Gamma-ray telescopes reveal a high-energy trap in our galaxy’s center


The five telescopes of the High Energy Stereoscopic System (H.E.S.S.), located in Namibia, capture faint flashes that occur when ultrahigh-energy gamma rays are absorbed in the upper atmosphere. A new study of the galactic center combines high-energy observations from H.E.S.S. with lower-energy data from NASA’s Fermi Gamma-ray Space Telescope to show that some of the speediest particles become trapped there. Credit: H.E.S.S., MPIK/Christian Foehr

In March 2016, scientists with the H.E.S.S. Collaboration reported gamma-ray evidence of the extreme activity in the galactic center. The team found a diffuse glow of gamma rays reaching nearly 50 trillion electron volts (TeV). That’s some 50 times greater than the gamma-ray energies observed by Fermi’s Large Area Telescope (LAT). To put these numbers in perspective, the energy of visible light ranges from about 2 to 3 electron volts.

The Fermi spacecraft detects gamma rays when they enter the LAT. On the ground, H.E.S.S. detects the emission when the atmosphere absorbs gamma rays, which triggers a cascade of particles resulting in a flash of blue light.    

In a new analysis, published July 17 in the journal Physical Review Letters, an international team of scientists combined low-energy LAT data with high-energy H.E.S.S. observations. The result was a continuous gamma-ray spectrum describing the galactic center emission across a thousandfold span of energy.


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