The sky region of the galaxies at a distance of about 13.5 billion light-years from the Earth. Blue circles mark individual galaxies, whilst the green rectangle indicates the bright radio galaxy located at the same distance. (Image credit: European Southern Observatory.) Using the ESO Very Large Telescope (VLT), a team of astronomers from The Netherlands, Germany, France and the USA have discovered the most distant group of galaxies ever seen, about 13.5 billion light-years away from our Milky Way galaxy.

They detected the galaxies after observing the area of sky around a galaxy which is a strong source of radio waves. 'Radio galaxies’ of this type are often very luminous in visible light meaning they can be seen by optical telescopes at large distances. They are frequently found at the centre of forming clusters of galaxies, which provided a strong clue that this galaxy cluster would be found in the vicinity.

The cluster of galaxies is observed as it was at a time when the Universe was only about 10% of its present age because it has taken the light now recorded by the VLT about nine-tenths of the age of the Universe to travel this huge distance. By combining the number of detected galaxies and the observed volume of the structure, its estimated mass is 1000 million million (1015) times the mass of the Sun - this is comparable with the masses of nearby galaxy clusters in the present-day Universe.

This newly discovered group of galaxies is the most distant discovered so far and hence the earliest known at this moment. The astronomers conclude that this group of early galaxies will develop into a rich cluster of galaxies, such as those seen in the nearby present-day Universe. The discovery of the structure provides one of the best clues so far for studying the formation of clusters of galaxies from the gas produced in the Big Bang, a significant puzzle of modern cosmology.