ASP Online Seminars: Africa’s Window to the Extreme Universe: The H.E.S.S. Telescopes and the Mystery of Cosmic Rays

by Dr Mathieu JACOBE DE NAUROIS (Laboratoire Leprince Ringuet IN2P3/CNRS - Ecole Polytechnique)

Tuesday 16 Jun 2026, 13:00 → 14:30 UTC

Abstract:

The Earth is constantly bombarded by extremely high-energy particles from the far reaches of the cosmos, known as cosmic rays. Discovered in 1912 by Victor Hess, these particles—which can be electrons, protons, atomic nuclei, or even antiparticles—may carry energy as high as that of a bullet, all concentrated in a single particle. Their impact on our daily lives is often overlooked: they contribute to irradiation during air travel, random mutations in our DNA, the production of Carbon-14 in the atmosphere, and even disruptions in electromagnetic communications.

Many cosmic phenomena appear capable of accelerating these particles, both within our Galaxy and in the distant Universe. These phenomena are linked to some of the most violent events in the cosmos: the collapse and explosion of massive stars (supernovae), the disappearance of matter into supermassive black holes, and mysterious objects such as “pulsars”, “magnetars”, “microquasars”, or “blazars”.

The H.E.S.S. (High Energy Stereoscopic System) telescope array, operating in Namibia since 2003, hunts these cosmic accelerators by detecting the very high-energy gamma rays they emit. These telescopes work in a unique way: they capture the extremely brief and faint light produced in the upper atmosphere when a gamma photon interacts with oxygen or nitrogen, triggering a cascade of secondary particles. In this process, the telescopes record thousands of images per second.

In this seminar, I will introduce the cosmic ray puzzle, explain how the H.E.S.S. telescopes operate, and recount 20 years of tracking down the astrophysical sources of cosmic rays. I will conclude by presenting the projects planned for the coming decades.

Bio of the speaker:

Prof. Mathieu de Naurois is a CNRS Senior Research Director and Professor at École Polytechnique, specializing in very high-energy gamma-ray astronomy. This cutting-edge field uses large, ultra-fast telescopes to detect the faint and fleeting Cherenkov light emitted in the atmosphere by particle cascades—triggered when a very high-energy gamma ray interacts with an atmospheric nucleus.

His work has focused on the launch and operation of the H.E.S.S. array of Atmospheric Cherenkov Telescopes in Namibia, a project run by an international collaboration of nearly 200 researchers. He has contributed to the discovery and interpretation of gamma-ray emissions from various celestial objects, including binary star systems, starburst galaxies, and supernova remnants. From 2016 to 2019, he led the H.E.S.S. collaboration and currently serves as its Deputy Director. He is also a member of the Cherenkov Telescope Array Observatory (CTAO), the next-generation gamma-ray observatory under construction, set to succeed H.E.S.S. in 2028. He currently holds the position of Vice-Chair of the CTAO Council, the observatory’s primary governing body.

In 2017, Mathieu de Naurois was awarded the CNRS Silver Medal for his outstanding contributions to gamma-ray astronomy.

ASP-Seminar_june2026.mp4

deNaurois_ASP_2026_v2-small.pdf