The largest known structure in the universe
has been discovered by an international team of astronomers. The large
quasar group (LQG -a portion shown above)) is so large that it would
take a vehicle traveling at the speed of light some 4 billion years to
cross it. Quasars are the nuclei of galaxies from the early days of the
universe that undergo brief periods of extremely high brightness that
make them visible across huge distances. These periods are 'brief' in
astrophysics terms but actually last 10-100 million years. Since 1982 it
has been known that quasars tend to group together in clumps or 'structures' of surprisingly large sizes, forming large quasar groups or LQGs.
The LQG also challenges the Cosmological Principle,
the assumption that the universe, when viewed at a sufficiently large
scale, looks the same no matter where you are observing it from. The
modern theory of cosmology is based on the work of Albert Einstein,
and depends on the assumption of the Cosmological Principle. The
Principle is assumed but has never been demonstrated observationally
'beyond reasonable doubt'.
To give some sense of scale, our galaxy, the Milky Way, is separated from its nearest neighbor, the Andromeda Galaxy, by about 0.75 Megaparsecs (Mpc) or 2.5 million light-years.
Whole clusters of galaxies can be 2-3 Mpc across but LQGs can be 200
Mpc or more across. Based on the Cosmological Principle and the modern
theory of cosmology, calculations suggest that astrophysicists should
not be able to find a structure larger than 370 Mpc. Clowes' newly
discovered LQG however has a typical dimension of 500 Mpc. But because
it is elongated, its longest dimension is 1200 Mpc (or 4 billion light
years) - some 1600 times larger than the distance from the Milky Way to
Andromeda.
"While it is difficult to fathom the scale of this LQG, we can say
quite definitely it is the largest structure ever seen in the entire
universe," said Dr Clowes of University of Central Lancashire's Jeremiah Horrocks
Institute. "This is hugely exciting – not least because it runs counter
to our current understanding of the scale of the universe. Even
travelling at the speed of light, it would take 4 billion years to
cross. This is significant not just because of its size but also because
it challenges the Cosmological Principle, which has been widely
accepted since Einstein. Our team has been looking at similar cases
which add further weight to this challenge and we will be continuing to
investigate these fascinating phenomena."
The team publish their results in the journal Monthly Notices of the Royal Astronomical Society.
Image Credit: R. G. Clowes / UCLan
Source: The Daily Galaxy via Royal Astronomical Society
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