October 19, 2018

  • Cosmic supercluster is largest object ever seen in the early universe

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    The Hyperion supercluster. The blue cloud represents the likely position of the structure’s dark matterESO/L. Calçada & Olga Cucciati et al.   Home News Space  Daily news  17 October 2018

    By Douglas Heaven

    Giants have been around far longer than we thought. A survey of the early universe has revealed a gigantic structure that formed just two billion years after the big bang. Its existence could teach us more about how the universe developed and hints at how much dark matter was around at the time.

    The half-formed supercluster of galaxies, nicknamed Hyperion after a Titan from Greek mythology, is the largest object ever seen from that epoch. Peering into deep space is effectively looking into the past, because of the time it takes for light to travel from distant corners of the cosmos.

    Hyperion’s mass – calculated to be one million billion times that of the sun – puts it in the same league as the largest structures in the universe today, but those have had many more billions of years to grow as gravity pulled them together.

    Pieces of the supercluster had been spotted before, but astronomers had not realised that they were looking at parts of a much larger whole. Very little light reaches us from the early universe, so most sky surveys focus only on small patches at a time.

    Using the VIMOS instrument on the European Southern Observatory’s Very Large Telescope – a tool that lets astronomers take a more panoramic view of very distant regions of space – a team led by Olga Cucciati at the National Institute for Astrophysics in Bologna, Italy, were able to join the dots.

    It makes sense that gigantic superclusters were around way back then, says Cucciati. “These things must be born somewhere, they don’t come out of the blue.” Yet they were still surprised when Hyperion emerged out of the mosaic of smaller objects. “It was great to discover it,” she says.

    Finding such a massive supercluster so soon after the big bang will let us test our theories of how the universe evolved. Any explanation of how gravity pulled matter together into denser and denser objects will now need to account for how very large structures like Hyperion were able to form relatively early on.

    And since gravity acts mainly on dark matter, which makes up 85 per cent of the matter in the universe, studying Hyperion should help reveal how much was around in the universe’s youth, says Cucciati. We are used to looking at galaxies and superclusters when they are fully formed, she says. “This lets us look at things while they are still happening.”