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Session 24 - Disks, Bars & Halos.
Oral session, Wednesday, January 07
International Ballroom East,
We have identified a previously unknown preferred plane orientation for gaseous disks in oblate spheroidal gravitational potential wells such as the dark matter halos of galaxies. Three-dimensional numerical hydrodynamic simulations show that, even when the self-gravity of the gas is ignored, gas can settle into a steady-state disk configuration that is inclined to the equatorial plane of the halo. In steady-state, the gas moves in nonprecessing, elliptical orbits, hence the disk is not disrupted by differential precession. (A corresponding analytical model for such a steady-state disk configuration also has been derived for potential wells that deviate only slightly from a perfect sphere.) Gas in this steady-state flow experiences periodic phases of compression and rarefaction during each orbit, which could naturally promote a steady rate of star formation. However, stars that are formed in such an inclined disk of gas will not occupy periodic orbits. Differential precession of stellar orbits should ultimately create a stellar ``disk'' that is thicker than, but surrounds, the gaseous disk from which the stars formed.
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Program listing for Wednesday