Astronomers using the South Pole Telescope report that they have discovered the most massive galaxy cluster ever. It lies at a distance of around 7 billion light-years away.
In fact there are several galaxies located in one find. The cluster designated SPT-CL J0546-5345 weighs in at over 800 trillion Suns and the huge find said to number hundreds of galaxies has old stellar populations, like modern-day ellipticals and young stellar populations, like modern-day spirals.

Mark Brodwin, a Smithsonian astronomer at the Harvard-Smithsonian Center for Astrophysics explains just how huge a find this actually is:
This galaxy cluster wins the heavyweight title. It's among the most massive clusters ever found at this distance. It's like discovering a skyscraper in ancient Rome.

Its sheer distance is about 7 billion light-years, meaning we see it as it appeared 7 billion years ago, when the universe was half as old as now and our solar system didn't exist yet. Even at that young age, the cluster was almost as massive as the nearby Coma cluster as reported in the Daily Galaxy. Since then it will have grown around four times larger than what we are seeing it today which means this is the most massive galaxy cluster in the universe.

Mr Brodwin, along with colleagues from the South Pole Telescope (SPT). The SPT is just completing its pioneering millimeter-wave survey of a huge swath of sky covering 2,500 square degrees. The aim of the SPT survey is to find a large sample of massive galaxy clusters in order to measure the equation of state of the dark energy. This characterises cosmic expansion and how quickly the universe is inflating.

Once this distant cluster was found, the team looked deeper using an infra-red array camera on the Spitzer Space Telescope in order to pinpoint galaxies within the cluster. Detailed observations of the galaxies' speeds with the Magellan telescopes in Chile proved that the galaxy cluster was indeed a heavyweight.
The team fully expects to find many more giant galaxy clusters lurking in the distance once the survey at the South Pole Telescope is completed.

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