In 2004, scientists studying the radiation afterglow, or cosmic microwave background (CMB), left over after the Big Bang, have discovered an unusually large and cold area of space, which they termed the Cold Spot.
Although variation in temperature across the Universe is predicted by its rapid early expansion, this particular Cold Spot, located around 3 billion light years from Earth, is much too massive to be explained by the so-called inflation theory.
Prof Carlos Frenk, a Cosmologist at the University of Durham, said: “The Cold Spot raised a lot of eyebrows. The real question was what was causing it and whether it was a challenge to orthodoxy.”
Now, after more than a decade of competing explanations – most of which called for exotic physics – a team of astronomers led by Dr. István Szapudi of the Institute for Astronomy at the University of Hawaii may have found a much simpler and more elegant solution to this outstanding cosmological problem.
Using optical data from Hawaii’s Pan-STARRS1 (PS1) telescope, located on Haleakala, Maui, and infrared observations from NASA’s Wide Field Survey Explorer (WISE) satellite, Szapudi’s team discovered a vast “hole”, or void, in the cosmos, where matter is found at around 20% lower density than elsewhere in the Universe.
This supervoid is a whopping 1.8 billion light years across and might be key to understanding the origins of the Cold Spot.
Travelling through these low-density patches, radiation loses energy (explained by the accelerated expansion of the Universe), meaning that when light finally exits the void, it does so at a longer wavelength that corresponds to colder temperatures.
Getting through a supervoid takes hundreds of millions of years, even at the speed of light, so this measurable effect, known as the Integrated Sachs-Wolfe (ISW) effect, might provide the first explanation of one of the most significant anomalies found to date in the CMB, first by a NASA satellite called the Wilkinson Microwave Anisotropy Probe (WMAP), and more recently, by Planck, a satellite launched by the European Space Agency.
This is the first time the existence of such a void has been supported by compelling evidence, and even though a supervoid, in and of itself, is not enough to explain the Cold Spot, it is highly unlikely that these two entities formed in the same location by pure accident.
While this is a significant finding, the survey – described in Monthly Notices of the Royal Astronomical Society – also presents researchers with a new conundrum: “It just pushed the explanation one layer deeper,” said Dr Roberto Trotta, a Cosmologist at the Imperial College London. “Now we have to figure out how does the void itself forms. It’s still a rare event.”
The team will continue its work using improved data from PS1 and the Dark Energy Survey, conducted with a telescope in Chile, to further study the Cold Spot and supervoid, as well as another large void located near the constellation Draco.