Even though spiral galaxies and irregulars differ sometimes enormously from each other, they have a fairly recognizable configuration and basic pattern. Elliptical galaxies, on the other hand, can vary in shape from a seemingly perfect sphere to a squashed globe. Despite their rounded shapes, most ellipticals do not rotate; and even those which do spin revolve far slower than most spirals.
Photo. The M87 elliptical galaxy is particularly interesting because Hubble spotted a black hole in the galaxy. Courtesy of Carina Software, 12919 Alcosta Boulevard, Suite #7, San Ramon, CA 94583, (510) 355-1266. Used with permission.
Ellipticals appear to glow because the light from their bright cores fades as it reaches the dim outer regions of the galaxies. For the most part, these galaxies contain very little dust and only tiny amounts of gases, so their light radiates uninhibited by small, scattered particles.
Photo. The NGC 4881 galaxy is one of many galaxies in the gigantic Coma Cluster of galaxies. Courtesy NASA, Hubble Space Telescope WFPC Team, Code 170-25, Caltech Pasadena, CA 91125.
Their virtually dust-free environments allow these galaxies to shine clearly, but the lack of gas means that no new stars are formed in ellipticals. Though new stars are found only in spiral and irregular galaxies, elliptical galaxies are exceedingly more plentiful than their spinning, star-producing spiral counterparts.
Astronomers do believe, however, that several million stars are exploding in at least one elliptical galaxy, Centaurus A, and are spewing out clouds of gas and dust. The full implications of the explosions are not clear because the thick ring formed by the remnants of the stars is blocking our view of the galaxy's center.
