Signals from another galaxy

Thanks to a network of state-of-the-art telescopes, an international team of researchers has just detected three sources of very high-energy gamma rays in another galaxy. A first that may tell us more about the origin of these mysterious cosmic rays.
Three sources of gamma radiation in the Large Magellanic Cloud, a satellite galaxy of the Milky Way, have just been detected by the telescopes of the HESS observatory. It's a remarkable discovery, since it's the first time these phenomena have been detected beyond our own galaxy. These messages from the past (170,000 years ago) would have a lot to tell us...

Invisible to the human eye

Gamma rays? " Concentrates of energy. A thousand billion times more energetic than visible light, these ʺgrains of lightʺ lie beyond X-rays, in a wavelength range invisible to the human eye," explains Matthieu Renaud, astrophysicist at the Laboratoire Univers et Particules in Montpellier.
Spotting them therefore requires a very special kind of instrument. " As they enter the Earth's atmosphere, these gamma rays emit a very faint flash of bluish light (Cherenkov light), which the cameras of the telescopes in the HESS experiment are able to detect ". Located in Namibia, this network of four 13 m telescopes, recently completed by a gigantic 28 m telescope, is one of the most sensitive gamma-ray detection instruments in the world.

Mysterious cosmic rays

If specialists are so enthusiastic about the discovery, it's because the observation of these rare phenomena will undoubtedly tell us a little more about the origin of "cosmic rays", the stream of particles that seems to be present everywhere in the universe, and in which the Earth is permanently immersed.
A particularly stubborn mystery: discovered in 1912 by Austrian physicist Victor Franz Hess, these extraterrestrial particles still haven't told us where they come from...
" We may be able to find out thanks to gamma rays. They are the best witnesses to extreme events in the universe: supernovae and their remnants, or pulsars and their wind nebulae, the result of the evolution of massive stars. They are very good suspects in our investigation into the origin of cosmic radiation ," explains Matthieu Renaud.

New horizons for astronomy

A pulsar nebula, a supernova remnant and also a "superbubble" (a structure formed by the powerful winds of massive stars and their supernova explosions): these are the sources of the gamma rays just observed with HESS.
Ten years ago, only a few very high-energy gamma-ray sources were known to exist in the vastness of the sky. Today, more than a hundred have been counted, thanks to gamma-ray telescopes such as HESS II, the largest of them, which have recently opened up a new window of observation in astronomy.