http://www.physorg.com/news107109720.html

Astronomers find gaping hole in the Universe

llustration of the effect of intervening matter in the cosmos on the cosmic
microwave background (CMB). On the right, the CMB is released shortly after
the Big Bang, with tiny ripples in temperature due to fluctuations in the
early Universe. As this radiation traverses the Universe, filled with a web
of galaxies, clusters, superclusters and voids, it experiences slight
perturbations. In the direction of the giant newly-discovered void, the WMAP
satellite (top left) sees a cold spot, while the VLA (bottom left) sees
fewer radio galaxies. (Credit: Bill Saxton, NRAO/AUI/NSF, NASA)

University of Minnesota astronomers have found an enormous hole in the
Universe, nearly a billion light-years across, empty of both normal matter
such as stars, galaxies and gas, as well as the mysterious, unseen "dark
matter." While earlier studies have shown holes, or voids, in the
large-scale structure of the Universe, this new discovery dwarfs them all.
"Not only has no one ever found a void this big, but we never even expected
to find one this size," said Lawrence Rudnick of the University of Minnesota
astronomy professor. Rudnick, along with grad student Shea Brown and
associate professor Liliya Williams, also of the University of Minnesota,
reported their findings in a paper accepted for publication in the
Astrophysical Journal.

Astronomers have known for years that, on large scales, the Universe has
voids largely empty of matter. However, most of these voids are much smaller
than the one found by Rudnick and his colleagues. In addition, the number of
discovered voids decreases as the size increases.

"What we've found is not normal, based on either observational studies or on
computer simulations of the large-scale evolution of the Universe," Williams
said.

The astronomers drew their conclusion by studying data from the NRAO VLA Sky
Survey (NVSS), a project that imaged the entire sky visible to the Very
Large Array (VLA) radio telescope, part of the National Science Foundation's
National Radio Astronomy Observatory (NRAO). Their study of the NVSS data
showed a remarkable drop in the number of galaxies in a region of sky in the
constellation Eridanus, southwest of Orion.

"We already knew there was something different about this spot in the sky,"
Rudnick said. The region had been dubbed the "WMAP Cold Spot," because it
stood out in a map of the Cosmic Microwave Background (CMB) radiation made
by the Wilkinson Microwave Anisotopy Probe (WMAP) satellite, launched by
NASA in 2001. The CMB, faint radio waves that are the remnant radiation from
the Big Bang, is the earliest "baby picture" available of the Universe.
Irregularities in the CMB show structures that existed only a few hundred
thousand years after the Big Bang.

The WMAP satellite measured temperature differences in the CMB that are only
millionths of a degree. The cold region in Eridanus was discovered in 2004.

Astronomers wondered if the cold spot was intrinsic to the CMB, and thus
indicated some structure in the very early Universe, or whether it could be
caused by something more nearby through which the CMB had to pass on its way
to Earth. Finding the dearth of galaxies in that region by studying NVSS
data resolved that question.

"Although our surprising results need independent confirmation, the slightly
lower temperature of the CMB in this region appears to be caused by a huge
hole devoid of nearly all matter roughly 6-10 billion light-years from
Earth," Rudnick said.

How does a lack of matter cause a lower temperature in the Big Bang's
remnant radiation as seen from Earth"

The answer lies in dark energy, which became a dominant force in the
Universe very recently, when the Universe was already three-quarters of the
size it is today. Dark energy works opposite gravity and is speeding up the
expansion of the Universe. Thanks to dark energy, CMB photons that pass
through a large void just before arriving at Earth have less energy than
those that pass through an area with a normal distribution of matter in the
last leg of their journey.

In a simple expansion of the universe, without dark energy, photons
approaching a large mass -- such as a supercluster of galaxies -- pick up
energy from its gravity. As they pull away, the gravity saps their energy,
and they wind up with the same energy as when they started.

But photons passing through matter-rich space when dark energy became
dominant don't fall back to their original energy level. Dark energy
counteracts the influence of gravity and so the large masses don't sap as
much energy from the photons as they pull away. Thus, these photons arrive
at Earth with a slightly higher energy, or temperature, than they would in a
dark energy-free Universe.

Conversely, photons passing through a large void experience a loss of
energy. The acceleration of the Universe's expansion, and thus dark energy,
were discovered less than a decade ago. The physical properties of dark
energy are unknown, though it is by far the most abundant form of energy in
the Universe today. Learning its nature is one of the most fundamental
current problems in astrophysics.

Source: University of Minnesota

-- 

Ken

"Buddhism elucidates why we are sentient."
"Buddhism follows thought throughout the Universe."
"Karma means that you don't get away with anything."