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article imageStrange gigantic supervoid or Cold Spot found in universe

By Stephen Morgan     Apr 21, 2015 in Science
A mysterious "hole in space" called a "supervoid" has baffled scientists since it was first found in 2004. Now a new theory is trying to explain its highly unusual features.
The "hole in space" was first discovered 10 years ago, and is situated in the Eridanus constellation in the southern galactic hemisphere. According to the Guardian,
"Its existence only emerged thanks to a targeted astronomical survey, which confirmed that around 10,000 galaxies were 'missing' from the part of the sky it sits in."
Astronomers were examining radiation left over from the Big Bang, when they discovered a colossal Cold Spot, which is an exceptionally cold area of the cosmos.
Science Daily says that the Big Bang theory does predict warmer and cooler spots of different sizes in the early universe, but scientists had never expected to find a spot, which was so huge and so cold.
What made it difficult to explain was that as a CMB Cold Spot, it exceeded fluctuations in temperature in the CMB predicted by existing physics. The CMB is cosmic microwave background radiation left over from the Big Bang.
It looked like some gigantic supervoid of proportions never before seen by astronomers. Measuring some 1.8 billion light-years across, its size makes it the biggest object ever found in the cosmos.
Dr Istvan Szapudi at the Institute for Astronomy at the University of Hawaii describes as "the largest individual structure ever identified by humanity".
Consequently, various theories have been put forward to try to explain this strange "hole in the universe."
“The Cold Spot raised a lot of eyebrows," said Prof Carlos Frenk, a cosmologist at the University of Durham. "The real question was what was causing it and whether it was a challenge to orthodoxy.”
Some scientists dismissed it as a mistake in calculations made by scientific instruments, while others went so far as to suggest it was a manifestation of large scale quantum entanglement with another universe.
According to them, the supervoid could be a confirmation of superstring theory, which proposes that our universe is just one of many universes or a multiverse.
Discovery News said,
"One of the most extreme (and, frankly, exciting) hypotheses possibly explaining the Cold Spot focused around the multiverse. Stemming from superstring theory, the multiverse posits that our universe is just one of many universes in a bubbly soup of universes (universi?). And that Cold Spot? Well, it could be one of those neighboring universes nuzzling up against our own."
The supervoid is not exactly a total void, but is relatively "empty" compared with the rest of the universe. In fact, it does actually contain galaxies, but far fewer than other regions of space.
“Supervoids are not entirely empty, they’re under-dense,” said András Kovács, a co-author at the Eötvös Loránd University in Budapest.
Wired says that the team used the Hawaii's Pan-STARRS1 (PS1) telescope and Nasa's Wide Field Survey Explorer (WISE) to cover a much wider area of the universe than before. They found that the object was so cold because light which entered it, left it with less energy and at a longer wavelength than before – something called the Integrated Sachs-Wolfe effect.
Science Daily explains,
"Imagine there is a huge void with very little matter between you (the observer) and the CMB. Now think of the void as a hill. As the light enters the void, it must climb this hill. If the universe were not undergoing accelerating expansion, then the void would not evolve significantly, and light would descend the hill and regain the energy it lost as it exits the void. But with the accelerating expansion, the hill is measurably stretched as the light is traveling over it. By the time the light descends the hill, the hill has gotten flatter than when the light entered, so the light cannot pick up all the speed it lost upon entering the void. The light exits the void with less energy, and therefore at a longer wavelength, which corresponds to a colder temperature."
This would mean that there would be a CMB Cold Spot and a supervoid at the same location and that suggest that the supervoid is, in fact, a Cold Spot. It would also reinforce the idea that the universe is expanding and that is linked to the effect of dark matter.
Therefore, Frenks says, “This is independent evidence, in case anyone doubts it, for the existence of dark energy.”
Map of dark matter (light blue)  digitally superposed on a photograph made by the Hubble Space Teles...
Map of dark matter (light blue), digitally superposed on a photograph made by the Hubble Space Telescope, shows that a giant ring of invisible mass surrounds the dense core of a giant cluster of galaxies called ZwC10024+1652,
NASA, ESA, M.J.Jee and H. Ford (Johns Hopkins University)
However, the theory is far from conclusive, and the study itself calls the explanation as only a "plausible cause." Indeed, as the Guardian mentions, it may instead serve to deepen the mystery even further.
“It just pushed the explanation one layer deeper,” said Dr Roberto Trotta, a cosmologist at Imperial College London. “Now we have to figure out how does the void itself form. It’s still a rare event.”
Even more puzzling says the Guardian, is that the supervoid can only account for about 10% of the Cold Spot’s temperature dip according to Frenk from Durham University.
“The void itself I’m not so unhappy about," he says. "It’s like the Everest of voids – there has to be one that’s bigger than the rest,” he said. “But it doesn’t explain the whole Cold Spot, which we’re still in the dark about.”
The team has published its findings in the journal Monthly Notices of the Royal Astronomical Society.
More about supervoid, cold spot, Universe, Biggest, Largest
 
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