The galaxy protocluster is question is forming around the recently-discovered Spiderweb galaxy (also known as MRC 1138-262 or PKS 1138-262), an object nearly 10 billion light-years away.
Galaxy clusters contain thousands of galaxies of all ages, shapes and sizes.
They have a mass of about one million billion times the mass of the Sun and form over billions of years as smaller groups of galaxies slowly come together.
Galaxy clusters also contain a vast intracluster medium (ICM) of gas that permeates the space between the galaxies in the cluster. This gas in fact considerably outweighs the galaxies themselves.
Much of the physics of galaxy clusters is well understood. However, observations of the earliest phases of formation of the ICM remain scarce.
Previously, the ICM had only been studied in fully-formed nearby galaxy clusters. Detecting the ICM in distant protoclusters would allow astronomers to catch these clusters in the early stages of formation.
University of Trieste astronomer Luca Di Mascolo and colleagues were keen to detect the ICM in a protocluster from the early stages of the Universe.
“Cosmological simulations have predicted the presence of hot gas in protoclusters for over a decade, but observational confirmations has been missing,” said Dr. Elena Rasia, a researcher at the Italian National Institute for Astrophysics.
“Pursuing such key observational confirmation led us to carefully select one of the most promising candidate protoclusters.”
That was the Spiderweb protocluster, located at an epoch when the Universe was only 3 billion years old.
Despite being the most intensively studied protocluster, the presence of the ICM has remained elusive.
Finding a large reservoir of hot gas in the Spiderweb protocluster would indicate that the system is on its way to becoming a proper, long-lasting galaxy cluster rather than dispersing.
The study authors detected the ICM of the Spiderweb protocluster through what’s known as the thermal
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