About this Research Topic
Instabilities are ubiquitous in astrophysical and space plasmas. From the largest molecular clouds to the velocity distribution function of particles in the heliosphere, instabilities are key to understanding properties of the partially or fully ionized gas which constitutes most of the observable Universe. At the largest, fluid scales, they drive systems out of equilibrium, enabling energy conversion. In stellar convective zones, magneto-convective instabilities lead to dynamo action that provides a way to sustain large scale magnetic fields against ohmic dissipation. In accretion disks, the magneto-rotational instability is believed to trigger a turbulent cascade within the sheared Keplerian structure leading to dissipation, angular momentum transport and wind launching, changing the accretion dynamics. The Weibel instability is considered a possible mechanism for the production of long-lived magnetic fields and energetic particles in GRBs and pulsar winds, and also plays an important role in the downstream region of relativistic collisionless shocks. Heat flux instabilities contribute to heat flux regulation in the solar wind. The fast tearing mode instability, leading to plasmoid formation, enables rapid reconnection in collisional and collisionless plasmas, playing a fundamental role in magnetic energy conversion and particle acceleration from heliospheric to extragalactic plasmas.
Instabilities are often closely related to the onset of cascading processes, as astrophysical flows rarely possess enough dissipative mechanisms at large scales, and are characterized by very high Reynolds (or Lundquist) numbers. At the smallest, kinetic scales, instabilities are a fundamental self-regulatory process. In weakly collisional flows, like the solar wind, mirror, whistler, cyclotron and firehose instabilities are observed to limit temperature anisotropies, effectively preventing the velocity distribution function from evolving too far away from an isotropic Maxwellian distribution and allowing the solar wind to retain fluid-like behavior. Instability onset and early evolution can be studied analytically. Analytical developments are, however, often limited to the linear growth phase, which makes numerical simulations the ideal way to study the non-linear and saturated stage where much of the feedback of the instabilities on the system occur.
Observations and in situ measurements are key to compare and drive simulations and theory. The coming decade will see the results of a new generation of interplanetary missions. The Parker Solar Probe and the Solar Orbiter have already brought measurements of the heliosphere closer to the Sun than ever before, discovering structures that will undoubtedly change our understanding of the solar wind and of the role of instabilities in it. The heliosphere is our best laboratory to study collisionless plasmas and these measurements will unravel behaviors ubiquitously shared by many astrophysical flows.
This Research Topic aims to gather cross-disciplinary contributions on plasma instabilities, in order to foster collaborations among different communities. We welcome advances on instability-driven astrophysical processes through theoretical developments, numerical simulations or observations. They can also tackle methodological aspects, to extract, for instance, information on the transition to the non-linear regime.
This Research Topic has been realized in collaboration with Dr. Munehito Shoda, JSPS Research Fellow at the Solar Science Observatory, National Astronomical Observatory of Japan.
Instabilities are often closely related to the onset of cascading processes, as astrophysical flows rarely possess enough dissipative mechanisms at large scales, and are characterized by very high Reynolds (or Lundquist) numbers. At the smallest, kinetic scales, instabilities are a fundamental self-regulatory process. In weakly collisional flows, like the solar wind, mirror, whistler, cyclotron and firehose instabilities are observed to limit temperature anisotropies, effectively preventing the velocity distribution function from evolving too far away from an isotropic Maxwellian distribution and allowing the solar wind to retain fluid-like behavior. Instability onset and early evolution can be studied analytically. Analytical developments are, however, often limited to the linear growth phase, which makes numerical simulations the ideal way to study the non-linear and saturated stage where much of the feedback of the instabilities on the system occur.
Observations and in situ measurements are key to compare and drive simulations and theory. The coming decade will see the results of a new generation of interplanetary missions. The Parker Solar Probe and the Solar Orbiter have already brought measurements of the heliosphere closer to the Sun than ever before, discovering structures that will undoubtedly change our understanding of the solar wind and of the role of instabilities in it. The heliosphere is our best laboratory to study collisionless plasmas and these measurements will unravel behaviors ubiquitously shared by many astrophysical flows.
This Research Topic aims to gather cross-disciplinary contributions on plasma instabilities, in order to foster collaborations among different communities. We welcome advances on instability-driven astrophysical processes through theoretical developments, numerical simulations or observations. They can also tackle methodological aspects, to extract, for instance, information on the transition to the non-linear regime.
This Research Topic has been realized in collaboration with Dr. Munehito Shoda, JSPS Research Fellow at the Solar Science Observatory, National Astronomical Observatory of Japan.
Keywords: plasmas, astrophysics, instabilities, theory, numerical simulations, observations
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