Gravitational instabilities in shearing, magnetic galaxies with a cloudy interstellar gas

Journal Article · Sat Jul 01 04:00:00 EDT 1989 · Astrophysical Journal; (USA)

DOI:https://doi.org/10.1086/185486· OSTI ID:5509181

Elmegreen, B G ^[1]

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1. IBM Thomas J. Watson Research Center, Yorktown Heights, NY (USA)

A cloudy ISM in a galactic disk with rotation, shear, and an azimuthal magnetic field is found to be gravitationally unstable on all length scales down to the cloud-collision mean-free path. Most instabilities are not transient, but grow exponentially without limit. The magnetic field overcomes the Coriolis force, and the dissipation from cloud collisions effectively removes the pressure.The collapse occurs at about the conventional Jeans rate for masses between 1000 and 10 million solar masses. If the probability for collapse on a particular scale is proportional to the collapse rate on that scale, then an M exp -1.5 mass spectrum results. Gravitational instabilities should occur continuously in the ambient medium, and have an enhanced rate in spiral density-wave crests and swept-up shells. They readily account for the formation of most self-gravitating clouds in spiral galaxies and could be the single most important event that initiates star formation. 8 refs.

• OSTI ID: 5509181
• Journal Information: Astrophysical Journal; (USA), Journal Name: Astrophysical Journal; (USA) Vol. 342; ISSN ASJOA; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CORIOLIS FORCE
COSMIC GASES
FLUIDS
GALAXIES
GASES
GRAVITATIONAL COLLAPSE
GRAVITATIONAL INSTABILITY
INSTABILITY
INTERSTELLAR MAGNETIC FIELDS
INTERSTELLAR SPACE
MAGNETIC FIELDS
PERTURBATION THEORY
PLASMA INSTABILITY
SHOCK WAVES
SPACE
STAR EVOLUTION