CRC 963 Astrophysical Flow Instabilities and Turbulence

CRC 963 Astrophysical Flow Instabilities and Turbulence

In astrophysics and cosmology, fluid flow occurs on a large range of scales and under very different conditions, from the dense interior of stars and planets to the highly rarefied intergalactic medium. These flows share the fact that they are generally turbulent, i.e. highly disordered both in space and time. Most astrophysical flows occur under conditions where the driving forces generate large fluctuations in velocity and pressure with important consequences for the transport of energy and mass. Turbulence is one of the key processes for the structure and evolution of a large variety of geo- and astrophysical systems. Astrophysical turbulence and instabilities occur in connection with rotation, convection, and magnetic fields. The universality of astrophysical turbulence interlinks the physics of the interior of planets or stars with protoplanetary or galactic disks, as well as the intergalactic gas outside of galaxies. For example, angular momentum transport by turbulence is a central question that must be answered to understand how galaxies or stars form, how protoplanetary disks evolve, how metals are mixed in the interstellar and intergalactic medium, or how differential rotation is established in stars and planets. Magnetic field amplification through turbulent dynamo processes is ubiquitous in planets, stars, and galaxies. The onset of instabilities due to dust particles or newly formed planets in protoplanetary disks controls the properties of the evolving structures. We can observe a variety of interactions between stars, planets and galaxies with their environment leading to the exchange of energy and (angular-) momentum.
This compilation highlights the enormous potential and perspective of a collaborative effort to investigate the common underlying physical processes. Our combination of projects will enable us to understand aspects of turbulent magnetic field amplification, turbulence and instabilities of rotating fluids, and in the interaction of turbulence and instabilities with radiation, gravitation, or dust particles and hence answer fundamental questions about the formation and evolution of galaxies, stars, and planets.

Subprojects with involvement of the MPS department "Sun and Heliosphere":

A2 From solar to heliospheric flows and instabilities (Joerg Buechner, MPS and Volker Bothmer, Institute for Astrophysics of the University of Göttingen)

Space missions currently in orbit enable for the first time to continuously image the generation and propagation of coronal mass ejections (CMEs) flows from the Sun to beyond the orbit of Earth. Project A2 will help clarify the role of magnetic reconnection processes for CME onset and acceleration by applying the 3D MHD code LINMOD3D to the state of the art solar and heliospheric observations. Complementary analysis of the modeling results for the onsets of CMEs and the turbulence parameters derived from the imaged CME and associated shock waves will lead to fundamental new understandings of the generation of heliospheric instabilities through CMEs.

A15 Simulations of reconnection and dynamo action in turbulent plasma flows (Joerg Buechner, MPS and Wolfram Schmidt, Institute for Astrophysics of the University of Göttingen)

The macroscopic phenomena dynamo and reconnection require energy dissipation on micro-scales. Since astrophysical plasmas are usually hot and dilute, binary particle collisions cannot provide an irreversible energy conversion to heat. Instead, perhaps turbulence couples macroscopic motions to collisionless energy dissipation on microscales. The physical nature of magnetic turbulence and its consequences for dynamos and reconnection is a fundamental open problem, e.g. due to the involved non-linearity and non-locality of the interactions as well as the large range of scales, which have to be bridged. We address this problem by advanced numerical simulations.

A16 Origin and structure of magnetic fields in cool stars (Manfred Schuessler, MPS and Ansgar Reiners, Institute for Astrophysics of the University of Göttingen)

The origin of cool star magnetic fields and their effects on stellar atmospheres, planet formation, and planetary companions are long-standing open problems. The generation of magnetic flux in electrically conducting fluids in turbulent motion is of fundamental importance for understanding magneto-hydrodynamic turbulence at large Reynolds numbers. We propose an interdisciplinary approach to address the astrophysical and turbulence aspects of stellar surface magnetism by using radiative MHD simulations of near-surface stellar magnetoconvection on the one hand, and by obtaining reliable quantitative observations of magnetic fields in stars from sun-like to very-low mass stars on the other.


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