The circled area is the cold spot. Black lines in the Planck‘s CMB map indicates each constellation, cold spot is in Eridanus constellation. The blue circle is the equatorial line in the celestial sphere. Image generated with Celestia.
Scientists may have an explanation for the existence of a particularly cool region in the afterglow of the Big Bang, also known as the cosmic microwave background (CMB).
The origin of this Cold Spot has been a mystery until now, but it could be attributed to the largest absence of galaxies ever discovered.
The scientists used data collected by the Dark Energy Survey (DES) about the Eridanus supervoid. This gap in the cosmic web, once hypothesized but now confirmed, could be a possible cause of the CMB anomaly.
The cosmic web is made up of clusters and superclusters of galaxies. They are attracted by the attractive force of gravity and are accelerated away from each other by the repulsive force of a mysterious phenomenon, not yet understood, called dark energy.
Between these galaxy clusters are voids: vast regions of space that contain fewer galaxies and thus less ordinary matter and less dark matter than exists within galaxy clusters.
Among the largest known structures, the supervoid in the constellation Eridanus is a massive, elongated, cigar-shaped void in the cosmic web that is 1.8 billion light-years across and has been observed to contain about 30% less than matter than the surrounding galactic region. Its center is located 2 billion light-years from Earth, making it the dominant sub-density of matter in our galactic neighborhood.
To make this discovery, scientists used data from the Dark Energy Survey to create a map of dark matter in the same direction as the CMB Cold Spot, looking at the effect of gravitational lensing. It is a phenomenon that occurs when the paths of light are deformed by the gravitational influence of dark matter.
“This dark matter map is the largest map ever created,” Niall Jeffrey, the scientist who worked on building a dark matter map, said in a statement. “We have been able to map dark matter in more than a quarter of the southern hemisphere.”
Scientists previously counted the number of galaxies visible at the location of the Cold Spot and found a low density of galaxies in that region. The new map shows that there is a corresponding subdensity of invisible dark matter.
It’s a new enough element in the long history of the Cold Spot problem that, after this, people will at least be sure there is a supervoid.
The Dark Energy Survey is an international effort to understand the effect dark energy has on the acceleration of the universe. 300 scientists from 25 institutions in seven countries participate in it. He documents hundreds of millions of galaxies, supernovae, and patterns within the cosmic web, using a 570-megapixel digital camera, called DECam, high in the Chilean Andes.
Although the new result confirms that the Eridanus supervoid is gigantic, it is still not enough to explain the discrepancy between the predictions of the current standard cosmological model used to predict the behavior of dark energy, known as the Lambda Cold Dark Matter model, and the observed change in temperature at the Cold Spot that can be attributed to the effect of the supervacuum on CMB photons.