The Ghostliest Galaxies; Magnificent Cosmos; Scientific American Presents; by Bothun; 4 Page(s)
Astronomers have known for decades that galaxies exist in three basic types: elliptical, spiral and irregular. The ellipticals are spheroidal, with highest light intensity at their centers. Spirals, which include our own Milky Way, have a pronounced bulge at their center, which is much like a mini-elliptical galaxy. Surrounding this bulge is a spiral-patterned disk populated with younger, bluish stars. And irregular galaxies have relatively low mass and, as their name implies, fit none of the other categories.
With only minor refinements, this system of galactic classification has changed little since astronomer Edwin Hubble originated it some 70 years ago. Technological advances, however, have significantly improved astronomers' ability to find objects outside the Milky Way galaxy that are extraordinarily hard to detect. Over the past decade my colleagues and I have used an ingenious method of photographic contrast enhancement invented by astronomer David J. Malin of the Anglo-Australian Observatory, as well as electronic imaging systems based on improved charge-coupled devices (CCDs).