The gravitational instability of collisionless particles in a cosmological self-similar shell

Details The gravitational instability of collisionless particles in a cosmological self-similar shell The gravitational instability of collisionless particles in a cosmological self-similar shell

Nov 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989apj...346...12h&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 346, Nov. 1, 1989, p. 12-27. Research supported by the Robert A. Welch Foun

Statistics

Computation

7

Computational Astrophysics, Cosmology, Galactic Clusters, Gravitational Effects, Galactic Evolution, Perturbation Theory, Universe

Scientific paper

A flat Friedmann-Robertson-Walker (FRW) model has been used to study the nature of gravitationally unstable linear modes of an expanding, self-similar, spherical shell made of cold collisionless particles. Dimensionless growth rates of the fundamental radial modes were calculated as a function of the spherical eigennumber l, and compared with previous calculations of linear stability in the thin shell approximation. Two major differences were observed: first, the growth rates for small l were significantly smaller in this case, although it remains true that even l = 1 modes are gravitationally unstable. Second, the dimensionless growth rate grows with logarithmic dependence on l when l is very large. The latter result is partly due to the fact that the collisionless particles have no nonradial motions, and partly due to the long-range nature of gravitational interactions. It is found that the spherical shell is unstable on all scales. Consequently, a generic positive energy perturbation in a cold self-gravitating medium will not evolve into a spherical configuration. The effects of including a finite thermal velocity dispersion and the astrophysical implications of the results are discussed.

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