Astronomers unravel mystery of galaxy cluster formation with ALMA observatory

A pivotal moment in the early universe's history is revealed.
Kavita Verma
Scientists discover cluster of galaxies from the early Universe
Researchers discover new cluster galaxies born in the early Universe.

ESO/Di Mascolo et al/Hubble/H. Ford 

Astronomers have discovered a large reservoir of hot gas in the still-forming galaxy cluster around the Spiderweb galaxy using the Atacama Large Millimeter/submillimeter Array (ALMA). This groundbreaking finding is the most distant detection of such hot gas yet and provides critical insights into the early formation of galaxy clusters.

Galaxy clusters, hosting thousands of galaxies, are among the largest known objects in the Universe. They contain an intracluster medium (ICM) of gas that considerably outweighs the galaxies themselves. Until now, the ICM had only been studied in fully-formed nearby galaxy clusters. Detecting the ICM in distant protoclusters—still-forming galaxy clusters—offers a glimpse into their early formation stages.

Led by Luca Di Mascolo, a researcher at the University of Trieste, Italy, the team aimed to detect the ICM in a protocluster from the early Universe. They focused on the Spiderweb protocluster, located when the Universe was only 3 billion years old. Di Mascolo's team detected the ICM through the thermal Sunyaev-Zeldovich (SZ) effect, which occurs when light from the cosmic microwave background passes through the ICM.

The team discovered that the Spiderweb protocluster contains a vast reservoir of hot gas at tens of millions of degrees Celsius. Although cold gas had been previously detected in this protocluster, the mass of the hot gas found in this new study outweighs it thousands of times.

This finding suggests that the Spiderweb protocluster is on its way to becoming a massive galaxy cluster in around 10 billion years, growing its mass by at least a factor of ten.

Does a revolution await?

Tony Mroczkowski, a co-author of the study and researcher at ESO, explains that "this system exhibits huge contrasts. The hot thermal component will destroy much of the cold component as the system evolves, and we are witnessing a delicate transition." He concludes that "it provides observational confirmation of long-standing theoretical predictions about the formation of the largest gravitationally bound objects in the Universe."

The results provide the valuable groundwork for collaborations between ALMA and ESO's upcoming Extremely Large Telescope (ELT), revolutionizing the study of structures like the Spiderweb. With its state-of-the-art instruments, the ELT will be able to peer into protoclusters and provide detailed information about the galaxies in them.

Together with ALMA's capabilities to trace the forming ICM, this will provide a crucial glimpse into the assembly of some of the largest structures in the early Universe.

Atacama Large Millimeter/submillimeter Array (ALMA)

ALMA is an international astronomy facility. Its partnership includes ESO, the US National Science Foundation, and the National Institutes of Natural Sciences of Japan in collaboration with the Republic of Chile. ALMA construction and operations are led by ESO on behalf of its Member States, by the National Radio Astronomy Observatory in North America, and by the National Astronomical Observatory of Japan in East Asia.

The ALMA Observatory's groundbreaking discovery of a hot gas reservoir in the early formation of galaxy clusters is a significant step forward in understanding the evolution of cosmic structures. This discovery provides a glimpse into the early Universe's history, revealing how galaxy clusters begin to form and grow. ALMA's unprecedented resolution and sensitivity make it the only facility capable of performing such a measurement for the distant progenitors of massive clusters, paving the way for future discoveries in the field of astrophysics.

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