On physical processes occurring in the hydrodynamic and magnetohydrodynamic astrophysical and laboratory flows

Tsiklauri, David

On physical processes occurring in the hydrodynamic and magnetohydrodynamic astrophysical and laboratory flows

Doctoral Thesis

1996

Abstract

Physics of hydrodynamic and magnetohydrodynamic flows is extensive, rapidly growing and important part of the physical science. It appears that in many cases space and laboratory plasma can be well described in the framework of the hydrodynamics or magnetohydrodynamics. In the present study we shall investigate several types of hydrodynamic and magnetohydrodynamic astrophysical and laboratory flows such as accretion disks and stellar (pulsar) winds and magnetized analog of the Couette flow, besides we also study certain basic plasma phenomena occurring in the medium under study. The structure of the thesis is following: In section II we study structure of a boundary layer of an accretion disk around nonmagnetized, rotating stellar object. In particular (Rogava & Tsiklauri, 1993), we derive the most general equations governing structure of the boundary layer and investigate the system of the equations numerically. We proposed a method for determination of the initial conditions for the system, which gave us opportunity to obtain the numerical solutions. Basing on our model we quantitatively confirmed various statements about particular features and properties of the boundary layer scattered in the literature. In section III we formulate our model (Tsikarishvili, Rogava & Tsiklauri, 1995) for relativistic, stellar (pulsar) wind with ultrarelativistic temperature basing on novel equations of state obtained in (Tsikarishvili et al., 1992). We were able to find analytical solutions of the set of relativistic hydromagnetic equations which govern the flow under consideration. In section IV, basing on the standard theory of geometrically thin accretion disks, we investigate possible observational signatures of massive balls composed by heavy, degenerate neutrinos in the vicinity of the active galactic nuclei. Using our model (Tsiklauri & Viollier, 1996) we find that if a ball of heavy neutrinos, supported by degeneracy pressure, does exist in the vicinity of the active galactic nuclei, it will cause a bump in IR region of the emitted spectrum which is observed for several AGN (Malkan, 1989). We also find that if the bump at ~ 1000K in the typical radio loud quasar 3C 273 spectrum is due to a neutrino ball, then our model implies mass of the black hole 108 M0 , a ball mass of 4 x 109 M 0 and in turn, a neutrino mass of ~3 keV /c2. In section V we switch to investigation of magnetized shear flows. Although we do not constrain ourselves with application of our results to any concrete astrophysical object, it is evident that the results of our study (Chagelishvili, Rogava & Tsiklauri, 1996a; Chagelishvili, Rogava & Tsiklauri, 19966) are applicable and relevant for a variety of the astrophysical and laboratory flows where presence of the shear is important. Basing on the novel mechanism of transformation of the magnetohydrodynamic waves in shear flow (Chagelishvili, Rogava & Tsiklauri, 1996a), we mainly focus our attention on the case when thermal pressure of the medium is anisotropic and investigate interplay of effect of presence of the shear with firehose and mirror instabilities and demonstrate a novel phenomenon - double transformation (Chagelishvili, Rogava & Tsiklauri, 1996b ). In section VI we continue consideration of problems related with basic plasma phenomena. In particular, we show theoretically (Tsiklauri, 1996a; Tsiklauri, 1996b) that in the magnetized plasma with anisotropic thermal pressure under certain conditions there should occur novel phenomenon - phenomenon of the conical refraction, which as we shall see below is quite similar to the effect well known before in crystaloacoustics and crystalooptics. We also discuss possible ways of experimental corroboration of the predicted phenomenon and address a question about its feasible usage in plasma diagnostics.

Keywords

Physics

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PhD / Doctoral

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