We examine the idea that observed galactic warps may represent discrete modes of bending in a self-gravitating disc. If the disc is subject to the potential of a flattened unseen halo, then discrete modes may exist which are not sensitive to details of the disc edge; the most important parameter is the core radius of the halo. We discuss the variety of warp shapes which can arise in the presence of an oblate dark halo, construct models for two observed warps, and consider how warps may be used to constrain the distribution of unseen matter in galaxies. Isolated discs may also have discrete modes of bending, but only when the density falls to zero over quite a narrow region at the edge; these modes are probably not relevant to the interpretation of observed warps.
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Sparke et al. (1988) studied this question.