Named SPT-CL J2215-3537, or SPT2215 for brevity, the cluster is an astonishing 8.4 billion light-years away.
In a pioneering discovery, astronomers spot the most distant “relaxed” galaxy cluster yet, untouched by turbulent clashes with other galactic groups. This finding lays the groundwork for understanding the universe’s structure and its evolution over billions of years.
To unearth this far-flung, youthful, relaxed, most distant galaxy cluster, scientists made use of data from NASA’s Chandra X-ray Observatory, the now-retired Spitzer Space Telescope, the South Pole Telescope, and the Dark Energy Survey project in Chile. The findings are documented in a series of three research papers.
Most Distant “Relaxed” Galaxy Cluster
Named SPT-CL J2215-3537, or SPT2215 for brevity, the cluster is an astonishing 8.4 billion light-years away. Its early existence—when the universe was only 5.3 billion years old, versus its current 13.8 billion—suggests that it matured quicker than its peers and has spent the last billion years in relative tranquility. Astronomers estimate SPT2215’s mass to be an astronomical 700 trillion times that of the sun.
Galaxy clusters, a spectacular amalgamation of tens to hundreds of galaxies, hot gas, and dark matter, evolve over time by merging with other clusters, causing fluctuations in the cluster’s gas. However, the gas can attain a serene, smooth texture when given enough time to “relax” without a merger.
A Space Oddity: The Silent Cluster SPT2215
“Until now, we haven’t seen a relaxed galaxy cluster as distant as SPT2215,” said Michael Calzadilla of MIT, lead author of one of the papers, which confirmed the cluster’s relaxed status and outlined its key properties.
The center of SPT2215 harbors a massive galaxy with a colossal black hole. Calzadilla’s paper found extensive new star formation within this central galaxy. The cluster’s relaxed state allows the hot gas to cool down, providing conducive conditions for star formation.
The Role of Black Holes in Star Formation
The giant black hole at the heart of the cluster influences the rate at which the gas cools to form stars. If the black hole drives too many potent outbursts, most of the cluster’s gas cannot cool sufficiently to create a surge of new stars. Uniquely, the giant black hole in SPT2215 does not seem to hinder such cooling.
Another intriguing feature of SPT2215 is the solitude of its central galaxy. Its closest peers are about 600,000 light-years away, giving scientists reason to believe that SPT2215 has remained merger-free for approximately the last billion years.
A Galaxy Cluster Defying Expectations
This finding counters prevailing assumptions, as galaxy clusters at this epoch of the universe are typically still growing and undergoing merger-related disruptions. SPT2215’s peaceful state amidst a turbulent universe evokes curiosity. “It’s like discovering a pristine kitchen right after a dinner rush,” said Lindsey Bleem of the Argonne National Laboratory.
“Relaxed clusters like SPT2215 serve as cosmic yardsticks to measure the expansion of the universe,” said Adam Mantz of Stanford University. The discovery of distant objects like this enhances our understanding of cosmic expansion and the dark energy driving it.
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