I wasn't certain if this topic strictly belonged in the GR forum. I have read the article 'Singular disk of matter in the Cooperstock-Tieu galaxy model', by Mikolaj Korzynski (http://arxiv.org/abs/astro-ph/0508377). In it, the author finds that the singularity within Cooperstock & Tieu's model is not coordinate based. What I don't understand is why the author takes the liberty of calling the solution questionable, when completely unphysical singularities of other types are clearly acceptable. ex: Cosmic strings being 1D singular filaments, and black holes being 3D singular spheres. Does anyone know of any reason to consider 2D singularities any less reasonable than 1D or 3D singularities? Am I misinterpreting the author's use of the phrase "the model of galaxy they propose is questionable"? Thanks for any insight.