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.
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.
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