Galaxy clusters are gravitationally bound groups of thousands of galaxies, which themselves each contain hundreds of billions of stars. The clusters grow bigger and bigger over time as they acquire new members.

To find how these clusters evolve over time and what they looked like billions of years ago, astronomers looked back in time to our youthful universe.

Since light takes time to reach us, we can see very distant objects as they were in the past.

We can see the newly found galaxy cluster – called Massive Overdense Object (MOO) J1142+1527 - as it existed 8.5 billion years ago, long before Earth formed.

As light from remote galaxies makes its way to us, it becomes stretched to longer, infrared wavelengths by the expansion of space.

That is where NASA's Spitzer Space Telescope and Wide-field Infrared Survey Explorer (WISE) helped out.

Astronomers first combed through the WISE catalogue to find candidates for clusters of distant galaxies. WISE catalogued hundreds of millions of objects in images taken over the entire sky from 2010 to 2011.

They then used Spitzer to narrow in on 200 of the most interesting objects, in a project named the 'Massive and Distant Clusters of WISE Survey', or MaDCoWS.

"It's the combination of Spitzer and WISE that lets us go from a quarter billion objects down to the most massive galaxy clusters in the sky," said lead author Anthony Gonzalez of the University of Florida in US.

The WM Keck Observatories and Gemini Observatory on Mauna Kea in Hawaii were used to measure the distance to the cluster at 8.5 billion light-years.

Using data from the Combined Array for Research in Millimeter-wave Astronomy (CARMA) telescopes in US, the scientists were then able to determine that the cluster's mass is a quadrillion times that of our Sun - making it the most massive known cluster that far back in space and time.

MOO J1142+1527 may be one of only a handful of clusters of this heft in the early universe, scientists said.

The study was published in the the Astrophysical Journal Letters.

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