We have been searching for dark matter for 90 years. Now a Japanese man believes he has found his “fingerprint”
Since Fritz Zwicky suggested the existence of dark matter in 1933, the reality is that it has been one of the great ghosts of modern physics, generating many debates about its existence. The little we know indicates that this matter is there because we see how its gravity pushes galaxiesbut we have never been able to see it or touch it. It is invisible. Or at least, that’s what we believed until now. And to ‘see’ this matter you have to be a true superhero, since it does not emit, absorb or reflect light. Something that makes it completely invisible to telescopes around the world. But it is not something that is a small part of what surrounds us, but which makes up 85% of the total matter in the universe. But now there is hope to have more information about this great mystery of physics thanks to a study Professor Tomonori Totani of the University of Tokyo claims to have found the first direct evidence of this elusive substance. He has not seen it directly with his own eyes, but he has detected the “smoke” of his gun: a very specific gamma ray signal emanating from the halo of our own Milky Way and that eerily coincides with theoretical predictions of how dark matter behaves. A large amount of data. To understand the discovery, you have to look at the sky with gamma ray eyes. Totani has used a total of 15 years of data accumulated by NASA’s Fermi Gamma-ray Space Telescope (LAT). But the important thing was undoubtedly knowing where to look: in the galactic halo. That is, the ‘quiet’ outskirts of the Milky Way, excluding the galactic disk to avoid interference. What he found when cleaning the background noise was surprising: an excess of gamma rays with a very specific energy peak, located at 20 billion electron volts (20 GeV). The importance. So far so good, but… Why is it important? Basically, because it doesn’t fit what we would expect from normal astrophysical sources, like pulsars or supernova remnants. However, it fits like a glove for the WIMP theory. This is a theory that basically suggests that dark matter It is made up of WIMPs (Weakly Interacting Massive Particles). According to physical models, when two of these particles collide, they annihilate each other, releasing a cascade of energy in the form of gamma rays that would be detected in the universe now. And that is their conclusion: the detected signal is compatible with WIMP particles that have a mass of 500 times that of a proton. This would, therefore, be the fingerprint that gives the most information about dark matter, although it does not stop there. The shape is not a point on the map, but a soft, spherical halo that surrounds the galaxy, just as dark matter is distributed in the cosmological simulations that physics has made. The same goes for consistency, since the signal persists even when different background models are used and other known sources of noise in the universe are removed. There are precedents. This isn’t the first time someone has yelled “Eureka!” In the past, excess gamma rays have been detected at the Galactic Center (known as GCE), but the scientific community has tended to think that this signal comes from undetected millisecond pulsars, rather than dark matter. The key to Totani’s study is that he has looked where no one was looking in such detail. By moving away from the center and analyzing the diffuse halo, it is where he has found a much cleaner signal that does not invite so many doubts about its origin. There are still doubts. The study itself admits that the calculated cross section (the probability of interaction) is higher than the upper levels established by the observation of dwarf galaxies, which are often used as scale for dark matter. This means two things: either our models of the density of dark matter in the Milky Way are incorrect (which is possible, since there is a lot of uncertainty in the profile of the halo), or we are looking at a new and unknown astrophysical phenomenon that mimics dark matter. A great mystery. If this finding is confirmed, we would be facing one of the greatest discoveries in physics of the 21st century. It would confirm that dark matter is composed of particles that we can detect (and not primordial black holes) and open a new door for physics. go beyond the standard model. But as we say, this still needs to be verified by a second laboratory such as the Cherenkov Telescope Array Observatory (CTAO) that may have the ability to detect these gamma ray spectral lines. Image | A. Schaller (STScI) In Xataka | Exactly 100 years ago we began to understand how the world works. Quantum physics has radically changed our lives
