Dynamics of a Rotating Gaseous Ellipsoid in an Expanding Universe

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In order to assess the importance of the coupling of vorticity with the cosmic expansion in the process of galaxy formation, dynamical equations for a rotating gaseous ellipsoid with uniform density embedded in an expanding universe are derived on the basis of our Newtonian hydrodynamical equations rewritten so as to be useful in a rotating frame of reference relative to the cosmological one. Numerical integrations of the equations are carried out on gaseous ellipsoids of the initial density ρ=1.2_<ρB>, 1.1_<ρB> and 1.05_<ρB>, where _<ρB> is the background density of the expanding universe. It is numerically shown that the ellipsoid becomes free from the expansion effects and starts to collapse when ρ/_<ρB> attains the values of 5.4 to 5.6, depending on the configuration of the ellipsoid. The initial non-axisymmetric structure is amplified in the course of the gravitational collapse and finally reaches an infinitely thin elliptical disk. When the angular momentum is large, the gravitationally bound system cannot be established within 10^<10> years. If the disk galaxy is formed from an initial density fluctuation with sufficient angular momentum, the initial velocities must be rather smaller than the general expanding velocity, otherwise the density fluctuation cannot rapidly become a gravitationally bound system in the plane perpendicular to the angular momentum vector. If this mechanism is correct, it would be indicative of the presence of primordial strong turbulence in the expanding universe.
理論物理学刊行会の論文
1972-01-25

Dynamics of a Rotating Gaseous Ellipsoid in an Expanding Universe

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