The Galactic center is a dense knot of gas, stars, and magnetic fields, where the supermassive black hole Sagittarius A* coexists with young star clusters and supernova remnants. Related studies focus on the gamma-ray background, cosmic rays, and fast radio bursts, but our work stands apart: it is the first to apply a three-dimensional spectro-morphological analysis to the entire region. Previous observations could not separate the diffuse ridge emission from background sources, leaving the nature of the particle accelerator an open question.
Observations were conducted from 2004 to 2020 with the four H.E.S.S. telescopes in Namibia, accumulating 365 hours of exposure at zenith angles below 40 degrees. Data were analyzed with the gammapy package: a three-dimensional model of the molecular gas distribution was built from CS and CO line data, then multiplied by a cosmic-ray density falling as 1/r from the center. Simultaneously, the spectra of four point sources, large-scale Galactic emission, and residual hadronic background were fitted, with nuisance parameters included to account for systematic uncertainties.
The gamma-ray spectrum of the Galactic center ridge is better described by a curved model than a simple power law, with a curvature significance exceeding 3σ. The break corresponds to parent proton energies of 15–50 TeV (or a cutoff at 60–160 TeV). The cosmic-ray density falls from the center as $r^{-1}$.10±0.05, consistent with continuous injection. The pulsar wind nebula G0.9+0.1 shows, for the first time, a significant spectral cutoff at an energy of about 5 TeV. The location of the injection source is constrained to within ~20 pc of Sagittarius A*, ruling out the Arches and Quintuplet clusters as the dominant contributor.
This work is the first to isolate the true ridge spectrum, separating it from background components, which was previously impossible due to uncertainties. Unlike neighboring studies that focused on individual sources or averaged spectra, here a three-dimensional approach linking gas and cosmic rays is applied. This allows a rigorous test of the continuous injection hypothesis and constrains the accelerator parameters.
Future telescopes such as CTAO, SWGO, and LHAASO will be able to measure the morphology of emission at energies above 30 TeV, where the spectral shape differs between models. This will help determine whether the break is due to particle acceleration or propagation in a turbulent medium. Additional data on the line-of-sight positions of molecular clouds will refine the three-dimensional model of the central zone.
The results will influence models of cosmic-ray acceleration near supermassive black holes and our understanding of the energy budget of the Galactic center.
Check the energy dependence of the cosmic-ray profile to distinguish a diffusion break from an injection break. Compare the ridge spectrum with HAWC data above 10 TeV to choose between a log-parabola and a broken power law.
In cosmic-ray physics, the maximum energy achievable in Galactic accelerators remains an open question. The observed break at 15–50 TeV directly constrains sources in the Galactic center and helps calibrate diffusion models in turbulent media.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The study analyzes 365 hours of H.E.S.S. observations of the central molecular zone using a three-dimensional model of gas and cosmic rays. For the first time, the gamma-ray spectrum of the ridge is extracted with significant curvature, corresponding to proton energies of 15–50 TeV. A constraint is placed on the position of the injection source within ~20 pc of Sagittarius A*, ruling out the Arches and Quintuplet star clusters as the main contributors.
Where its strength is
The strength of the work lies in the application of three-dimensional spectro-morphological analysis, which allowed separating the diffuse ridge emission from background components, something previously impossible. This provides a stringent test of the continuous cosmic-ray injection hypothesis and constrains the accelerator parameters.
Where it could go next
Worth trying
Why this may matter
The results could serve as a foundation for a more detailed understanding of particle acceleration mechanisms near supermassive black holes and their role in the Galactic energy budget. Isolating the true ridge spectrum opens the way to testing models of ultra-high-energy cosmic-ray origin.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.57, against a usual 0.64. It looks like few have drilled nearby.
The central molecular zone contains about 10% of the Galaxy's total molecular gas while occupying only 1% of its volume, making it the densest gas reservoir in the Milky Way.