sentences:  Noah Brosch and colleagues showed that the luminous ring lies at the inner edge of a much larger neutral hydrogen ring.Even though Hoag's Object was clearly shown on the Palomar Star Survey, it was not included in either the "Morphological Catalogue of Galaxies", the "Catalogue of Galaxies and Clusters of Galaxies", or the "catalogue of galactic planetary nebulae".In the initial announcement of his discovery, Hoag proposed the hypothesis that the visible ring was a product of gravitational lensing.