Gravitational Collapse of Filamentary Clouds

Details Gravitational Collapse of Filamentary Clouds Gravitational Collapse of Filamentary Clouds

Dec 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998pasj...50..577k&link_type=abstract

Publications of the Astronomical Society of Japan, v.50, p.577-586.

Astronomy and Astrophysics

Astronomy

10

Gravitation, Hydrodynamics, Interstellar: Clouds, Stars: Formation

Scientific paper

We consider gravitational collapse of a filamentary cloud under the assumption that it is axisymmetric and uniform along the axis. The pressure is approximated by a polytrope of P = K \rho ^\gamma. We found a similarity solution for the collapse when the polytropic index lies in the range 0 < \gamma < 1 . According to the similarity solution, the collapse consits of two phases. In the first phase the filament becomes denser and thiner. The density at the center ( rho _c ) increases in proportion to (t _0 - t) ^{-2} , where t _0 denotes the epoch at the end of the first phase. Meanwhile, the filament diameter (FWHM) decreases in proportion to (t _0 - t) ^{(2 - \gamma)} The line density of the central filament of \rho > 0.1 \rho c vanishes at t = t_0 , since it is proportional to the central density and the square of the diameter lbrack ~ (t _0 - t) ({2) (1 - gamma )} rbrack . In the second phase the central filament grows in mass by accretion. The collapse in the second phase is similar to the inside-out collapse of a spherical gas cloud. When the polytropic index gamma is closer to unity, the collapse is slower. When \gamma = 0.999 , the collapse is 12-times slower than the dynamical one. We also found from numerical simulations having various initial conditions that the collapse of a filamentary cloud approaches asymptotically the similarity solution irrespectively of the initial condition.

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