has since been queried due to the existence of extremely isolated, low-luminosity lenticular galaxies such as LEDA 2108986. Faded spirals The absence of gas, presence of dust, lack of recent star formation, and rotational support are all attributes one might expect of a spiral galaxy which had used up all of its gas in the formation of stars. This possibility is further enhanced by the existence of gas poor, or "anemic," spiral galaxies. If the spiral pattern then dissipated the resulting galaxy would be similar to many lenticulars. Moore et al. also document that tidal harassment - the gravitational effects from other, near-by galaxies - could aid this process in dense regions. The clearest support for this theory, however, is their adherence to slightly shifted version of Tully–Fisher relation, discussed above. A 2012 paper that suggests a new classification system, first proposed by the Canadian astronomer Sidney van den Bergh, for lenticular and dwarf spheroidal galaxies (S0a-S0b-S0c-dSph) that parallels the Hubble sequence for spirals and irregulars (Sa-Sb-Sc-Im) reinforces this idea showing how the spiral–irregular sequence is very similar to this new one for lenticulars and dwarf ellipticals. Mergers The analyses of Burstein and Sandage showed that lenticular galaxies typically have surface brightness much greater than other spiral classes. It is also thought that lenticular galaxies exhibit a larger bulge-to-disk ratio than spiral galaxies and this may be inconsistent with simple fading from a spiral. If S0s were formed by mergers of other spirals these observations would be fitting and it would also account for the increased frequency of globular clusters. It should be mentioned, however, that advanced models of the central bulge which include both a general Sersic profile and bar indicate a smaller bulge, and thus a lessened inconsistency. Mergers are also unable to account for the offset from the Tully–Fisher relation without assuming that the merged galaxies were quite different from those we see today. Disk growth via accretion The creation of disks in, at least some, lenticular galaxies via the accretion of gas, and small galaxies, around a pre-existing spheroidal structure was first suggested as an explanation to match the high-redshift compact massive spheroidal-shaped galaxies with the equally compact massive bulges seen in nearby massive lenticular galaxies. In a "downsizing" scenario, bigger lenticular galaxies may have been built first - in a younger universe when more gas was available - and the lower-mass galaxies may have been