Speaker
Description
Astronomical observations suggest pervasive, dynamically important magnetic fields in our
Galaxy and the intracluster medium, yet their origin remains a long-standing question in
astrophysics and cosmology. It is widely believed that such fields first arose as weak “seeds”
generated by cosmic batteries and were subsequently amplified by turbulent plasma flows to
current levels via the dynamo process; however, a complete understanding of these processes
in weakly collisional plasmas, as well as the sustenance of magnetic fields once turbulent
stretching subsides, is still lacking. This work presents a unified paradigm for the origin and
evolution of cosmic magnetism by incorporating the effects of nonequilibrium microphysics of
collisionless plasmas into macroscopic astrophysical processes. Using analytical theory and
first-principles numerical simulations, it is demonstrated that seed magnetic fields can
spontaneously emerge under generic turbulent motions through kinetic plasma instabilities,
implying that cosmic plasmas are ubiquitously magnetized. The cross-scale, nonlinear coupling
between microscopic magnetic fields and macroscopic flows enhances turbulence and
accelerates the plasma dynamo, rapidly amplifying the field to energy equipartition with the
turbulent flow. The subsequent relaxation of these fields after turbulent stretching subsides is
regulated by pressure-anisotropy-driven instabilities. The ab initio production of equipartitionstrength fields from an initially unmagnetized plasma, together with their relaxation, provides a
predictive explanation for the prevalence of cosmic magnetism, a key target of upcoming
observations such as those by the Square Kilometer Array.