Clusters of galaxies are the largest building blocks in the universe. Our galaxy, the Milky Way, is part of the Virgo cluster, comprising some 1000-2000 galaxies. By observing galaxies and clusters that are very distant from Earth, astronomers can look back in time, as their light was sent out a long time ago and took millions or billions of light-years to reach the astronomers’ telescopes.

An international team of astronomers from Germany and Japan has discovered the most distant cluster of galaxies known so far — 9.6 billion light years away. The X-ray and infrared observations showed that the cluster hosts predominantly old, massive galaxies, demonstrating that the galaxies formed when the universe was still very young. These and similar observations therefore provide new information not only about early galaxy evolution but also about history of the universe as a whole.

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