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Observations of the Fermi bubbles and the Galactic center excess with the DArk Matter Particle Explorer

Using 102 months of data from the DArk Matter Particle Explorer (DAMPE), researchers achieved the first independent detection of the Fermi bubbles at $\sim 26\sigma$ significance and a Galactic center GeV excess at $\sim 7\sigma$ , with the latter's spectrum and morphology consistent with dark matter annihilation into $b\bar{b}$ pairs with a mass of $\sim 50$ GeV.

Original authors: F. Alemanno, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, H. Boutin, I. Cagnoli, M. S. Cai, E. Casilli, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, Z. X. Chen, P. Coppin, M. Y. Cu

Published 2026-03-31

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CC BY 4.0

Original authors: F. Alemanno, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, H. Boutin, I. Cagnoli, M. S. Cai, E. Casilli, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, Z. X. Chen, P. Coppin, M. Y. Cui, T. S. Cui, I. De Mitri, F. de Palma, A. Di Giovanni, T. K. Dong, Z. X. Dong, G. Donvito, J. L. Duan, K. K. Duan, R. R. Fan, Y. Z. Fan, F. Fang, K. Fang, C. Q. Feng, L. Feng, S. Fogliacco, J. M. Frieden, P. Fusco, M. Gao, F. Gargano, E. Ghose, K. Gong, Y. Z. Gong, D. Y. Guo, J. H. Guo, S. X. Han, Y. M. Hu, G. S. Huang, X. Y. Huang, Y. Y. Huang, M. Ionica, L. Y. Jiang, W. Jiang, Y. Z. Jiang, J. Kong, A. Kotenko, D. Kyratzis, S. J. Lei, B. Li, M. B. Li, W. H. Li, W. L. Li, X. Li, X. Q. Li, Y. M. Liang, C. M. Liu, H. Liu, J. Liu, S. B. Liu, Y. Liu, F. Loparco, M. Ma, P. X. Ma, T. Ma, X. Y. Ma, G. Marsella, M. N. Mazziotta, D. Mo, Y. Nie, X. Y. Niu, A. Parenti, W. X. Peng, X. Y. Peng, C. Perrina, E. Putti-Garcia, R. Qiao, J. N. Rao, Y. Rong, R. Sarkar, P. Savina, A. Serpolla, Z. Shangguan, W. H. Shen, Z. Q. Shen, Z. T. Shen, L. Silveri, J. X. Song, H. Su, M. Su, H. R. Sun, Z. Y. Sun, A. Surdo, X. J. Teng, A. Tykhonov, G. F. Wang, J. Z. Wang, L. G. Wang, S. Wang, X. L. Wang, Y. F. Wang, D. M. Wei, J. J. Wei, Y. F. Wei, D. Wu, J. Wu, S. S. Wu, X. Wu, Z. Q. Xia, Z. Xiong, E. H. Xu, H. T. Xu, J. Xu, Z. H. Xu, Z. L. Xu, Z. Z. Xu, G. F. Xue, M. Y. Yan, H. B. Yang, P. Yang, Y. Q. Yang, H. J. Yao, Y. H. Yu, Q. Yuan, C. Yue, J. J. Zang, S. X. Zhang, W. Z. Zhang, Yan Zhang, Yi Zhang, Y. J. Zhang, Y. L. Zhang, Y. P. Zhang, Y. Q. Zhang, Z. Zhang, Z. Y. Zhang, C. Zhao, H. Y. Zhao, X. F. Zhao, C. Y. Zhou, X. Zhu, Y. Zhu

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the Milky Way galaxy as a giant, bustling city. At the very center of this city lies the Galactic Center, a chaotic downtown area packed with a supermassive black hole, dense star clusters, and a mysterious, invisible substance called Dark Matter.

For years, astronomers have been looking at this "downtown" through a specific pair of glasses: the Fermi-LAT telescope. They saw two strange, glowing phenomena that didn't quite fit the standard city map:

The Fermi Bubbles: Two giant, balloon-like structures of high-energy light stretching far above and below the city center, like massive bubbles rising from a soda can.
The Galactic Center Excess: A fuzzy, bright glow right in the middle of the city that seemed too intense to be explained by known stars or gas.

Now, a new pair of glasses has arrived on the scene: the DAMPE (DArk Matter Particle Explorer) satellite. Launched by China in 2015, DAMPE is like a high-definition, ultra-sensitive camera that sees the universe in a different way than Fermi.

This paper is the report card from DAMPE after it spent 8.5 years (from 2016 to 2024) staring at the Galactic Center. Here is what they found, translated into everyday language:

1. The "Second Opinion" Confirmation

Think of the Fermi-LAT telescope as a doctor who diagnosed a patient with a rare condition. Usually, you want a second doctor to confirm the diagnosis before you start treatment.

DAMPE is that second doctor. Using its own unique data and different technology, DAMPE looked at the same "patient" (the Galactic Center) and said: "Yes, we see it too."

They confirmed the Fermi Bubbles are real with an incredibly high level of certainty (26 sigma—imagine flipping a coin and getting heads 26 times in a a row by pure chance; that's how unlikely it is that this is a mistake).
They confirmed the Galactic Center Excess is also real (7 sigma certainty).

This is a big deal because it proves these aren't just glitches or errors in the first telescope's data. They are real features of our universe.

2. The Mystery of the "Ghostly Glow" (Dark Matter?)

The most exciting part of the paper is about the Galactic Center Excess. Why is there so much extra light in the center?

The "Star" Theory: Maybe it's just a swarm of thousands of tiny, dead stars (pulsars) that are too small to see individually, but their combined light creates a glow.
The "Ghost" Theory: Maybe it's Dark Matter. Dark matter is the invisible stuff that holds galaxies together. If dark matter particles crash into each other, they might annihilate and explode into a flash of light (gamma rays).

What did DAMPE find?
DAMPE measured the "color" (energy spectrum) of this glow. It looked like a peak around a specific energy level. When they compared this to a recipe for dark matter collisions, it was a perfect match!

The Recipe: If dark matter particles have a mass of about 50 times the weight of a proton (roughly 50 GeV) and they collide at a specific speed, they would produce exactly the kind of light DAMPE saw.
The Verdict: While they can't say "It IS dark matter" with 100% certainty (because the "swarm of dead stars" theory is still possible), the evidence strongly points to the Dark Matter explanation. It's like finding a fingerprint at a crime scene that matches the suspect perfectly.

3. The "Bubbles" are Sharp and Uniform

Regarding the Fermi Bubbles, DAMPE acted like a forensic artist. They mapped the edges of these giant bubbles.

They found the edges are surprisingly sharp, like a cookie cutter, rather than fuzzy and fading out.
The inside of the bubbles is uniform, like a smooth, flat sheet of light.
This suggests the bubbles were likely created by a sudden, powerful event in the past—perhaps a massive burst of energy from the black hole at the center, like a giant burp or a jet of energy shooting out, rather than a slow, steady leak.

4. Why This Matters

Imagine you are trying to solve a puzzle. You have one picture (Fermi-LAT) that shows the pieces fit together in a certain way. Now you have a second, independent picture (DAMPE) taken from a different angle with a different lens.

If the second picture matches the first, you know the puzzle is real.

Independence: Before this, only Fermi-LAT had seen these things. Now, DAMPE has independently verified them.
Precision: DAMPE has better resolution (sharper vision) for high-energy particles. This helps rule out errors and confirms that the "Dark Matter" explanation for the central glow is a very strong candidate.

The Bottom Line

This paper is a major milestone. It tells us that the strange, glowing structures at the center of our galaxy are real, not optical illusions. Furthermore, the "ghostly glow" in the center looks suspiciously like the signature of Dark Matter particles destroying each other.

While we haven't caught the "ghost" yet, DAMPE has provided the strongest independent evidence to date that we are looking at the right place and the right phenomenon. It's a huge step forward in understanding what the invisible universe is made of.

1. Problem Statement

The Galactic Center (GC) is a region of extreme high-energy astrophysics, hosting a supermassive black hole, dense star clusters, and a peak in dark matter (DM) density. Two prominent diffuse gamma-ray features have been identified by the Fermi Large Area Telescope (Fermi-LAT):

The Fermi Bubbles: Two large, symmetric lobes extending $\sim55^\circ$ above and below the Galactic plane, with a hard spectrum up to $\sim100$ GeV.
The Galactic Center Excess (GCE): An extended, roughly spherical gamma-ray excess centered on the GC, peaking at $\sim1-3$ GeV.

While Fermi-LAT has extensively characterized these sources, the origin of the GCE remains debated, with leading hypotheses including DM annihilation (specifically $\chi\chi \to b\bar{b}$ ) or a population of unresolved millisecond pulsars (MSPs). The Fermi Bubbles' origin (jet activity, accretion winds, or star-driven outflows) is also under investigation.

The Challenge: Independent verification of these sources using a different instrument is crucial to rule out systematic errors specific to Fermi-LAT. Furthermore, the Dark Matter Particle Explorer (DAMPE) offers superior energy resolution and potentially lower cosmic-ray background, providing an opportunity to constrain the spectral and morphological properties of these sources with higher precision.

2. Methodology

The authors analyzed 102 months of DAMPE photon data collected from January 2016 to June 2024 (above 2 GeV).

Data Selection & Processing:
- Used the updated v6.0.3 photon dataset, which reduces proton and electron contamination by $\sim50\%$ and $\sim15\%$ respectively, with only a $\sim3\%$ loss in acceptance.
- Selected High-Energy-Trigger (HET) events, excluding data collected in the South Atlantic Anomaly (SAA) or during solar flares.
- Defined two Regions of Interest (ROIs):
  - Fermi Bubbles: $120^\circ \times 120^\circ$ centered on the GC, excluding $|b| < 5^\circ$ .
  - GC Excess: $40^\circ \times 40^\circ$ centered on the GC, excluding $|b| < 1^\circ$ .
- Applied point-source masks based on the DAMPE 8.7-year catalog (and Fermi-LAT catalog for weak sources).
Analysis Framework:
- Binned Likelihood Analysis: Performed using the DmpST toolkit. The total intensity model $I_{tot}$ is a linear combination of templates scaled by energy-dependent factors.
- Baseline Model Components:
  - Galactic Diffuse Emission (GDE): Modeled using GALPROP with the SLZ10T150 parameter set (pulsar-traced CR sources, $z_h=10$ kpc, $T_S=150$ K).
  - Loop I: Geometric template of two spherical shells.
  - Isotropic Background: Power-law spectrum.
  - Point Sources: Fixed or fitted based on catalog significance.
- Template Construction:
  - Fermi Bubbles: A new flat template was derived from DAMPE residual maps, defined by two polygons to match the significance excess ( $>2\sigma_{bg}$ ).
  - GC Excess: Tested against a generalized Navarro–Frenk–White (gNFW) DM annihilation template ( $J$ -factor map) and various bulge/MSP templates (X-shaped, boxy).
Systematic Uncertainty Evaluation:
- Tested alternative GDE models (e.g., SNR-traced, different halo heights, Fermi-LAT IEM models).
- Varied Fermi Bubble templates (extrapolated vs. Fermi-LAT derived).
- Tested different masking strategies and source catalogs.

3. Key Contributions

First Independent Detection: This paper provides the first independent confirmation of both the Fermi Bubbles and the GCE using a space-borne detector other than Fermi-LAT.
High-Precision Spectral Constraints: Leveraged DAMPE's superior energy resolution to measure the spectral energy distribution (SED) of the bubbles and GCE with reduced systematic uncertainties compared to previous studies.
Morphological Analysis: Detailed morphological study of the GCE, testing the preference for a DM-like spherical profile versus MSP-like bulge profiles.
Dark Matter Parameter Constraints: Derived constraints on DM particle mass and annihilation cross-sections specifically for the DAMPE dataset.

4. Key Results

A. Fermi Bubbles

Significance: Detected with a significance of $\sim26\sigma$ .
Morphology: The derived template shows sharp edges and uniform flux, consistent with previous Fermi-LAT findings. The northern lobe is less significant ( $14\sigma$ ) than the southern lobe ( $22\sigma$ ) due to higher background in the northern sky.
Spectrum:
- Exhibits a hard spectrum with an exponential cutoff.
- Best-fit spectral index: $\Gamma_1 = -1.99 \pm 0.06 (\text{stat}) \pm 0.10 (\text{syst})$ .
- Cutoff energy: $E_{cut} = 204^{+120}_{-60} (\text{stat}) ^{+63}_{-48} (\text{syst})$ GeV.
- The spectrum is consistent with Fermi-LAT results, showing a curvature at $\sim3\sigma$ significance.

B. Galactic Center Excess (GCE)

Significance: Detected with a significance of $\sim7\sigma$ (TS = 80.1) in the 2–200 GeV range.
Morphology:
- The excess is well-described by a gNFW profile with an inner slope $\gamma = 1.23 \pm 0.08$ .
- The shape is consistent with spherical symmetry ( $\epsilon \approx 1.0$ ), slightly favoring the DM hypothesis over the elongated bulge/MSP templates.
- The center is slightly offset ( $\sim0.1^\circ$ ) to the southwest of the dynamic GC, consistent with Fermi-LAT observations but not statistically significant in this dataset.
Spectrum:
- Peaks at $\sim1-3$ GeV with a high-energy tail.
- The SED is consistent with Fermi-LAT measurements, though a slight tension exists in the 8–20 GeV range (DAMPE upper limits are slightly lower).
Systematics: The detection is robust against variations in the GDE model, masking, and source catalogs. The lowest significance found was $6.0\sigma$ (using the XLIX GDE model).

C. Dark Matter Interpretation

Assuming the GCE originates from DM annihilation:

Channel $\chi\chi \to b\bar{b}$ :
- Mass: $m_\chi \approx 49^{+16}_{-12}$ GeV.
- Cross-section: $\langle\sigma v\rangle \approx 1.9^{+0.4}_{-0.3} \times 10^{-26}$ cm $^3$ s $^{-1}$ .
Channel $\chi\chi \to \tau^+\tau^-$ :
- Mass: $m_\chi \approx 13.0^{+1.9}_{-1.8}$ GeV.
- Cross-section: $\langle\sigma v\rangle \approx (6.0 \pm 0.9) \times 10^{-27}$ cm $^3$ s $^{-1}$ .
These parameters are consistent with Fermi-LAT results but are partially in tension with constraints from dwarf spheroidal galaxies (dSphs) for the $b\bar{b}$ channel.

5. Significance

Validation: The results confirm that the Fermi Bubbles and GCE are real astrophysical phenomena and not artifacts of the Fermi-LAT instrument or analysis pipeline.
Dark Matter Constraints: The DAMPE data supports the DM annihilation hypothesis for the GCE, yielding mass and cross-section parameters consistent with the "thermal relic" cross-section ( $\sim 3 \times 10^{-26}$ cm $^3$ s $^{-1}$ ) for the $b\bar{b}$ channel.
Future Prospects: The paper highlights the potential of the proposed VLAST mission, which would offer even larger acceptance and energy range, to further resolve the nature of these diffuse sources and potentially distinguish between DM and astrophysical origins (e.g., MSPs) with higher statistical power.

In conclusion, DAMPE has successfully replicated the key findings of Fermi-LAT regarding the Fermi Bubbles and the GCE, providing an independent, high-resolution view of the gamma-ray sky that strengthens the case for a dark matter origin of the Galactic Center Excess while maintaining consistency with astrophysical background models.