The term “Plasma Universe”, coined by Hannes Alfvén, emphasizes the fact that plasma phenomena discovered in the laboratory and in accessible regions of space, must be important also in the rest of the universe, which consists almost entirely of matter in the plasma state.

Relevant aspects of this concept will be discussed. They include the response of the plasma to electric currents, the support of magnetic-field aligned electric fields, violation of the frozen-field condition, rapid release of magnetically stored energy, acceleration of charged particles, chemical separation, filamentary and cellular structures, and critical velocity interaction.

Observations of solar oscillations have provided us with detailed information about the solar interior. Here I consider three examples of results obtained in such helioseismic investigations: i) the effect of the equation of state on the comparison between observed and theoretical frequencies; ii) a determination of the depth of the solar convection zone; and iii) indications of deviations from standard models of the structure of the solar core.

Neutrinos interacting with the vacuum of vector bosons and leptons possess important vacuum electromagnetic characteristics: viz., the anomalous magnetic moment Δμvacν and the mean-square radius of charge distribution <r2>1/2. As a result, neutrinos, just like neutrons, may interact with an external magnetic field.

Kinetic energy of convection is transported inwards in the main body of convection zone. The temperature gradient becomes super-radiative at the top of the overshooting zone. These two effects make the solar equilibrium model much less sensitive to the assumed mixing length in Xiong's eddy diffusion theory. Observed brightening of downflow at high level in the surface region over intergranular lanes seems to be consistent with the overshooting model. Momentum transport by convective motion is shown to be crucial in pushing down magnetic flux tubes against buoyancy. Also, subadiabatic layers are possibly formed temporarily in the middle of the convection zone, exciting oscillations and generating chaotic motions.

Dynamo theory of the solar magnetic field finds itself in a period of reappraisal since about 1980. There are two reasons for this: (1) The required increase of the angular speed Ω, with decreasing r is neither found in numerical simulations nor measured by helioseismology. (2) Mean field modeling shows often little regard for inherent physical restrictions and selfconsistency.

By analyzing the hypothesis that the solar dynamo operates in a thin layer at the bottom of the convection zone, we conclude that this hypothesis can fit observational facts only if there is turbulence with the length scale of a few hundred kilometers in and around the dynamo region.

Helioseismology provides a powerful tool for investigating stratification and dynamics of plasma in the Sun's interior. The observed frequencies of the 5-min oscillations depend on density, sound speed, chemical abundances and angular velocity distributions inside the Sun. These parameters are estimated using inversion techniques.

The evolution of the large-scale toroidal magnetic field Bϕ of the Sun generating in the radiative zone by acts of differential rotation on the relict radial magnetic field Bϕ is investigated regarding the magnetic buoyancy and ohmic dissipation.

In the framework of the magnetohydrodynamic equations with dissipative terms in the form of turbulent viscosity (Vt) the linear stage of the instability of a subphotospheric field with respect to magnetic buoyancy is considered. For an exponential in z, isothermal plane-parallel atmosphere with a constant Alfvenic velocity the perturbations of the form are described by differential equation with constant coefficients. The qualitative dependence of the growth rate of instability on transverse wave number is determined (see Figures 1 and 2) and characteristic scales of the magnetic tubes are evaluated at the linear stage of instability (Kuznetsov, 1987, 1988).

Working under the hypothesis that magnetic flux in the sun is generated at the bottom of the convection zone, Choudhuri and Gilman (1987; Astrophys. J. 316, 788) found that a magnetic flux tube symmetric around the rotation axis, when released at the bottom of the convection zone, gets deflected by the Coriolis force and tends to move parallel to the rotation axis as it rises in the convection zone. As a result, all the flux emerges at rather high latitudes and the flux observed at the typical sunspot latitudes remains unexplained. Choudhuri(1989; Solar Physics, in press) finds that non-axisymmetric perturbations too cannot subdue the Coriolis force. In this paper, we no longer treat the convection zone to be passive as in the previous papers, but we consider the role of turbulence in the convection zone in inhibiting the Coriolis force. The interaction of the flux tubes with the turbulence is treated in a phenomenological way as follows: (1) Large scale turbulence on the scale of giant cells can physically drag the tubes outwards, thus pulling the flux towards lower latitudes by dominating over the Coriolis force. (2) Small scale turbulence of the size of the tubes can exchange angular momentum with the tube, thus suppressing the growth of the Coriolis force and making the tubes emerge at lower latitudes. Numerical simulations show that the giant cells can drag the tubes and make them emerge at lower latitudes only if the velocities within the giant cells are unrealistically large or if the radii of the flux tubes are as small as 10 km. However, small scale turbulence can successfully suppress the growth of the Coriolis force if the tubes have radii smaller than about 300 km which may not be unreasonable. Such flux tubes can then emerge at low latitudes where sunspots are seen.

The possibility of the damping of plane gravitational waves while propagating in a plasma medium is considered. The gravitational plasma frequency, is for a neutron star medium ~ 103Hz, which is the same as the frequency of the gravitational waves emitted by a collapsing star. So resonant damping of such waves within a collapsing star is probable. Estimates are made for the damping length for dense and dilute plasmas (also in the presence of magnetic fields). Analogies with Landau damping are made. Applications to other astrophysical situations are outlined.

The VVO mechanism suggests that the existence of a neutrino magnetic moment would lead to variations of the observed solar neutrino flux with the magnetic activity of the Sun. The MSW mechansm suggests neutrino oscillations in the dense plasma solar interior. Assuming a non-vanishing neutrino magnetic moment and a magnetic field gradient increasing towards the solar core as required in some dynamo models, the combined effect of the oscillation and the flipping on neutrino propagation in the solar interior is studied. The effect of charge screening in scattering cross-section is also considered.

The theory of angular momentum transport by magneto-thermo-centrifugal winds is reviewed, with special reference to recent observations of rapidly-rotating young solar-type stars.

Flare-like events similar to those observed on the Sun occur on many different types of stars, particularly on late K and M dwarfs. Although the physical mechanisms responsible for these events remain largely unknown, it is likely that the flare energy derives from dissipation of magnetic fields as is the case for solar flares. We review the basic observational facts that suggest an analogy between solar and stellar flares and we discuss how the different physical conditions occurring on stars may affect the application of current solar-type models to the stellar case. We show that, in spite of a qualitative agreement found between model predictions and observations, there is still no convincing evidence that stellar flares are simply scaled-up versions of solar flares. Major advances in the observations of stellar flares are required before this fundamental question can be safely addressed.

The effect of a superstrong magnetic field on neutron stars or white dwarfs is studied for Thomson scattering in a fully ionized collisionless. plasma. The equation of motion for an electron in the presence of both the induced electric field of the plasma and a static uniform external magnetic field is used to determine the acceleration of the electron. The collective plasma effects due to the field and density fluctuations are investigated by using the test-particle picture. The scattering of a photon by a plasma is a function of the acceleration of particles by the electric field of the incident wave and the static external magnetic field Assuming that the electrons are distributed with density the radiation field far from the scattering center is where the delta function indicates that all quantities are to be evaluated at the retarded time and δλ is the angle between the wave vector and the Poynting vector, which is given by

A systematic development of the photon 4-momentum in the non-quantic perspective of General Relativity is very difficult to find in the scientific litterature. However, the photon 4-momentum is a fundamental concept if one wants to study relativistic transport theory or Compton collision formulae. For these reasons, a coherent formalism has been elaborated. It sysmetically allows one to formulate these problems the criterion of validity being the fact that in the case of the Minkowski metric, the general formulae give the classical results of the Special Relativity.

Stellar chromospheres lose energy, predominantly, via radiation and coronae via conduction, radiation and stellar wind flows. To prevent these hot layers from rapidly cooling down to photopsheric temperature some source of heating must be present.