The prestigious Physical Review Letters published another article co-authored by Frederico Fiuza, a professor at Instituto Superior Técnico and principal investigator at the Group of Lasers and Plasmas of the Institute for Plasmas and Nuclear Fusion (IPFN). This time, the Técnico professor, together with colleagues from the Sorbonne University (France), Princeton University (USA) and the National Institute of Natural Sciences of Japan, focussed on phenomena associated with stellar explosions.
When stars explode, their remnants drive violent shock waves that heat electrons in the interstellar medium to three orders of magnitude above the temperature expected from adiabatic compression on the shock. The mechanisms behind this heating have remained a long-standing puzzle, but the article now published presents a new theory for the energy partition between electrons and ions in such strong shock waves.
Initially, most of the energy in these shocks is carried by the ions, which are much heavier than electrons. Because these shocks are collisionless, collective electromagnetic processes must be responsible for exchanging energy between the ions and the electrons at the shock. The authors show that the difference in inertia between electrons and ions leads to differential scattering between the two species in the turbulent magnetic field produced ahead of the shock, driving an electric field. It is this electric field that, in turn, leads to efficient electron heating in a Joule-type process, with electrons acquiring a temperature that is a significant fraction of that of the ions, as inferred from astronomical observations.
The theoretical model is validated against first-principles simulations showing very good agreement. Its generality opens up promising avenues for studying electron transport and heating in different settings dominated by magnetic turbulence (which ranges from stellar explosions to fusion plasmas).
This work was carried out in the context of the project “Extreme Particle Acceleration in Shocks: from the laboratory to astrophysics” (XPACE), which was awarded a Consolidator Grant by the European Research Council (ERC) in 2023. Frederico Fiúza was recently honoured with the Lev D. Landau and Lyman Spitzer Jr. award for his contribution to plasma physics.
*This text was written in collaboration with the Institute for Plasmas and Nuclear Fusion (IPFN).
