Massive, well-developed galaxies existed in the early universe, a surprising discovery given expectations of smaller, younger galaxies at that time. A team led by Austrian astrophysicist Nikolaus Sulzenauer has now demonstrated in research published in “The Astrophysical Journal” how dozens of galaxies rapidly merged just 1.4 billion years after the Big Bang to form a giant elliptical galaxy.
Over the past two decades, astronomers have been surprised by the discovery of elliptical galaxies with older stars and very little cold gas – the material needed to form new stars – that originated only a few billion years after the Big Bang. Existing models describing the formation of structures in the cosmos haven’t been able to fully explain this phenomenon.
The research team, including Sulzenauer and Axel Weiß from the Max Planck Institute for Radio Astronomy (MPIfR), used the Atacama Large Millimeter/Submillimeter Array (ALMA) radiotelescope in Chile to observe the cold gas and dust in the center of the 1.4-billion-year-old protocluster “SPT2349-56.” Protoclusters are expansive precursor structures to galaxy clusters with high matter density from the early universe.
The ALMA data showed “how an extremely compact group of 40 galaxies interact simultaneously and collapse towards a common center,” Sulzenauer explained. The structures with the highest densities had to have already decoupled from the expansion of the universe at just ten percent of its age (13.8 billion years old) and rapidly formed this protocluster with collapsing structures. The gas compressed by the collapse and the resulting star formation is revealed in “a cosmic, incredibly bright fireworks display in the distant infrared and millimeter range.”
Every 40 Minutes a New Star
According to the researchers, the observed protocluster “SPT2349-56” holds the record for the most active star factory. In its center, they found four closely interacting galaxies that produce a star every 40 minutes. By comparison, it currently takes a year for three to four stars to form in the Milky Way.
“This quartet of galaxies is ejecting huge, coherent tidal arms at a speed of 300 kilometers per second, extending over an area much larger than the Milky Way,” Sulzenauer stated. The gas clumps in the arms are strung together like pearls on a necklace and surround the core of the protocluster. “To our surprise, these clumps are connected to 20 other galaxies located in the outer areas of the collapsing structure, suggesting a common origin,” Sulzenauer added.
Cascading Merger
For the first time, astronomers have observed the beginning of such a cascading merger. Instead of slowly accumulating mass over billions of years, as previously thought, most of the 40 gas-rich galaxies in the protocluster are expected to be destroyed and ultimately form a single, giant elliptical galaxy within the cosmically short timeframe of less than 300 million years. This discovery offers new insights into how large elliptical galaxies formed in the early universe.
The research team emphasizes that It’s still too early to claim a complete understanding of the early childhood of massive elliptical galaxies. However, significant progress has been made in understanding the connection between the tidal arms in protoclusters and the formation process of massive galaxies.
(S E R V I C E – https://doi.org/10.3847/1538-4357/ae2ff0)
