Great Cold Spot Points to Largest Void in the Universe

The Cosmic Microwave Background Radiation (CMBR) started out as static in a communications lab in New Jersey where it was discovered by Penzias and Wilson in 1964.  Since then it has proven to be an extremely powerful tool for determining the structure and age of the Universe.  It helps us constrain cosmological models, gives us insight into the inflationary period of the Universe, and tells us where to look for the largest and smallest structures of the Universe.

CMBR from the Planck satellite showing temperature variations of one part in 100,000. Credit: Graphics by Gerg Kránicz. Image credit: ESA Planck Collaboration

The temperature fluctuations seen in the CMBR are so small they can only be quantified in millionths of a degree.  Yet these tiny temperature differences, starting from 300,000 years after the big bang, followed the expansion of the Universe and mapped the future density of galaxies and clusters.  The warmest spots correspond to the largest galaxy clusters of today, while the coolest areas are the great empty voids of the cosmic web.

In 2004, a massive cold spot, some 30 degrees across on the sky, was seen by astronomers.  This cold area was much larger than anything we expected.  It could be related to the Big Bang itself, giving insights into the strange laws of physics that were present in the beginning.  It could also be due to a rare, large-scale structure in the universe lying between us and the CMBR.

Recently, a team of astronomers led by Dr István Szapudi of the Institute for Astronomy at the University of Hawaii at Manoa has found an explanation, which Szapudi characterizes as “the largest individual structure ever identified by humanity.”

By looking at optical and infrared data to characterize the positions and distances of galaxies in the region, the astronomers discovered a 1.8 Billion light-year wide void, where the density of galaxies is much lower than what is typically seen in the universe.  The supervoid is only 3 Billion light-years from Earth, a relatively small distance for a structure of such immense size.

The existence of the supervoid and its effect on the CMBR are not enough to explain the size and temperature of the cold spot, but it is clear that the void and cold spot are not coincidentally found in the same place.  Further study of the region will give new insight into the origins of the great cold spot of the CMBR, and help us further characterize the massive, lonely void in the distant universe.

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