Is the Milky Way’s glow dark matter killing itself?

The galactic center gamma-ray excess recorded by Fermi. (NASA Goddard/A. Mellinger (Central Michigan Univ.) and T. Linden (Univ. of Chicago))

Welcome to FreeAstroScience, dear readers. Here’s a question buzzing through astronomy today: what’s lighting up the Milky Way’s heart—and could it be dark matter particles annihilating each other? In this article, written by FreeAstroScience only for you, we unpack a fresh line of evidence, the alternatives on the table, and how scientists are trying to break the tie. Stick with us to the end: we’ll turn a tricky debate into a clear, engaging story you can share with friends.

What is the Galactic Center GeV Excess—and why is it a big deal?

Since 2009, NASA’s Fermi telescope has seen an extra glow of GeV gamma rays in the direction of the Milky Way’s center. It’s brighter than standard models predict, and it’s stubbornly hard to explain. Two suspects dominate the case file:

• Dark matter annihilation—in particular, hypothetical WIMPs (weakly interacting massive particles) colliding and converting mass to radiation.
• **Millisecond pulsars (MSPs)**—rapidly spinning neutron stars that beam high-energy light. Both naturally make gamma rays. Both plausibly gather in the inner Galaxy. And both can fit parts of the data.

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Dark matter or pulsars—who fits the glow better?

What do the two hypotheses actually predict?

Here’s a compact, scannable comparison.

Feature	Dark matter annihilation	Millisecond pulsars (MSPs)
Physical driver	WIMP–anti-WIMP collisions → particle showers → γ-rays	Spinning neutron stars beaming radiation
Expected morphology	Follows dark-matter halo; often modeled as smooth, roughly spherical	Follows bulge stars; could look “boxy”/X-shaped like the bulge population
Small-scale texture	Smooth glow (diffuse)	“Speckled” pattern from many point sources
How to test	Look for halo-shaped signal, dwarf galaxy counterparts, spectral shape	Resolve individual pulsars; check population counts & luminosities

Observationally, teams have reported both boxy features (which sound pulsar-ish) and a spectrum/magnitude that can be modeled with dark matter parameters. The stalemate has lasted for years.

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What changed in 2025?

Did new simulations just give dark matter a “shape” advantage?

A new study led by Moorits Mihkel Muru used supercomputer simulations of Milky-Way-like galaxies to reevaluate the glow’s morphology. If the dark matter halo were perfectly round, a “boxy” excess would lean toward pulsars. But the simulations suggest our halo is slightly flattened—a natural byproduct of the Milky Way’s merger history. Projected on our sky, that flattening can make a boxy-looking gamma signature even if the source is dark matter annihilation. In other words, shape alone no longer disqualifies dark matter.

The team concludes that both scenarios—dark matter and MSPs—remain equally plausible based on morphology, spectrum, and intensity, with a slight edge for dark matter given a deficit of detected MSPs in the bulge compared with what would be needed. That edge is cautious, not conclusive.

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But what about the “speckles”—don’t they point to pulsars?

Small-scale granularity in the glow, reported in earlier analyses, looks like the fingerprint of many unresolved point sources—exactly what MSPs are. The new work focuses on large-scale shape, not that fine texture. The honest read today is that both processes might contribute: a smooth annihilation background plus a pointy pulsar population on top. That’s not fence-sitting; it’s how complex astrophysical environments usually behave.

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How do scientists compute the gamma-ray signal from dark matter?

Two simple relations carry the intuition.

1) Annihilation rate in a volume

$\Gamma =\frac{1}{2}⟨\sigma v⟩n^2$

• $⟨\sigma v⟩$ is the velocity-averaged annihilation cross-section;
• $n$ is the number density of dark-matter particles.

2) Differential gamma-ray flux along a line of sight

$\frac{d\Phi }{dE}=\frac{⟨}{\sigma }\times \frac{d{N}_{\gamma }}{dE}\times J$

with the J-factor encoding how dark matter piles up along the sightline: $J={\displaystyle \int {\rho }^2\left(l\right)dl}$

These formulas show why morphology matters: ρ² rewards regions where the halo is denser—and any flattening or triaxiality can reshape the sky pattern of the predicted glow. That’s exactly the 2025 simulations’ point.

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What would pulsars need to explain the excess?

MSPs shine in gamma rays with efficiencies that scale with their spin-down power. A simplified budget looks like this:

$L_{\gamma }\approx \eta ·{Ė}_{\mathrm{tot}}$

• $\eta$ is an efficiency factor;
• ${Ė}_{\mathrm{tot}}$ sums the spin-down power across all bulge MSPs.

To match the GCE, you’d need enough bulge pulsars with the right luminosity function. The catch, raised again in 2025, is a shortfall in detected MSPs compared with some model requirements—hence that “slight edge” to dark matter in intensity terms. Ongoing surveys could still close the gap if many are faint or hidden by dust.

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Can upcoming telescopes break the tie?

Yes—by pushing both resolution and energy reach:

• Cherenkov Telescope Array (CTA) will sharpen the gamma-ray view from tens of GeV upward, testing spectra and morphology with new precision.
• Southern Wide-field Gamma-ray Observatory (SWGO) will watch the southern sky for extended, diffuse emission signatures that complement CTA.

Meanwhile, multi-wavelength campaigns—radio (pulsar timing), X-ray (neutron-star populations), infrared (bulge structure)—can triangulate the culprit(s). Think of it as astrophysics’ version of a team-of-detectives case file.

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Why does “boxy vs spherical” keep coming up?

Because stellar bulge maps look boxy/X-shaped, while dark matter halos are often modeled spherical—a clean visual separation. But the 2025 simulations show the halo needn’t be perfectly round. Ancient galaxy mergers can flatten and twist the halo, skewing the projected signal and mimicking bulge-like features. That realization removes a major “quick dismissal” of the dark-matter idea.

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What should we watch for next?

• Point-source counts: deeper radio/X-ray work to tally hidden MSPs in the bulge.
• Spectral shapes: does the GCE spectrum match canonical WIMP masses/channels or known MSP spectra?
• Spatial cross-checks: does the glow trace stars, halo mass, or some hybrid?
• External controls: similar analyses toward dwarf spheroidal galaxies (dark-matter-rich, star-poor) to see if a matched excess appears.

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Mini-timeline: how we got here

Date	Milestone
2009	Fermi data reveal a gamma-ray excess toward the Galactic Center.
2010s	Debate intensifies: dark matter vs. unresolved millisecond pulsars.
Late 2010s–2020s	Hints of “speckling” suggest point sources; morphology studies multiply.
Oct 23, 2025	New simulations show a slightly flattened halo can produce boxy-looking glow, keeping dark matter in play.
Mid-2020s onward	CTA & SWGO poised to test spectra and morphology more sharply.

Key references and context: ScienceAlert coverage and linked research discussions. :contentReference[oaicite:14]{index=14}

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So…are we seeing dark matter destroy itself?

We’re not ready to print the T-shirts. Yet the 2025 work reminds us to respect the Galaxy’s complexity. With a halo that’s not perfectly round, dark matter can still draw the “boxy” outline many thought belonged only to pulsars. At the same time, point-source speckling keeps MSPs squarely in the frame. The most likely near-term answer is both—with upcoming observatories telling us how much of each.

The bigger picture

Dark matter dominates cosmic structure, sculpting galaxies and clusters. If the Milky Way’s heart is whispering its annihilation signature, that would be a profound breakthrough—connecting cosmic architecture to particle physics in one signal. And if pulsars turn out to be the main act, that’s still a victory: we’ll have mapped an ancient stellar population with exquisite detail. Either way, the Universe wins—and so do we.

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The research has been published in Physical Review Letters.