Physicists propose looking at dark matter not as a single mysterious particle that has been sought for decades, but as an entire hidden world with its own "chemistry." Scientists from NRNU MEPhI and Southern Federal University, along with colleagues from Italy and France, led by Professor Maxim Khlopov, are considering a model of "dark atoms" — structures similar to ordinary atoms, but existing in the invisible sector of the Universe.
The idea arose from an old astrophysical problem: galaxies rotate too quickly. If only stars, gas, and dust were considered, their gravity would not be enough to hold such systems together. This means that alongside visible matter, there must be invisible mass that does not glow but affects the movement of galaxies.
Previously, WIMPs — weakly interacting massive particles — were considered the main candidate for this mass. But neither the Large Hadron Collider nor underground detectors have yet yielded convincing results. Therefore, physicists are increasingly exploring other scenarios: perhaps dark matter is more complex and can assemble into neutral "atoms" from its analogues of electrons, protons, and photons.
In one model, a superheavy particle with a large negative charge can capture helium nuclei. This creates an electrically neutral "dark atom" that hardly interacts with light and behaves like cold invisible matter. According to scientists' calculations, such structures could have formed much more efficiently in the early Universe than previously thought.
This scheme can explain several strange observations at once. The AMS detector on the International Space Station has been recording an excess of positrons — electron antiparticles — for more than ten years. According to the MEPhI model, these can be created by a small remaining charged part of the dark plasma, while neutral "dark atoms" form a large halo around the Galaxy and do not produce excess gamma radiation, which would have appeared in other versions.
Another clue may be found on Earth. The Italian DAMA/LIBRA experiment has observed seasonal bursts in sodium iodide crystals for many years. According to physicists' calculations, heavy "dark atoms" with a mass of up to 11 TeV can pass through the planet, slow down, and bind with sodium nuclei, emitting photons with an energy of 1–6 keV. Such a signal should change once a year, as the Earth moves towards the dark matter stream and then away from it.
Now the authors continue to refine quantum-mechanical models and search for parameters under which "dark atoms" will be consistent with all accumulated data. If the hypothesis is confirmed, the hunt for dark matter may change: instead of searching for a single particle, physicists will have to study an entire hidden "periodic table" of the invisible Universe.
Read more on the topic:
- MEPhI gamma-ray telescope prototype to distinguish dark matter from interference: picosecond protection surpasses American "Fermi"
- Research on Dark Matter, a Key Component of the Universe, Begins at MEPhI
- The Invisible Will Become Visible: The First Dark Matter Search Facility Will Be Created in Russia