Astrophysique à Haute Energie

Le centre de notre galaxie abrite un trou noir super-massif (SMBH) d'environ 4 10⁶ Msol, associé à une source radio compacte appelée Sgr A*. Avec une luminosité bolométrique huit ordres de grandeur en dessous de sa luminosité d'Eddington, son émission actuelle parait très faible. L’émission de Sgr A* présente également des sursauts fréquents (quasi quotidiens) observés du domaine radio aux X-durs. Il apparait maintenant acquis que ces sursauts sont dus à l’accélération rapide d’électrons jusqu’à des énergies dépassant la dizaine de GeV au voisinage du trou noir.

Stars form due to the gravitational collapse of dense molecular clouds. The process of star formation is still not completely understood, but it is believed that a crucial parameter that regulates star formation is the ionization level in the dense cores of molecular clouds. This is because the ionization level is determining the coupling between the gas and the magneticl field, which is in turn affecting the dynamics of the collapse through magnetic pressure support.

Cosmic rays are relativistic particles that hit continuously the Earth's atmosphere from outer space. Understanding the origin of these cosmic particles, and how they acquire their energy is one of the most important open problems in high energy astrophysics. 

The origin of PeV cosmic rays is a crucial issue in cosmic ray physics. The chemical composition of cosmic rays is dominated by protons below a particle energy of ~1 PeV, while heavier nuclei become important above it. This, together with the evidence that the transition between galactic and extragalactic cosmic rays takes place at particle energies largely exceeding the PeV, implies that the sources of galactic cosmic rays must be proton PeVatrons  

Cosmic rays are high energy particles reaching our planet, whose spectrum  ranges from sub GeV up to 10^10 GeV energies. The bulk of the observed cosmic rays, probably up to PeV energies, is likely of galactic origin and is thought to be accelerated at supernova remnant shocks and to propagate diffusively through the Galaxy. The acceleration mechanism, the escape of accelerated particles from the sources and their subsequent propagation toward us and out of the Galaxy, are all pieces of the same complex puzzle, namely the origin of cosmic rays. A fascinating and yet not

L'expérience H.E.S.S.-2 (High Energy Stereoscopic System) [1] est un réseau de télescopes Tcherenkov  mesurant des rayons gamma dans le domaine des très hautes énergies (au-delà de ~30GeV). Cet observatoire est un des instruments au sol les plus performants au monde : grâce à son grand champ de vue, sa bonne résolution angulaire et sa grande sensibilité il permet de détecter et d'étudier l'émission gamma de sources galactiques aux plus hautes énergies.

The center of our Galaxy hosts a Super-Massive Black Hole (SMBH). Since it has been argued that the SMBH can accelerate particles up to very high energies, its current and past activity must contribute to the population of Galactic cosmic-rays (CRs), the energetic particles that pervade the Galaxy.

The center of our Galaxy hosts a Super-Massive Black Hole (SMBH). Since it has been argued that the SMBH can accelerate particles up to very high energies, its current and past activity must contribute to the population of Galactic cosmic-rays (CRs), the energetic particles that pervade the Galaxy. Ten years ago the HESS experiment has reported a bright TeV point-like source at a position compatible with that of the SMBH. After subtraction of this point source, a diffuse emission stretching over few degrees along the Galactic longitude was revealed.

L'effondrement gravitationnel qui marque la mort d'une étoile massive engendre la plupart du temps une étoile à neutron fortement magnétisée en rotation rapide: un pulsar. Comme ces événements sont rares on connaît très mal la distribution des périodes de rotation à la naissance qui peuvent aller de quelques ms à quelques centaines de ms. Les pulsars ralentissent très rapidement et leur énergie rotationnelle est convertie en un vent de particules chargées relativistes qui, une fois confinées par le milieu ambiant, créent une nébuleuse de pulsar.