Domes on the summit of Mauna Kea.

Observations by the Subaru telescope (silver and white) helped to pinpoint a primordial cluster of 12 galaxies. Credit: NAOJ

Astronomy and astrophysics

A galactic grouping dates to the dawn of the Universe

Telescopes detect a ‘protocluster’ that had already formed less than one billion years after the Big Bang.

Astronomers have found the earliest known protocluster — a mass of gas that contains the seeds of a cluster of galaxies.

Insights into how galaxy clusters form could help scientists understand the evolution of structure in the Universe. But many of the clusters near the Milky Way have already matured, making it difficult to spot these bodies in their early stages. This has led astronomers to search for distant protoclusters from the early universe.

A team led by Yuichi Harikane, at the University of Tokyo, used the Subaru telescope at the summit of Mauna Kea, Hawaii, to look for regions of the night sky with more galaxies than expected. The researchers made follow-up observations of one such region to measure how far away its galaxies were, thereby mapping them in 3D.

This revealed a protocluster of a dozen galaxies that existed 13 billion years ago, less than one billion years after the Big Bang — making it the earliest known protocluster of that size.

Further analysis showed that its galaxies are forming stars at a rate at least five times faster than the average for galaxies with similar masses.