Four previously unknown galaxy clusters have been discovered, at previously unobservable distanced. The farthest is 10 billion light years from Earth. Each cluster potentially contains thousands of individual galaxies.

An international team of astronomers, led by Imperial College London, used a new method of data analysis from the two European Space Agency satellites, Planck and Herschel, to identify more distant galaxy clusters than has previously been possible. The researchers believe there could be up to 2,000 clusters that were previously too far from Earth to observe. The new observation technique could help to build a more detailed timeline of how clusters are formed.

Galaxy clusters are the most massive objects known, containing hundreds to thousands of galaxies. To discover how these clusters are formed, astronomers need to observe how galaxies looked in the distant past, which means finding observable clusters farther from Earth.

"The light from the most distant of the four new clusters identified by the team has taken over 10 billion years to reach us. This means the researchers are seeing what the cluster looked like when the universe was just 3 billion years old," according to a release announcing the findings.

"Although we're able to see individual galaxies that go further back in time, up to now, the most distant clusters found by astronomers date back to when the universe was 4.5 billion years old. This equates to around 9 billion light years away. Our new approach has already found a cluster in existence much earlier than that, and we believe it has the potential to go even further," explained lead researcher David Clements, from the Department of Physics at Imperial College London.

"Galaxies are divided into two types: elliptical galaxies that have many stars, but little dust and gas; and spiral galaxies like our own, the Milky Way, which contain lots of dust and gas. Most clusters in the universe today are dominated by giant elliptical galaxies in which the dust and gas has already been formed into stars," writes the release. The process of forming dust and gas into stars emits light that can be picked up by Earth's satellite surveys.

"What we believe we are seeing in these distant clusters are giant elliptical galaxies in the process of being formed," said Clements.

The study is published in the Monthly Notices of the Royal Astronomical Society.