Session H03: From the Sun to the Highest Energies in the Universe

Live

Cosmic rays are the highest energy messengers of astrophysical phenomena in the Universe. The sources of these particles are unknown and it is one of the great puzzles of modern astrophysics how they are accelerated to macroscopic energies of $>10^{20}$ eV. In this talk I will highlight recent experimental results on ultrahigh-energy cosmic rays and discuss their implications on our understanding of the physics and astrophysics at extreme energies.   

Live

More than 70 years after Enrico Fermi's seminal paper \textit{On the Origin of the Cosmic Radiation}, Fermi acceleration is still one, if not the most, prominent mechanism for producing non-thermal particles. I outline how the latest observations compare with the modern theory of cosmic ray acceleration, assessing the crucial role of kinetic plasma simulations in validating and furthering classical and newly-proposed models. In particular, I discuss the two flavors of Fermi mechanisms potentially responsible for the energization of both Galactic and extragalactic cosmic rays, namely diffusive shock acceleration in supernova remnants and \textit{espresso} acceleration in the relativistic jets of active galactic nuclei.   

Live

The birthplace of the solar wind is the corona of our Sun, where unidentified mechanisms heat the plasma to millions of Kelvin and magnetic pressure dominates over thermal pressure. Coronal plasma is accelerated away from the Sun by pressure gradients, becoming supersonic at a heliocentric distance of a few solar radii and super-Alfvenic at tens of solar radii. More than half a century since the theoretical prediction of the solar wind and its detection at the start of the space age many questions related to the physics of coronal and solar wind heating and acceleration remain unanswered because there have been no direct observations of the state of the plasma near the Sun. Here the first observations of the Parker Solar Probe are presented. Launched in August 2018 with its first perihelia at 35 and 27 solar radii, the probe is already the closest mission ever to the Sun, revealing young, low-Alfven-mach-number solar wind still in the grip of the Sun and solar corona. The structure of the young solar wind will be discussed, including measurements of significant rotational flows, field reversals, kinetic-scale fluctuations and other surprises. Over the next six years PSP will pass closer to the Sun culminating in encounters below 10 solar radii, but these first observations collected may already call for an overhaul in our understanding of the origin and energization of the corona and solar wind.