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The linear stochastic hydrodynamical equations of the radiation-matter-one-component fluid in the Universe before the recombination era are solved. The stochastic forces in the heat flux and the viscous stress tensor are described according the procedure of Landau and Lifshitz. In the case of a low density universe, where the effects of the thermal conductivity can be neglected with respect to the shear viscosity, we find analytical solutions of the dispersion relation for the different modes and of the density correlation function
. At the very Jeans length, this density correlation function exhibits a linear (for very large times) or a cubic (for small times) time dependence instead of a frozen-in character of this special mode. 相似文献
2.
Ekkehard Nowotny 《Astrophysics and Space Science》1981,78(2):427-433
A direct approach of the dynamical equation for the evolution of the two-point density correlation function is given in an expanding flat Friedmann Universe in the Newtonian approximation. If the third and higher moments are neglected, a wave-like equation of third-order for the two-point density correlation function is found. The exact solution of this equation shows, in the large time limit, the usual Jeans instability t
4/3. It is suggested that the highern-point correlation function of the density grow liket
2n/3
in the same approximation. This indicates that every truncation procedure of the hierarchy of the equations is inapplicable at least for large timest. 相似文献
3.
Ekkehard Nowotny 《Astrophysics and Space Science》1984,103(2):249-270
On the basis of the hydrodynamical equations of a two-component gas (photons and hydrogen with coupling via Thomson scattering) in the recombination era of the Universe (standard model), the evolution of the density perturbations up to second order are calculated. It is shown, that the generated second-order amplitudes of the density fluctuations of the matter reach values of the same order as the first-order amplitudes within only one tenth of the expansion time for fluctuations with wavelengths corresponding to 107
M
. Upper limits in the density fluctuations (for the gravitationally instable modes) up to which first-order calculations are valid, are given. This calculation indicates that the linear perturbation analysis is very restricted, especially at wavelengths near the lower limit of the Jeans length.The linear analysis would be a good approximation only for density fluctuations of the matter with the density contrast less than 10–5–10–4 at the recombination era. Therefore, a nonlinear analysis which is not based on a perturbation series is required for studying the evolution of the density perturbations, because for this we need a density contrast of 10–2–10–3 at the end of the recombination era. 相似文献
4.
Josef Hron Walter Nowotny Rita Gautschy-Loidl Susanne Höfner 《Astrophysics and Space Science》2003,286(1-2):213-218
We present synthetic radii and visibilities in the IR, based on hydrostatic and dynamic model atmospheres of carbon stars.
The differences between these two sets of input models and to uniform disc models are discussed and compared to the expected
capabilities of the VLTI.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
A variety of new optical observations have been made over the bright core of the supermassiveHii region 30 Doradus and the ionized filamentary material surrounding this object. In addition, a more detailed analysis of previously published interstellar absorption andHi emission profiles has been undertaken.The velocity and density structure of this complex region is discussed and the new results analysed here shown to be compatible to the model of 30 Doradus presented in Cantóet al. (1980) and Meaburn (1980). 相似文献
6.
We discuss the variable degree of ionizationx of a hydrogen-helium plasma in the early Universe for a quasi-static expansion in thermal equilibrium. The final equation for the degree of ionization can be reduced to a polynomial of fourth order inx with known coefficients depending on the temperature. Restricting to a pure hydrogen-plasma applied to the recombination era, where the main ionization effects are due to photo-electric and collisional processes, we study the dynamical evolution of the degree of ionization for nonstatic and nonequilibrium situations. The calculation can be reduced to a pure quadrature. In the linear case, we also calculate the rate of ionization. 相似文献
7.
Ekkehard Nowotny 《Astrophysics and Space Science》1984,104(1):73-82
The formation and the evolution of shock waves in a two-component fluid during the recombination era of the Universe is studied. The fluid consists of photons and ionized hydrogen gas with interaction due to Thomson scattering. The analysis uses the expansion procedure in powers of the coordinates near the travelling wave front. Incorporating discontinuities in the first derivatives of the physical quantities, we are able to give the analytical solution which answers the questions as to when the discontinuities appear in the physical quantities themselves. Of the two possible waves (a radiation- and a matter-dominated wave) only the matter-dominated wave shows the shock phenomena. However, the shock is induced by the radiation due to Thomson scattering. Therefore, the time for the shock formation depends on the initial amplitude of the wave (as in usual shock phenomena) and on the collision frequency of the photons. 相似文献
8.
Ekkehard Nowotny 《Earth, Moon, and Planets》1979,21(3):257-274
The linear density and velocity perturbations are analyzed in a differentially rotating thin gravitating disc consisting of gas and dust. For the radial behaviour of the equilibrium density and the velocity of sound we assume a power law. The zeros of these perturbations have a distance behaviour like the distances of the planets and their satellites known as the Titius-Bode rule. It is suggested, that the knots of the velocity disturbances are the places where ring like dust accumulations occur. The mechanism is the same as in the Kundt's tube, where collisions between the dust and the oscillating gas are responsible for this effect. 相似文献
9.
Ekkehard Nowotny 《Astrophysics and Space Science》1981,76(1):235-254
Within the cosmological standard models of the Universe, we inquire the 2-fluid radiation hydrodynamics during and before the recombination era. If we neglect all nonlinearities with exception of those contained in the coupling term between the two fluids via the degree of ionization, there exists a strong feedback mechanism on the instable modes which prevents them from growing if their relative amplitudes of the density contrast have values in the order of 10–1–10–2. The non-linear equations are numerically solved by adiabatic elimination technique used usually in self-organization problems. The effect depends very on the redshift z and become maximum atz1350. It depends also on the masses involved for the rangeM>1011
M
. The lowest limits in the amplitudes (10–2) are imposed on the largest masses (1017
M
). In the range 106M/M
1011, the effect is independent of the mass. 相似文献
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