Strange cosmic phenomenon at center of our galaxy points to new kind of dark matter

For decades, scientists have been chasing one of the universe’s greatest mysteries: dark matter. Thought to make up about 85% of all matter, it remains undetected except through its gravitational effects. Now, a puzzling energy phenomenon in the heart of the Milky Way may point to a new form of this elusive substance.

At the core of the Milky Way lies the Central Molecular Zone (CMZ), a dense and chaotic region filled with gas clouds and cosmic radiation. For years, scientists have observed unexpectedly high levels of ionization in the hydrogen gas there—an indication that something is knocking electrons free at an unusual rate. Traditional explanations, like cosmic rays, fail to fully account for the energy required.

Dr. Shyam Balaji, a postdoctoral researcher at King’s College London, describes the mystery: “At the center of our galaxy sit huge clouds of positively charged hydrogen, a mystery to scientists for decades because normally the gas is neutral. So, what is supplying enough energy to knock the negatively charged electrons out of them?”

The latest study, published in Physical Review Letters, suggests an answer that challenges long-standing assumptions about dark matter.

Researchers believe a much lighter form of dark matter—different from the widely studied Weakly Interacting Massive Particles (WIMPs)—could be responsible. Unlike WIMPs, which interact weakly with normal matter, these low-mass dark matter particles might be colliding with each other and producing charged particles that ionize the hydrogen gas.

Most dark matter studies focus on WIMPs, which are thought to pass through normal matter almost undetectably. But this new research suggests that dark matter could be significantly lighter than previously assumed, with masses below 100 MeV. If these particles exist, they could annihilate when they meet, producing electron-positron pairs. These charged particles would then interact with the surrounding molecular gas, causing the observed ionization.

“The data is telling us that dark matter could potentially be a lot lighter than we thought,” Dr. Balaji explains. “By using gas at the CMZ for a different kind of observation, we can get straight to the source.”

This approach offers a fresh perspective on dark matter detection. Rather than relying on Earth-based detectors, which wait for dark matter to interact with visible matter, this method observes how dark matter might actively influence its cosmic surroundings.

Another long-standing cosmic puzzle may be linked to this phenomenon: the mysterious 511-keV emission line from the center of the Milky Way. This energy signature results from the annihilation of positrons, the antimatter counterparts of electrons. For years, scientists have debated what could be producing so many positrons in the galactic core.

If the newly proposed low-mass dark matter particles are responsible for the unusual hydrogen ionization in the CMZ, they could also be generating the positrons that lead to the 511-keV emission line. Once created, these positrons would form positronium—an exotic atom-like state of an electron and a positron—which then decays, emitting gamma rays at precisely 511 keV.

These findings suggest a fresh direction in the search for dark matter, one that focuses on sub-GeV particles rather than the more traditional WIMP models. The study also emphasizes the need to rethink how dark matter experiments are conducted. Instead of relying solely on laboratory-based searches, researchers are now looking to cosmic observations to uncover clues about dark matter’s true nature.

“The search for dark matter is one of fundamental science’s most important objectives,” Dr. Balaji says. “By peering into the center of our Milky Way, the hydrogen gas in the CMZ is suggesting that we may be closer to identifying evidence on the possible nature of dark matter.”

If these results hold up under further scrutiny, they could redefine dark matter research and lead to new experiments designed to test these ideas. Scientists will continue analyzing data from space-based and ground-based observatories to refine their understanding of what’s happening at the galactic center.

The mystery of dark matter remains unsolved, but with each new discovery, researchers move closer to revealing its true identity. The next breakthrough may come not from deep underground detectors, but from the very heart of our own galaxy.

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