High-energy astrophysics at MPIK is characterized by a very close cooperation between experimentalists coming from a particle physics background and the more theoretically oriented astrophysicists. They study the non-thermal phenomena in the Universe using the High-Energy Stereoscopic System H.E.S.S. to detect very-high-energy (VHE) gamma rays from the cosmos, and investigate the acceleration mechanisms in cosmic sources of high-energy particles.

Particles in the VHE range cannot be produced as thermal radiation, like the electromagnetic radiation in most other wavelength regimes; only in the Big Bang high enough temperatures were reached for a short time. Instead, collective non-thermal mechanisms are believed to be responsible for the acceleration: charged particles continue to gain energy by diffusively returning many times into the shock front of the giant shock waves generated in supernova explosions or in the plasma jets emerging from the immediate vicinity of the massive black holes at the centres of active galaxies. Considerable effort at the Institute is going into the modelling and theoretical description of processes within the different types of cosmic accelerators.

The VHE gamma rays detected on Earth are secondary products generated when the accelerated primary charged particles react with the ambient medium – either the interstellar gas or the ambient photon fields. In contrast to the charged particles, the gamma rays travel on a straight path from the source to the observer and allow imaging of sources and studying the processes in the acceleration region.

Since the H.E.S.S. telescopes became fully operational in early 2004, they detected more than 60 VHE gamma-ray sources along the Milky Way such as supernova remnants or pulsar wind nebulae, that are visible in other wavebands, from radiowaves to X-rays, too. But there is also a number of unidentified, so-called dark sources. Of special interest is the region of the Galactic Centre which harbours a supermassive black hole, meanwhile proven to be associated with a gamma-ray source. Beyond our Galaxy, galaxies with active nuclei, starburst and radio galaxies are found as faint objects in the VHE gamma light. To understand the objects, in many cases a multi-wavelength analysis is required.

Infrared emission from dust is a direct tracer of the interstellar matter and radiation fields with which cosmic rays interact to produce gamma rays. Researchers at MPIK are concerned with the development and application of models for the combined analysis of the direct UV/visible and dust re-radiated infrared light from galaxies.

Division Hofmann

Theoretical Astrophysics (pdf)
H.E.S.S.: Cosmic Accelerators in the Light of Gamma Rays (pdf)

High-energy gamma rays from space – a trillion times more energetic than visible light – do not reach the Earth’s surface. Nevertheless, they can be sighted at the ground with the atmosphere serving as a detector. When entering the atmosphere, the gamma quanta collide with molecules producing cascades of electrically charged secondary particles, so-called particle showers. These emit faint bluish and extremely short flashlight (Cherenkov light) which illuminates a circular area of about 250 m diameter on the ground and can be detected in dark moonless nights with large reflector telescopes that are equipped with fast photosensors. To trace the exact direction from which the particle showers come, they are observed stereoscopically by several telescopes simultaneously.

The High-Energy Stereoscopic System H.E.S.S. consists of four identical telescopes of each 107 m² mirror area forming the corners of a square of side 120 m. A “camera” – a matrix of 960 photosensors – in the focus of each mirror covers a large field of view. Thus, the instrument is especially suited for sensitive sky surveys. H.E.S.S. was the first instrument to resolve the shells of supernova remnants in VHE gamma rays. In the centre of the array, a fifth, huge telescope with 600 m² mirror area is close to completion. This will strongly enhance the sensitivity of the system and extend the observable energy range to lower energies. The location on the southern hemisphere in Namibia provides a direct view into the centre of our Galaxy.

The next generation of instruments for very-high-energy gammy-ray astronomy will be CTA, the Cherenkov Telescope Array, which is already in preparation.

Division Hofmann

H.E.S.S.: Cosmic Accelerators in the Light of Gamma Rays (pdf)

Today, the entire visible Universe is made of matter rather than antimatter. Since particles and antiparticles were created in equal amounts in the Big Bang, there must be a fundamental difference between them. Else, they would have completely annihilated, leaving a Universe filled with pure radiation. The LHCb experiment at the Large Hadron Collider (LHC) of CERN in Geneva tries to solve this puzzle and searches for physics beyond the established Standard Model. By investigating rare decays of heavy quarks first evidence for different particle/antiparticle behaviour was found. In 2011 LHCb started the search for so-called new physics in B-meson decays. Physicists and electronic engineers at MPIK have developed, produced and tested radiation-hard electronics components for the silicon tracker of LHCb which records trajectories of charged particles. Now, the scientists are strongly involved in the data analysis which demands advanced methods.

MPIK also works on the preparation of ultracold negative ions which could serve to cool antiprotons, which are a prerequisite for the production of cold antihydrogen by recombination with positrons. This will open the field of direct high-precision studies on antimatter properties, e. g. its free fall in the Earth’s gravitational field. Further, with a single proton or antiproton confined in a Penning trap at very low temperature, their magnetic moments can be accurately determined to test fundamental symmetries.

Division Hofmann    Division Blaum    Group Kellerbauer

The LHCb Experiment: B-Physics, Antimatter and Dark Matter (pdf)
Precision Measurements with Antimatter: Antihydrogen in the Laboratory (pdf)
Precision Experiments in Penning Traps: Measurements on Single Ions (pdf)