What Warped Disks Can Tell Us about Galaxy Halos and Gravity

A warp on the outer fringe of a galaxy is often thought to signal time-dependent settling of gas into a preferred plane of that galaxy. As settling occurs, a twist should be apparent in the region of the warped gas layer. The direction of the twist - prograde or retrograde with respect to the direction of the disk rotation - should identify whether the gas is settling into an oblatelike potential well or into a prolatelike potential well. A study of twisted warps in a large number of spiral galaxies should show whether dark halos are as diverse in geometric shape as are elliptical galaxies. Furthermore, evidence for even a few disks residing in prolatelike potential wells would probably rule out theoretical models that have attempted to explain flat rotation curves by modifying gravity or the dynamics of gravitating systems, because these theoretical models demand that all disk galaxies exhibit oblatelike potential wells.