An international team of astronomers led by Dr Istvan Szapudi of the University of Hawaii’s Institute for Astronomy has discovered a large supervoid – a vast region roughly 1.8 billion light-years across in which the density of galaxies is much lower than usual in the known Universe – in the direction of an unusually cold area of the sky known as the Cold Spot.

Map of the cosmic microwave background; the insets show the environment of the Cold Spot. The angular diameter of the vast supervoid aligned with the Cold Spot, which exceeds 30 degrees, is marked by the white circles. Image credit: ESA Planck Collaboration / Gergö Kránicz.

Map of the cosmic microwave background; the insets show the environment of the Cold Spot. The angular diameter of the vast supervoid aligned with the Cold Spot, which exceeds 30 degrees, is marked by the white circles. Image credit: ESA Planck Collaboration / Gergö Kránicz.

The Cold Spot was discovered in 2004 by scientists examining a map of the cosmic microwave background (CMB). The physics surrounding the Big Bang theory predicts warmer and cooler spots of various sizes in the infant Universe, but a spot this large and this cold was unexpected.

Now, Dr Istvan Szapudi and his colleagues from the United States, Hungary, Spain, Italy, and the UK, may have found an explanation for the existence of the Cold Spot, which they say may be the largest individual structure ever found.

“If the Cold Spot originated from the Big Bang itself, it could be a rare sign of exotic physics that the standard cosmology does not explain,” the scientists said.

“If, however, it is caused by a foreground structure between Earth and the CMB, it would be a sign that there is an extremely rare large-scale structure in the mass distribution of the Universe.”

Using data collected by NASA’s Wide Field Survey Explorer satellite and the ground-based Pan-STARRS1 telescope, the astronomers detected an enormous ‘hole,’ or supervoid, aligned with the Cold Spot.

The supervoid lies in the constellation Eridanus, approximately 3 billion light-years away from Earth.

“Getting through a supervoid can take millions of years, even at the speed of light, so this measurable effect, known as the Integrated Sachs-Wolfe effect, might provide the first explanation one of the most significant anomalies found to date in the CMB, first by NASA’s Wilkinson Microwave Anisotropy Probe, and more recently, by ESA’s Planck satellite,” said the scientists, who report their discovery in the Monthly Notices of the Royal Astronomical Society.

“While the existence of the supervoid and its expected effect on the CMB do not fully explain the Cold Spot, it is very unlikely that the supervoid and the Cold Spot at the same location are a coincidence.”

Dr Istvan Szapudi and co-authors plan to continue their work using new data from Pan-STARRS1 telescope and from the Dark Energy Survey being conducted with a ground-based telescope to study the Cold Spot and supervoid, as well as another large void located near the constellation Draco.

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István Szapudi et al. 2015. Detection of a supervoid aligned with the cold spot of the cosmic microwave background. MNRAS 450 (1): 288-294; doi: 10.1093/mnras/stv488

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