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........ published in NEWSLETTER # 59
SOLAR AND ASTROPHYSICAL MAGNETOHYDRODYNAMIC FLOWS
by Professor K. Tsinganos, University of Crete, Heraklion (Greece)
A conceptual revolution in astronomy has been the prediction that an extremely hot solar corona cannot be confined by solar gravity, but expands supersonically into interplanetary space to fill the whole solar system. Modern observations including those recently with the Hubble Space Telescope, have revealed that the Universe is replete with analoguous outflows from all kinds of objects, ranging from the rich varieties of stars to the galaxies.
This volume (NATO ASI SERIES C481) contains review lectures presented by leading plasma astrophysicists at the NATO Advanced Study Institute (ASI) on "Solar and Astrophysical Magnetohydrodynamic Flows", held in Heraklion, Crete, Greece, in June 1995. The book is dedicated to E.N. Parker, who initiated the MHD approach to describe such cosmical phenomena, on the occasion of his retirement from the University of Chicago, after almost 50 years in solar physics and astrophysics.
The first part is on solar plasmas and the second on astrophysical MHD flows, with emphasis on their common hydromagnetic physics. The generation, storage and eruption of magnetic fields in our Sun deep in its convective layers, can be seen as a prototype of the fields of other stars, galaxies and accretion disks. The eruption through the photosphere magnetic field forms intense flux tubes and sunspots with siphon flows, Alfven waves and turbulence. The impressive high resolution pictures of the Sun in X-rays by the Yokhoh satellite show such an atmosphere constituted of many steady and transient magnetic loops with clear evidence of intense heating due to magnetic reconnection, anticipated by the spontaneous formation of electric current sheets. A similar picture emerges from numerical simulations of solar and astrophysical plasmas, such as magnetic loops, flares, solar X-ray jets, the nonlinear evolution of the Parker instability and magnetically accelerated astrophysical jets. Recent data from the south and north solar polar pass of the ULYSSES spacecraft present evidence that the solar wind is indeed a meridionally anisotropic outflow, perhaps similar to winds from solar- as well as non-solar-type stars.
In the second part of the book the recent Hubble Space Telescope observations of galactic and extragalactic jets show explicitly their association with accretion disks and intricate structure, while jets associated with symbiotic stars and observed superluminal outflows in the Milky Way have similar properties. A theoretical understanding of such observations can be provided by theorems on the general tendency of rotating magnetized outflows to focus towards the system axis, or, self-similar analytical models of MHD flows exhibiting novel physical properties of the MHD equations, useful in modelling MHD flows. The second part of the book is complemented by a comprehensive review of the Parker instability and subsequent star formation in the frame of multifluid MHD, physical properties in accretion disks with embedded magnetic fields and studies of relativistic MHD outflows.
Reference books: C68, C342, C373, C375, C422, C481
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