More than a decade ago, scientists studying the radiation afterglow of the Big Bang, or cosmic microwave background, noticed something bizarre in their map: an unusually large and cold region of the sky, located in the constellation Eridanus. Although warmer and cooler areas of the young universe have been predicted to exist due to its early and rapid expansion, this particular “Cold Spot” stood out because it is so large that it cannot be explained by this so-called inflation theory. In fact, scientists believe that this could be the largest individual structure to have ever been identified.
This prompted scientists to propose several different hypotheses for its existence, including a type of cosmic defect known as a “texture,” or even a collision with another universe. But scientists were struggling with the fact that many of their ideas required exotic physics, so the origins of this curious Cold Spot remained elusive. Now, it turns out that the explanation may be much simpler than originally believed, as scientists have gathered evidence to suggest that a rare and massive structure located between us and the cosmic microwave background (CMB) may be to blame.
Using optical data from Hawaii’s Pan-STARRS1 (PS1) telescope and infrared observations from NASA’s Wide Field Survey Explorer (WISE) satellite, scientists from the University of Hawaii at Manoa estimated the positions of galaxies in the direction of the Cold Spot. After creating 3D maps of the sky, the scientists observed a monstrous “hole,” or void, in the cosmos. This so-called “supervoid,” in which galaxies and matter are found at significantly lower densities than the rest of the universe, is a whopping 1.8 billion light-years across, and is located around 3 billion light-years away.
Radiation loses energy as it enters and crosses these low-density patches, meaning that when light finally exits the void, it does so at a longer wavelength, which corresponds to a colder temperature. It can take millions of years for radiation to get across these empty areas, so according to the researchers, the measurable effect that they are observing could offer the first explanation for one of the most significant anomalous features of the CMB discovered so far.
As pointed out by New Scientist, although this isn’t the first time that such a void has been proposed, previous studies that claimed to have discovered them have been disputed. And while a supervoid cannot solely explain the Cold Spot, the likelihood that their presence in the same location is merely coincidental is small. The scientists plan to continue their work using improved PS1 data, and also would like to include observations of another large void located near the constellation Draco.