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Huge galaxy cluster hints at universe's skeleton

A gigantic, previously unknown set of galaxies has been found in the distant universe, shedding light on the underlying skeleton of the cosmos.
ESO/L. Calçada/Subaru/Nat. Astro. Observatory of Japan/M. Tanaka
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A gigantic, previously unknown set of galaxies has been found in the distant universe, shedding light on the underlying skeleton of the cosmos.

"Matter is not distributed uniformly in the universe," said Masayuki Tanaka, an astronomer with the European Southern Observatory (ESO) who helped discover the galactic assemblage. "In our cosmic vicinity, stars form in galaxies and galaxies usually form groups and clusters of galaxies."

But those collections of matter are just small potatoes compared to larger structures long-theorized to exist.

"The most widely accepted cosmological theories predict that matter also clumps on a larger scale in the so-called 'cosmic web,' in which galaxies, embedded in filaments stretching between voids, create a gigantic wispy structure," Tanaka said.

These filaments are millions of light-years long and constitute the skeleton of the universe: Galaxies gather around them, and immense galaxy clusters form at their intersections, lurking like giant spiders waiting for more matter to digest.

Scientists have struggled, though, to explain how the filaments come into existence. While massive filamentary structures have often been observed at relatively small distances from us, solid proof of their existence in the more distant universe has been lacking until now.

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The team led by Tanaka discovered a large structure around a distant cluster of galaxies in images they had taken earlier. They have now used two major ground-based telescopes to study this structure in greater detail, measuring the distances from Earth to more than 150 galaxies, and, hence, obtaining a three-dimensional view of the structure.

The spectroscopic observations, detailed in the Astronomy & Astrophysics Journal, were performed using the VIMOS instrument on ESO's Very Large Telescope in Chile and FOCAS on the Subaru Telescope in Hawaii, operated by the National Astronomical Observatory of Japan.

With these observations, the astronomers identified several groups of galaxies surrounding the main galaxy cluster.

The researchers were able to distinguish tens of such clumps, each typically ten times as massive as our own Milky Way galaxy — and some as much as a thousand times more massive — while they estimate that the mass of the cluster amounts to at least ten thousand times the mass of the Milky Way.

Some of the clumps are feeling the fatal gravitational pull of the cluster, and will eventually fall into it, the data suggested.

This information will allow scientists to explore how galaxies were affected by their environment at a time when the universe was much younger.

The filament is located about 6.7 billion light-years away from us and extends over at least 60 million light-years. The newly uncovered structure does probably extend farther, beyond the field probed by the team, and hence future observations have already been planned to obtain a definite measurement of its size.