For nearly a century, dark matter has posed a significant enigma. Although it outnumbers ordinary matter by a ratio of five to one, it remains invisible and undetectable by current technology.

A daring new analysis of 15 years of data from NASA’s Fermi Gamma-ray Space Telescope now claims to shed light on this mystery.

The latest research reveals the detection of a peculiar halo-like glow of gamma rays surrounding the Milky Way galaxy, with distinct peaks in energy that align closely with the signals predicted for a specific type of hypothetical dark matter particle.

These particles, referred to as weakly interacting massive particles (WIMPs), can generate gamma rays by annihilating one another.

“If this is validated, it would be the first instance where humanity has ‘seen’ dark matter,” stated Professor Tomonori Toya, an astronomer at the University of Tokyo and co-author of the study.

In an interview with BBC Science Focus, he expressed his initial skepticism: “When I first noticed what looked like a traffic light, I was doubtful, but after careful investigation, I became convinced it was accurate—it was an exhilarating moment,” he shared.

However, despite the excitement surrounding the new signals, independent experts caution that this discovery is far from conclusive.

This possible breakthrough emerges nearly a century after Swiss astronomer Fritz Zwicky first proposed dark matter’s existence, after observing that the galaxies in the Milky Way cluster were moving too swiftly for their visible mass.

Mr. Toya’s study, published in the Journal of Cosmology and Astroparticle Physics, scrutinized 15 years of data from the Fermi telescope, focusing on the regions above and below the Milky Way’s main disk—known as the galactic halo.

After modeling and accounting for known sources of gamma rays, such as interstellar gas interactions, cosmic rays, and massive bubbles of high-energy plasma at the galaxy’s center, he identified a leftover component that shouldn’t exist.

“We detected gamma rays with a photon energy measuring 20 giga-electron volts (or an impressive 20 billion electron volts), extending in a halo-like formation toward the Milky Way’s center,” Toya explained. “This gamma-ray-emitting component aligns with the expected shape of a dark matter halo.”

A gigaelectronvolt (GeV) represents a unit of energy utilized by physicists to quantify subatomic particles’ energy levels—approximately a billion times the energy that a single electron attains when traversing a 1-volt battery.

The potential dark matter signal identified by Toya sharply rises from a few GeV, peaks around 20 GeV, and subsequently declines, consistent with predictions for WIMPs, which possess about 500 times the mass of a proton.

In Totani’s perspective, this data significantly indicates the existence of dark matter. “This marks a crucial advancement in astronomy and physics,” he asserts.

Nevertheless, Jan Conrad, a professor of astroparticle physics at Stockholm University in Sweden and an independent expert in gamma-ray searches for dark matter, advises prudence.

“Making claims based on Fermi data is notoriously challenging,” he remarked to BBC Science Focus.

This isn’t the first instance of astronomers witnessing such phenomena; the story stretches back to 2009, shortly after the Fermi telescope’s launch. In that year, researchers identified an unexplained surplus of gamma rays emanating from the galactic center.

For years, this finding stood out as a compelling hint of dark matter. However, Conrad pointed out that even after 16 years, the scientific community has yet to arrive at a consensus about the signal’s dark matter roots.

“It’s believed to be related to dark matter,” he claims. “Despite accumulating data and enhanced methods since then, the question of dark matter’s existence remains unresolved.”

Even at this juncture, researchers who have spent over a decade working to disprove the galactic center excess are unable to definitively prove it is astrophysical in nature (originating from sources other than dark matter), nor can they confirm it is attributable to dark matter. The issue remains unsolved.

Conrad emphasized that the emerging signals from the halo are insufficiently studied and will likely necessitate many more years of investigation for verification. Both the new halo anomaly and the much-debated galactic center signal share a common challenge: noise interference.

In these regions, gamma rays potentially stemming from dark matter annihilation may also originate from numerous other, poorly understood sources—complicating efforts to reach definitive conclusions.

“The uncertainties surrounding astrophysical sources make it exceedingly difficult to assert strong claims,” Conrad stated.

Despite their differing confidence levels, both Totani and Conrad highlight the same forthcoming focus: dwarf galaxies.

These small, faint galaxies orbiting the Milky Way are believed to contain significant amounts of dark matter while exhibiting minimal astrophysical gamma-ray background, rendering them ideal for studying dark matter annihilation.

“If we detect a similar excess in dwarf galaxies, that would provide compelling evidence,” Conrad said. “Dwarf galaxies provide a much cleaner environment, allowing for potential confirmation.”

Dr. Toya concurred, noting, “If the results of this study are validated, it wouldn’t be surprising to observe gamma rays emitting from dwarf galaxies.”

Yet, the ultimate verification of Toya’s discovery might be closer to home. Experiments designed to detect dark matter are currently taking place in facilities situated deep underground around the world.

“If we were to observe a signal there that aligns with a WIMP of the same mass…that would present a robust argument, as it would be much cleaner,” Conrad pointed out.

In the coming years, the next-generation Cherenkov Telescope Array Observatory (CTAO) will significantly enhance sensitivity to high-energy gamma rays, enabling researchers to analyze halo signals with greater detail.

“Naturally, if this turns out to be true, it’s a significant discovery,” Conrad said. “The true nature of dark matter remains elusive. A clear signal indicating dark matter particles would be monumental. However, further research is essential to explore alternative explanations for this excess.”

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