Noah Brosch suggested that Hoag's object might be a product of an extreme "bar instability" which occurred a few billion years ago in a barred spiral galaxy. Schweizer "et al" claims that this is unlikely because the nucleus of the object is spheroidal, whereas the nucleus of a barred spiral galaxy is disc-shaped. However, evidence is somewhat thin for this dispute to be settled. A few other galaxies share the characteristics of Hoag's object, including the bright detached ring of stars, but their centers are elongated or barred, and they may exhibit some spiral structure While none match Hoag's object in symmetry, this handful of galaxies are known to some as Hoag-type galaxies.