Nonhomologous contraction and equilibria of self-gravitating, magnetic interstellar clouds embedded in an intercloud medium: Star formation. II. Results

Journal Article · Thu Jul 01 00:00:00 EDT 1976 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/154478· OSTI ID:7175638

Mouschovias, T C

We present models representing the nonhomologous contraction and equilibria of isothermal, self-gravitating interstellar clouds bounded by the pressure of a hot and tenuous intercloud medium. A frozen-in interstellar magnetic field threads both media. It invariably causes a self-gravitating cloud to become oblate with its major axis normal to the field lines. The flattening increases with the strength of the magnetic field, or with stronger gravitational forces, or with increasing intercloud pressure: other quantities remainig fixed in each case. A ratio of gas densities at the center and at the surface exceeding the Bonor-Ebert critical value (=14.3) can easily be obtained while the cloud is still at equilibrium. For a fixed mass-to-flux ratio, an increasing intercloud pressure eventually leads to gravitational collapse. A cloud of uniform density threaded by a uniform magnetic field and surrounded by an intercloud medium of fixed pressure can reach equilibrium only if its radius does not exceed a critical value; otherwise collapse ensues.We determine the slope kappa of the (log B, log p)-curve at the center of a cloud. It is certainly less than its isotropic-contraction value (2/3) with a likely range 1/3< or =kappa< or =1/2. (No theoretical lower limit exists; it must be set by observations.) This implies that milligauss fields can be found only in regions of gas density approximately-greater-than10/sup 6/ cm/sup -3/, unlike current notions of 10/sup 4.5/ cm/sup -3/.Finally, we show that neither an O5 star nor a supernova explosion can disperse a dense, massive cloud. Hence, the observed inefficiency of the star formation process must have other causes. We suggest the magnetic field as such a cause; it may hold the collapse of the outlying portions of a cloud. This necessitates a sequence of events leading to star formation qualitatively different from current ideas. (AIP)

• Research Organization: Physics Department, University of California, Berkeley
• OSTI ID: 7175638
• Journal Information: Astrophys. J.; (United States), Vol. 207:1
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
INTERSTELLAR SPACE
INTERSTELLAR MAGNETIC FIELDS
STAR EVOLUTION
STAR ACCRETION
CONTRACTION
COSMIC DUST
COSMIC GASES
EQUILIBRIUM
GRAVITATION
HYDROMAGNETIC WAVES
PLASMA
ZEEMAN EFFECT
DUSTS
FLUIDS
GASES
MAGNETIC FIELDS
SPACE
640105* - Astrophysics &amp; Cosmology- Galaxies