Cosmic Gas Dynamics

a branch of astrophysics that studies the motion of gaseous masses under cosmic conditions using the methods of gas dynamics. It became an independent branch in the 1940’s. Cosmic gas dynamics is used in investigations of motion in the atmosphere of the sun and stars, in inter-stellar gas, in solar and stellar winds, and in the metagalactic medium. The most characteristic phenomenon of gas dynamics is the shock wave. Shock waves are generated in the solar atmo-sphere by chromospheric flares; on passing through the corona, the waves generate bursts of radiation and, on reaching the earth, create magnetic storms and related geophysical phenomena. Strong shock waves are generated in the interstellar medium by the expanding shells of novae and supernovae. They are apparently also generated by galaxies moving through the intergalactic medium.

The specific features of shock waves and other phenomena of gas dynamics under cosmic conditions are governed by the fact that the cosmic medium is a partially ionized gas, or plasma. Owing to the large difference between the masses of electrons and ions, the electronic heat conductivity predominates in cosmic space. The heat wave, generated by a shock wave, overtakes the shock-wave front and the gas ahead of the front is heated up, which affects the properties of the wave. The motion of the particles of the ionized gas is significantly affected by magnetic fields; in particular, it restricts the mean free path of particles across lines of force of the magnetic field, thus reducing the heat conductivity in this direction. The field generates pressure, which is added to the pressure of the gas. Of great importance in the plasma is the collective interaction of particles with fields rather than with separate particles, the fields being generated by the totality of motion of a large number of such particles. This determines the specific nature of cosmic gas dynamics.

Studies in cosmic gas dynamics are conducted in the USSR at the Institute of Physics of the Academy of Sciences of the USSR, the P. K. Shternberg State Institute of Astronomy, the Institute of Applied Mathematics of the Academy of Sciences of the USSR, the Scientific Research Institute of Radiophysics of the University of Gorky, and other astronomical and physical establishments. Articles on these subjects are published in the journals Astronomicheskii zhurnal and Astrofizika (USSR) and in Astro-physical Journal (USA), Cosmic Electrodynamics (an international journal), and other periodicals.