Scientists find galaxy cluster aged 3 billion years, but still very young

ESO’s Very Large Telescope has discovered the most distant mature cluster of galaxies ever found which is three billion years old.

"We have measured the distance to the most distant mature cluster of galaxies ever found", says the lead author of the study in which the observations from ESO's VLT have been used, Raphael Gobat.

"The surprising thing is that when we look closely at this galaxy cluster it doesn't look young - many of the galaxies have settled down and don't resemble the usual star-forming galaxies seen in the early Universe."

Although even more distant clusters have been seen, they appear to be young clusters in the process of formation and are not settled mature systems.

This grouping, named CL J1449+0856 , had all the hallmarks of being a very remote cluster of galaxies. The results showed that we are indeed seeing a galaxy cluster as it was when the Universe was about three billion years old - less than one quarter of its current age.

Once the team knew the distance, they found evidence suggesting that most of the galaxies in the cluster were not forming stars, but were composed of stars that were already about one billion years old.

X-rays coming from CL J1449+0856 made with ESA's XMM-Newton space observatory also confirmed that this is a mature cluster.

The cluster is giving off X-rays that must be coming from a very hot cloud of tenuous gas filling the space between the galaxies and concentrated towards the centre of the cluster - another sign of a mature galaxy cluster.

"These new results support the idea that mature clusters existed when the Universe was less than one quarter of its current age. Such clusters are expected to be very rare according to current theory, and we have been very lucky to spot one. But if further observations find many more then this may mean that our understanding of the early Universe needs to be revised,” said Gobat.