Joseph Boussinesq and his approximation: a contemporary view

We investigated spherically symmetric solution for nonrelativistic cosmological fluid equations and thermodynamic equation of state for Newtonian stars. It was shown that the assumption of a polytropic equation, , at the center of the star only suffices to integrate the equations explicitly. Our exact solution yields many fruitful results such as stellar stability, spherical oscillation and collapses of stars. Pressure, temperature, and density profiles inside stars were obtained. Central densities, pressures and temperatures of the Newtonian stars such as Sun, Jupiter and Saturn were also calculated. Collapse and expansion mechanism was explained by the heat transfer mechanism inside star. The upper bound value of white dwarf mass obtained by the Newtonian cosmological fluid equations turns out to be comparable to the static limit of Chandrasekhar one. Motion of the Universe was also discussed within the framework of Newtonian mechanics. Our calculation results without considering nuclear reactions insid...

Hydrodynamics and Thermodynamics of Newtonian Stars

A brief introduction on the importance of interstellar molecules - for energy transport and as probes - is given, followed by discussions of selected high angular resolution results on initial conditions for stellar formation (i) in nearby, cold dark clouds (low mass stars) (ii) in warmer, denser giant molecular clouds (also massive stars), and (iii) in nearby galaxies (large scale density wave triggering of cloud/star formation)

Recent Onsala Observations Related to Star Formation

We present observations, which are part of an ongoing investigation, of the CO (J=1-0) emission in the spiral galaxy M51. The spectra were obtained in a beamswitched on-on mode with the Onsala 20 m antenna (beam size ∿33″), equipped with a cooled mixer and a 512·1 MHz multichannel receiver, and are shown in Figure 1. The inset diagram shows the observed positions superposed on the optical outline of the galaxy. With the present signal-to-noise ratio there is no evidence for an arm-interarm intensity contrast. This is even more apparent in integrated intensity. This result agrees with the lower resolution findings of Rickard et al. (1981). We have observed 13CO in one position (22″ south of the center). The 13CO to 12CO ratio, ∿0.1, agrees with Bell results from observations with a 1!7 beam (Encrenaz et al. {dy1979}).

CO Observations of M51

Correlation of the direct observation results about fluid-dynamic properties of the galaxy

Galaxies are examined through their primary components of gas and stars. The normal spiral and barred spiral galaxies have gaseous and stellar constituents in a thin disk, with a prominent nuclear bulge in the inner parts. The gaseous disk of matter is considered as a large-scale motion of the interstellar medium in the presence of the collective gravitational field of the massive stellar component in normal and spiral galaxies. The stellar component is viewed from a fluid-dynamical perspective; finally the asymptotic theory, dynamical mechanisms, and modal maintenance are discussed.

W. W. Roberts

Papers

Some Fluid-Dynamical Problems in Galaxies