, Dr. Tan and colleagues say their research points to the collision of two disk galaxies as the missing mechanism behind elliptical galactic formation. According to Dr Annagrazia Puglisi from the University of Southampton, who co-authored the study, this proposed mechanism “take(s) us closer to solving a long-standing mystery in astronomy that will redefine our understanding of how galaxies were created in the early universe.”
ALMA Data From Over 100 Galaxies Sheds Light in Intergalactic Mystery
To investigate the mechanism behind the formation of giant galaxies, the researchers tapped into the open-source A3COSMOS and A3GOODSS archival projects. This effort yielded data on over 100 star-forming galaxies collected by the world’s largest radio telescope, ALMA.
The team found a pattern when analyzing the distribution of light emitted by distant and highly luminous galaxies. Unlike disk-like galaxies, elliptical galaxies had a denser concentration of stars at their center. After checking with galactic formation models, this distribution seemed to indicate that the larger galaxies were feeding on a steady stream of “cold gas,” which can fuel star growth.
Still, after accounting for extra fuel, their models said something was missing. After more tweaking, the team found that something much more significant must also be added to the formation of these bulging galaxies. Specifically, they suspected that a collision between disk-like galaxies had caused a chain reaction resulting in the formation of a single, bulging elliptical galaxy.
“Two disk galaxies smashing together caused gas – the fuel from which stars are formed – to sink towards their centre, generating trillions of new stars,” Puglisis explained. “These cosmic collisions happened some eight to 12 billion years ago when the universe was in a much more active phase of its evolution.”
Dr. Tan says this process took place in a relatively short time. This is especially apparent compared to the formation of galaxies we see today.
“These galaxies form quickly – gas is sucked inwards to feed black holes and triggers bursts of stars, which are created at rates ten to 100 times faster than our Milky Way,” Dr. Tan explained.
The result is a bulging galaxy that astronomers describe as spheroid in shape. In their published study, the team notes that based on their analysis, “spheroids are directly generated by star formation within the cores of highly luminous starburst galaxies in the distant Universe.”
“This is the first real evidence that spheroids form directly through intense episodes of star formation located in the cores of distant galaxies,” Dr. Tan said.
Creating The ‘Most Complete’ Map of The Stellar Components of Galaxies
Next, the international research team plans to combine their findings with data captured by instruments mounted on the James Webb Space Telescope, the Euclid satellites, and the Chinese Space Station. Once finished, the team believes this collective dataset will offer the most complete map of the stellar components of galaxies ever assembled.
“This will give us a more complete picture of early galaxy formation and deepen our understanding of how the universe has evolved since the beginning of time,” Puglisi explained.
The study “In situ spheroid formation in distant submillimetre-bright Galaxies” was published in Nature.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.