Ambipolar diffusion and core formation in molecular clouds

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:5150998

Lizano-Soberon, S

The author studies two dimensional axisymmetric models of the quasistatic formation of cloud cores inside a molecular cloud, due to ambipolar diffusion of the magnetic field. He then studies the core evolution with varying amounts of turbulent support, using periodic boundary conditions to represent the formation of molecular cloud cores in a much larger cloud, like the dense cores observed in NH{sub 3} in the Taurus molecular cloud by Myers and Benson (1983). He also defines a new critical mass M{sub cr} that includes all available mechanisms of support. A cloud will undergo dynamical gravitational collapse only if the mass M of the cloud is larger than this critical mass. Otherwise, it will evolve quasistatically by ambipolar diffusion of the magnetic field. There are, then, three interesting regimes for star formation: (a) If the cloud is supercritical M/M{sub cr} > 1, gravity can overwhelm all available means of support and the cloud will collapse and possibly fragment into many pieces. If the cloud is subcritical M/M{sub cr} < 1, it will evolve quaistatically as the magnetic field is lost by ambipolar diffusion. Then, small cores will condense from the background and (b) if the core is subumbral, a more condense equilibrium state will be reached with straight field lines and star formation cannot occur. But, (c) if the core is superumbral, there is no equilibrium available and a gravitational runaway will eventually occur: these cores will become dense ammonia cores and finally a low mass star will be formed in the center.

• Research Organization: California Univ., Berkeley, CA (USA)
• OSTI ID: 5150998
• Country of Publication: United States
• Language: English

Related Subjects

640102 -- Astrophysics &amp; Cosmology-- Stars &amp; Quasi-Stellar
Radio &amp; X-Ray Sources
640105* -- Astrophysics &amp; Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AMBIPOLAR DIFFUSION
AMMONIA
BOUNDARY CONDITIONS
COSMIC GASES
DIFFUSION
FLUIDS
GASES
HYDRIDES
HYDROGEN COMPOUNDS
INTERSTELLAR MAGNETIC FIELDS
INTERSTELLAR SPACE
MAGNETIC FIELDS
MASS
MATHEMATICAL MODELS
MOLECULES
MORPHOLOGY
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
PROTOSTARS
SPACE
STAR CLUSTERS
STAR EVOLUTION
TURBULENCE