Christoph's photo Christoph Pfrommer
Back to Lectures overview

    A pedagogical guide to cosmic rays and magnetic fields in the universe

    More than one century after the discovery of cosmic rays and 50 years after the first observation of an ultra high-energy cosmic ray with an energy exceeding 1e20 eV is their origin still a mystery and represents a major problem in theoretical astrophysics. The challenge consists of understanding the astrophysical environment and process that is able to accelerate an elementary particle to a kinetic energy which is equal to that of a golf ball traveling at about 100 km/h. In addition, we observe magnetic fields to be ubiquitous in the universe and to range from small planetary scales to large cosmological scales. In this lecture, we will learn about astrophysical mechanisms to accelerate charged elementary particles to extreme energies so that they form the population of cosmic rays and discuss how these particles are transported in galaxies. In addition, I will explain how magnetic fields are generated and amplified and will discuss how they can influence the dynamics of astrophysical systems. Finally, I will show that our modern-day understanding of galaxy formation requires a knowledge of these non-thermal components and demonstrate that they could hold the key to the physics of feedback by star formation and active galactic nuclei, which appears to be critical in obtaining realistic disk galaxies and to slow down star formation to the small observed rates. The course is aimed at master and PhD students of physics and astrophysics and will show the simplicity of this apparently complex physics by demystifying the topic; as such, it will hopefully answer questions about these topics that you may have and previously did not dare to ask.


    • Magnetic fields:
      • Generating magnetic fields: Biermann battery
      • Evolution of magnetic fields: magneto-hydrodynamics
      • Magneto-hydrodynamic waves and turbulence
      • Magnetic draping

    • Cosmic rays:
      • General properties and cosmic ray-wave interactions
      • Diffusive shock acceleration
      • Second-order Fermi acceleration
      • Cosmic ray transport

    • The physics of galaxy formation:
      • Puzzles in galaxy formation
      • Stellar feedback
        • Supernova feedback
        • Radiation feedback
        • Cosmic ray feedback
      • AGN feedback
        • Supermassive black holes
        • AGN jet feedback
        • Quasar feedback


    1. Lectures on Magnetic fields
    2. Lectures on Cosmic rays
    3. Lectures on The physics of galaxy formation
    4. Derivation of Fermi-I acceleration