Chapter IV Thermal Instability in the Expanding Universe

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In the expanding universe, the thermal instability, if it occurs, can develop much more quickly than the gravitational instability and, therefore, may provide a possible mechanism to initiate the formation of galaxies. The general characteristics of thermal instability are discussed for non-equilibrium media with due regard to the ionization change and the optical depth effect of fluctuations. If the matter can be brought to a temperature high enough to ionize hydrogen after 10^7 years of the cosmic age, the energy loss from the matter becomes mainly due to the bound-free processes rather than the Compton scattering and the thermal instability will be set up. Such a high temperature (〜10^4゜K) is excluded in the thermal history of the expanding universe even if the effect of hydrodynamic turbulence is taken into account, since the inverse Compton loss it extremely large just after the epoch of the recombination of hydrogen when the turbulence decays rather rapidly. There is, however, a possibility that the turbulent energy is stored in the magnetic field and in cosmicray particles at the epoch of hydrogen recombination and released later (〜10^7 years) when the inverse Compton loss becomes less efficient.
理論物理学刊行会の論文
1972-02-29