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Astronomers discover the granddaddy of galaxy clusters

The most massive conglomeration of galaxies ever spotted in the early universe has been found, astronomers say.
Image: Infrared/optical representative-color image of a massive galaxy cluster
An infrared/optical representative-color image shows a massive galaxy cluster located 7 billion light-years from Earth. Galaxies with "old" stellar populations are circled in yellow; galaxies with "young" stellar populations are circled in blue.NASA /JPL-Caltech / CfA / CTIO Blanco / LMU Munich
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The most massive conglomeration of galaxies ever spotted in the early universe has been found, astronomers say.

This behemoth galaxy cluster contains about 800 trillion suns packed inside hundreds of galaxies. And it's not even finished growing.

The newfound cluster, called SPT-CL J0546-5345, is about 7 billion light-years from Earth, meaning that its light has taken that long to reach us. Thus, astronomers are seeing this clump as it was 7 billion years ago.

By now, it likely will have quadrupled in size, researchers said. The universe is about 13.7 billion years old.

"This galaxy cluster wins the heavyweight title," astronomer Mark Brodwin of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., said in a statement. "It's among the most massive clusters ever found at this distance."

While there are some heavier clusters in the near universe, if we could see this cluster as it is today, it would likely rank among the most massive clusters of all, the researchers said.

Brodwin and colleagues reported the discovery in a recent edition of the Astrophysical Journal.

Dark energy
The discovery could help scientists piece together the early history of our universe, as well as how strange stuff called dark energy played a role.

Seven billion years ago, our solar system which is about 4.5 billion years old was not yet born. This cluster must have formed relatively soon after the Big Bang to have amassed such a girth so early, scientists said.

"This cluster is full of 'old' galaxies, meaning that it had to come together very early in the universe's history within the first 2 billion years," Brodwin said.

These days, new galaxy clusters cannot form because of the universe's accelerating rate of expansion each galaxy is flying apart from all others at ever-increasing speeds. This is thought to be caused by a mysterious force scientists have named dark energy.

Scientists think dark energy is behind the universe's mysteriously accelerating expansion, but they can't establish for sure that this force exists.

Weighing massive clusters like SPT-CL J0546-5345 could help astrophysicists pin down the nature of this odd quantity.

South Pole vision
The galaxy cluster was spotted by a new, huge 33-foot (10-meter) telescope at the South Pole, where the observatory benefits from an exceptionally clear, dry and stable atmosphere that enables extremely crisp high-resolution photos.

The so-called South Pole Telescope, funded by the National Science Foundation and run by scientists at more than a dozen international institutions, is finishing up its first survey of a huge swath of the sky in relatively long-wavelength, low-frequency submillimeter light.

Once the survey is complete, the researchers hope to find many more previously unknown giant galaxy clusters.

"After many years of effort, these early successes are very exciting," Brodwin said. "The full SPT survey, to be completed next year, will rewrite the book on the most massive clusters in the early universe."