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Discovery of the largest cluster of galaxies known in the early universe

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Researchers using the Gran Telescopio Canarias claim to have isolated the most densely populated cluster of forming galaxies in the early universe. Their work is published in Monthly notices from the Royal Astronomical Society.

Clusters of galaxies are associations of several galaxies linked together by gravity. These gigantic structures can have several thousand entities each. The Virgo cluster, which is integrated into the center of the supercluster which bears the same name and of which the Milky Way is a part, counts for example more than 2,000 galaxies visible.

To understand the evolution of these “galactic cities”, scientists are looking for structures forming in the early universe. One of these clusters has just been spotted over 12.5 billion light years of the earth.

The most massive in the early universe

In 2012, a team of astronomers accurately determined the distance to the galaxy HDF850.1. It is one of the objects with the highest star formation rate in the observable universe. To their surprise, the researchers then discovered that this galaxy was part of a group of a dozen protogalaxies formed during the first billion years of cosmic history.

As part of a recent study, researchers from the Institute of Astrophysics of the Canaries used the OSIRIS instrument, installed on the Gran Telescopio Canarias, to analyze the physical properties of this system. According to this work, it would indeed be the cluster the most massive ever detected in the early universe.

Structurally, astronomers have also made a discovery. “Surprisingly, we have found that all of the cluster members studied so far, about two dozen, are normal star-forming galaxies and that the central galaxy seems to dominate star production in this structure“, Explains Rosa Calvi, former postdoctoral researcher at the IAC and main author of the article.

The cluster of galaxies studied 12.5 billion light years away. Circles indicate newly discovered members. Four of them are shown in detail. Credit: NASA / ESA / Daniel López / IAC

Astronomers predict that this structure, a true “city under construction”, will gradually change until it becomes a cluster of galaxies similar to that of Virgo.

Note that if this cluster appears very massive to us, it is not the oldest ever isolated. In 2019, a team of astronomers had indeed detected a cluster formed 13 billion years ago, when the Universe had only 6% of his current age. This incredible discovery was made possible thanks to three of the most powerful telescopes in the world: Subaru, Keck and Gemini.


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