Dark matter may reveal itself in a faint glow around the Milky Way

In the early 1930s, Swiss astronomer Fritz Zwicky noticed that galaxies in clusters were flying around too fast to be held together by the gravity of their visible stars alone. He proposed an unseen framework – dark matter – doing the heavy lifting. 

Nearly 100 years later, a new analysis of NASA’s Fermi Gamma-ray Space Telescope data claims to spot the kind of high energy light that theorists have long said dark matter might produce.

This signal could potentially let us “see” the invisible for the first time.

Why dark matter hides

Dark matter doesn’t interact with electromagnetic forces, so it doesn’t emit, reflect, or absorb light. That makes telescopes blind to it, except indirectly, through gravity. 

One popular idea is that dark matter could be made of weakly interacting massive particles (WIMPs). They would be far heavier than protons and interact only feebly with normal matter. 

However, when two WIMPs meet, they could annihilate and spit out standard particles, including gamma-ray photons.

If that happens, the densest dark matter real estate, such as the Milky Way’s central halo, should glow faintly in gamma rays with a characteristic energy pattern.

A halo-shaped glow

Using the latest Fermi observations, Tomonori Totani of the University of Tokyo reports such a pattern toward the Galactic center. 

“We detected gamma rays with a photon energy of 20 gigaelectronvolts (or 20 billion electronvolts, an extremely large amount of energy) extending in a halolike structure toward the center of the Milky Way galaxy,” said Totani.

“The gamma-ray emission component closely matches the shape expected from the dark matter halo.”

Signals that align with dark matter

In his analysis, the energy spectrum – the way the signal’s brightness changes with energy – lines up with expectations for annihilating WIMPs of roughly 500 proton masses.

Just as crucial, the inferred rate of annihilation sits comfortably within the ranges theorists have considered plausible. 

According to Totani, conventional culprits (like pulsars or cosmic-ray interactions) struggle to reproduce the halo-shaped, 20-GeV-peaked signal he extracts.

Profound implications of the research

“If this is correct, to the extent of my knowledge, it would mark the first time humanity has ‘seen’ dark matter,” said Totani.

“And it turns out that dark matter is a new particle not included in the current standard model of particle physics. This signifies a major development in astronomy and physics.” 

A detection at these energies would point squarely to physics beyond the Standard Model and add a long-missing particle clue to the cosmological picture drawn from gravity alone.

How the discovery may be confirmed

Extraordinary claims need independent checks. Totani’s map shows a broad, halo-like excess after subtracting other gamma-ray components, but the Milky Way’s center is a messy, luminous place. 

Other teams will need to reproduce the signal with different cleaning methods and modeling assumptions.

The strongest corroboration would be a matching glow in quieter, dark matter-dominated targets. Nearby dwarf spheroidal galaxies embedded in the Milky Way’s halo are prime candidates. 

“This may be achieved once more data is accumulated, and if so, it would provide even stronger evidence that the gamma rays originate from dark matter,” Totani said.

Complementary searches matter, too. Direct detection experiments buried deep underground continue to listen for the rare taps of WIMPs on atomic nuclei, while the Large Hadron Collider and future colliders hunt for missing energy signatures that could betray new particles. 

A consistent mass scale emerging across these approaches would transform a tantalizing hint into a coherent discovery narrative.

Why the signal stands out

For more than a decade, researchers have combed Fermi data for “excesses” around the Galactic center.

Many fizzled as analyses improved, or they were reinterpreted as emission from millisecond pulsars or cosmic-ray electrons. 

Totani’s claim stands out for two major reasons. First, the spatial pattern of the signal resembles the rounded shape of a dark matter halo rather than the disk-like structure of ordinary matter in the Milky Way.

Second, the gamma-ray spectrum peaks near 20 GeV, a sweet spot that several dark matter annihilation models naturally predict.

Totani also reports that the estimated annihilation cross-section implied by the brightness is in the ballpark of “thermal relic” values often cited in WIMP theory, avoiding the need for exotic fine-tuning.

Strengthening the case

Whether this is the long-sought first light from dark matter or a clever phantom conjured by astrophysical complexity will be decided by replication and by tests in cleaner systems. 

Fermi continues to collect photons. Upcoming gamma-ray missions and improved analyses will sharpen the view.

If the same 20-GeV signature pops up in multiple dark matter strongholds, the case strengthens dramatically.

For now, the claim is both bold and measured: a halo-shaped, 20-GeV glow that looks like annihilating WIMPs and resists obvious astrophysical explanations. If follow-up work confirms it, Zwicky’s invisible scaffolding may finally have revealed itself.

The study is published in the Journal of Cosmology and Astroparticle Physics. 

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