Dynamics of Relativistic Magnetized Flows.

Lead Research Organisation: University of Leeds
Department Name: Applied Mathematics

Abstract

Magnetically-dominated relativistic outflows are naturally generated as extentions of magnetospheres of rapidly rotating black holes and neutron stars. They are powered by the rotational energy of the central object and carry out this energy mainly in the form of Poynting flux. When this energy is dissipated via interaction with external medium, strong sources of non-thermal electromagnetic emission are produced. This is how the origin of Pulsar Wind Nebulae, Radio Galaxies, Quasars, Galactic Micro-quasars and GRB jets is often explained in modern theoretical astrophysics. However, these theories are based on simplistic analytical and semi-analytical models of the flow dynamics and the numerical studies have been confined mostly to the case of axisymmetric flows so far. On the other hand, many magnetic configurations are known to be unstable with non-axisymmetric modes growing at highest rates in linear regime. Until the non-linear effects of these instabilities are fully understood these theories are not complete. In fact, a number of long standing problems in the theory of Pulsar Wind Nebulae and Extragalactic Jets could reflect the limitations of imposed axisymmetry. One of such problems is the very slow rate of conversion of the Poynting flux into the kinetic energy, the so-called 'sigma-problem'. The randomization of magnetic field due to the instabilities may significantly improve the efficiency because the dynamics of random magnetic field mimics that of ultra-relativistic gas. We propose to use massive parallel relativistic MHD simulations in order to study the complex three-dimensional dynamics of magnetically dominated relativistic flows. The recent progress in development of robust numerical schemes for RMHD and Adaptive Mesh Refinement algorithms combined with availability of powerful computer clusters make this project both feasible and timely. We have been involved in the development of Computational Astrophysics of Relativistic Plasma from the very beginning and have accumulated internationally-recognised expertise in the area.

Publications

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Barkov M (2014) A multidimensional numerical scheme for two-fluid relativistic magnetohydrodynamics in Monthly Notices of the Royal Astronomical Society

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Keppens R (2014) INTERACTING TILT AND KINK INSTABILITIES IN REPELLING CURRENT CHANNELS in The Astrophysical Journal

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Keppens R (2013) Relativistic HD and MHD modelling for AGN jets in Plasma Physics and Controlled Fusion

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Keppens R (2014) Scalar hyperbolic PDE simulations and coupling strategies in Journal of Computational and Applied Mathematics

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Kim Jinho (2015) On the linear stability of magnetized jets without current sheets - non-relativistic case in Monthly Notices of the Royal Astronomical Society

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Komissarov S (2012) Magnetic dissipation in the Crab nebula in Monthly Notices of the Royal Astronomical Society

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Komissarov SS (2015) Stationary relativistic jets. in Computational astrophysics and cosmology

 
Description 1. We have carried out the most advanced ever simulations of nebulae created by magnetized relativistic winds (PWN) from neutron stars and laid out the foundations of their current theory. In particularly, we have established the importance of magnetic dissipation inside the nebulae and hence explained how the deduced high magnetization of the winds can agree with the observed low magnetization of the nebulae (the so-called sigma-problem, which remained unresolved for about thirty years). 2. The jets of active galaxies appear incredibly stable - if the gaseous jets produced by rocket engines were that stable they would be able to reach all the way to the Moon unscathed. We have found a way to explain this apparent stability, as well as to show how the instabilities may eventually develop in these jets. The theory has been supported by our advanced computer simulations of relativistic magnetized plasma jets using an ingenious modification of the traditional setup used in previous studies of this type.
Exploitation Route Our findings set new directions for modern astrophysical research in the field of relativistic astrophysics.
Sectors Education,Other

URL http://adsabs.harvard.edu/abs/2014MNRAS.438..278P
 
Description Public lectures on the Astrophysics of the Crab Nebula. Leeds Astronomy Club
First Year Of Impact 2014
Sector Other
Impact Types Cultural

 
Description Astrophysics of Crab Nebula 
Organisation Catholic University of Louvain
Department Department of Mathematics
Country Belgium 
Sector Academic/University 
PI Contribution Theoretical investigation of Pulsar Wind Nebulae and Astrophysical jets. Computer simulations.
Collaborator Contribution The computer code ARMVAC and technical assistance with its utilization.
Impact Numerous publications
Start Year 2012
 
Description Astrophysics of Crab Nebula 
Organisation Purdue University
Department Department of Physics and Astronomy
Country United States 
Sector Academic/University 
PI Contribution Theoretical investigation of Pulsar Wind Nebulae and Astrophysical jets. Computer simulations.
Collaborator Contribution The computer code ARMVAC and technical assistance with its utilization.
Impact Numerous publications
Start Year 2012
 
Description Stability of astrophysical jets 
Organisation University of Notre Dame
Department Department of Physics
Country United States 
Sector Academic/University 
PI Contribution Joint study of the jet stability problem
Collaborator Contribution Joint study of the jet stability problem
Impact Joint publication in a scientific journal.
Start Year 2015
 
Description poular science article 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? Yes
Type Of Presentation Paper Presentation
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Article Porth, Keppens, "In the heart of the Crab Nebula"
september issue 2013, pages 106-109 ( in dutch).

Wider dissemination of our results
Year(s) Of Engagement Activity 2013