The Cold Spot area resides in the constellation Eridanus in the southern galactic hemisphere. The insets show the environment of this anomalous patch of the sky as mapped by Szapudi's team using PS1 and WISE data and as observed in the cosmic microwave background temperature data taken by the Planck satellite. The angular diameter of the vast supervoid aligned with the Cold Spot, which exceeds 30 degrees, is marked by the white circles.
ESA PLANCK COLLABORATION/GRAPHICS BY GERGŐ KRÁNICZ
At the furthest-most reaches of the observable universe lies one of the most enigmatic mysteries of modern cosmology: the cosmic microwave background (CMB) Cold Spot.
Discovered in 2004, this strange feature etched into the primordial echo of the Big Bang has been the focus of many hypotheses — could it be the presence of another universe? Or is it just instrumental error? Now, astronomers may have acquired strong evidence as to the Cold Spot’s origin and, perhaps unsurprisingly, no multiverse hypothesis is required. But it’s not instrumental error either.
When the Cold Spot was first revealed by NASA’s Wilkinson Microwave Anisotropy Probe (WMAP), astronomers quickly realized that the feature, if real, would be the largest structure ever seen in the cosmos. But with just one space telescope providing the measurements, there was always the concern that something mundane — like instrumental error — could be to blame.
Then the European Planck telescope, that was also launched to measure slight temperature variations in the CMB (known as anisotropies), also saw the Cold Spot. Despite some theories that the feature may actually be an error caused by our statistical analysis methods, it was generally thought that the Cold Spot was real.
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.
As I outlined in a recent DNews video, the multiverse hypothesis is certainly one of the more extreme cosmological ideas out there and other explanations for the Cold Spot exist. And one idea that now appears to have gained some meat is that of the existence of a “supervoid” in the universe between us and the Cold Spot imprint in the CMB.
Through the combination of observational data from Hawaii’s Pan-STARRS1 (PS1) telescope located on Haleakala, Maui, and NASA’s Wide Field Survey Explorer (WISE) satellite, István Szapudi of the Institute for Astronomy at the University of Hawaii at Manoa and his collaborators may have found “the largest individual structure ever identified by humanity” and this structure may be creating the anomalous Cold Spot.
Previous studies have shown that there is little evidence for a very distant structure in the direction of the Cold Spot. But, paridoxically, it is harder to identify large structures that are closer to us than further away. By constructing a 3-D map of galaxies, the researchers discovered a vast region, only 3 billion light-years away (that’s close in the grand cosmological scheme of things), that has a lower density of galaxies than the rest of the known universe. This supervoid is huge, measuring about 1.8 billion light-years wide. This vast supervoid could therefore be the largest structure ever identified by humanity.
So Szapudi’s team may have identified a vast supervoid in space, what’s that got to do with the CMB Cold Spot?
The radiation from the CMB is the most ancient form of radiation known in the universe. Created just after the Big Bang nearly 14 billion years ago, this weak glow has to travel from the most distant edge of our observable universe to be detected by our instrumentation. The medium that this radiation travels through is therefore very important.
As the CMB radiation encountered the supervoid, a region of space with a density much lower than the rest of the universe, the Integrated Sachs-Wolfe (ISW) effect may have altered the characteristics of any radiation traveling through it. As the universe is expanding, the radiation traveling through the supervoid will lose more energy than radiation traveling though ‘normal’ space, creating an anomalously cool imprint in the WMAP and Plank anisotrophy maps. This imprint would manifest itself as a huge Cold Spot.
Published in the journal Monthly Notices of the Royal Astronomical Society today, this research falls short of definitively linking the supervoid with the Cold Spot, but it seems unlikely that this vast supervoid located in the same position in the sky as the CMB Cold Spot is just a coincidence.