Modern cosmology is experiencing a strange situation. We have photographed galaxies located more than 13,000 million light years away, detected fossil radiation from the Big Bang, light emitted when the Universe was just a 380,000-year-old baby. We have telescopes that have allowed us to map an important part of the visible matter in the cosmos and indirectly reconstruct the dark matter network that connects galaxies and galactic clusters. However, amid all these achievements, a huge unknown remains. It is not a galaxy, it is not a black hole or a supercluster. In fact, the reality is that… it is not. It is actually a gigantic region where matter seems to be missing, the supervoid of Eridanus. Its size is… Almost inconceivable, although it is measurable.
The observable diameter of the Universe is about 93 billion light years. This means that the Eridanus supervoid, with its 1.8 billion light years, occupies about 2% of the diameter of the observable Universe. Nothing clear? It is 15,000 times larger than the Milky Way. Doesn’t it say anything? Yes, going on the stingy spectrum, NASA points to our galaxy as home to 100 billion planets, We are talking about a region in which 1,500 billion planets could enter, almost 200,000 for each inhabitant of the planet.
The “problem” with the Eridanus supervoid is that the more they study it, the more questions it raises. The experts from the Institute of Astrophysics of the Canary Islands (IAC) explain one of these unknowns: “such a large region seems very unlikely according to the standard cosmological model. Therefore, the Dark Energy Observatory (DES) team followed the hypothesis that A supervoid could explain, at least in part, why this region is significantly larger and colder than expected. Scientists also believe that this gigantic region could be used as a unique laboratory to learn about elusive dark energy.”
The first clue appeared in a photograph of the Big Bang, long before the vacuum itself was detected. In 2004, astronomers took a detailed look at the Cosmic Microwave Background, the fossil radiation left behind after the Big Bang. That Radiation constitutes the oldest image of the Universe that we can observe. And there something strange appeared, a huge region colder than expected. It is not just nothingness, but a nothingness that is colder than expected.
According to the standard cosmological model, such a large, cold anomaly is highly unlikely. The IAC explains it very clearly. Let’s imagine that the photons from the Big Bang that reach our telescopes are cyclists crossing a hill and the hill is the vacuum of Eridanus. As they “begin the ascent” (read: enter a vacuum) they climb a gravitational slope and lose energy. In a static Universe they would recover it when leaving, when “going down the hill”. But this does not happen here: “During their passage, these photons suffer the effect of dark energy, responsible for cosmic expansion, and lose part of their energy.. “This loss is equivalent to a cooling… However, the observed dimensions of the Eridanus supervoid cannot fully explain the deep temperature depression if the standard dark energy model is assumed in the calculations.”
It’s like finding the main suspect in a police mystery and then discovering that he has a partial alibi: we know he’s connected to the crime, but there are gaps left unexplained. And then we come to the question: What if the problem is dark energy?
The standard cosmological model assumes a certain intensity for dark energy, the mysterious component that makes up approximately 70% of the energy content of the Universe. If dark energy were more intense or behaved in a slightly different way than expected, the effect of the supervacuum on fossil radiation could be much greater.
That is why Eridanus has become a kind of natural laboratory to study one of the greatest enigmas of modern physics. It is not that the void necessarily contradicts our theories, but that could be signaling that we are still missing an important piece of the puzzle.
“Hundreds of other supervoids detected in the most distant Universe have also shown moderate evidence of cold spots larger than expected – concludes Andras Kovacs, DES expert -, but The resolution of this long-standing debate in cosmology will most likely come from a next generation of cosmological studies that will map even larger volumes.”.