Galaxies are huge systems of stars and interstellar matter, usually with several million to trillion stars. Their masses are several million and trillion times that of the Sun, a range of a few thousands to several thousands of light years and are characteristically separated by millions of light years distance. One type of galaxy is an elliptical galaxy; these galaxies comprise about ten percent of all observed galaxies.
What are Characteristics of Elliptical Galaxies?
Elliptical galaxies are of an ellipsoidal shape and observation has suggested that they are typically triaxial, meaning they have three axes. The symmetrically arranged parts rotate around an imaginary line. Elliptical galaxies are large compilations of stars. The gravitational attraction between these stars leads to them remaining fairly close to each other.
Elliptical galaxies contain no defined rotation axis; this means stars in an elliptical galaxy have a broad range of orbital paths around the center galaxy. Despite this fact, the motions of the stars are not totally random. This consistency in the directions of the stars’ movements around the center establishes the general shape of the elliptical galaxy. In addition, photographs show elliptical galaxies to be redder in color than spiral galaxies. This fact is due to the majority of old stars found in elliptical galaxies. New stars are seen less frequently because elliptical galaxies contain a small amount of gas and dust; a fact which inhibits the formation of new stars.
Elliptical galaxies are found in a wider range of masses than spiral galaxies. The size of an elliptical galaxy can also vary greatly, with the smallest of elliptical galaxies being called dwarf ellipticals. Dwarf ellipticals might be just a small amount bigger than globular clusters, while giant elliptical galaxies can be some of the biggest galaxies in the Universe. Similarly, elliptical galaxies show a sizeable range in brightness. The brightest elliptical galaxy can be much brighter than the brightest spiral galaxy. In contrast, the dimmest elliptical galaxy can be much dimmer than the dimmest spiral galaxy.
How Are They Classified?
Elliptical galaxies range from things that are nearly spherical to those that are almost flat. The ones that are spherical are classified as E0 galaxies while the flattest are classified as E7. The ones that fall in between this spectrum are rated on a scale that ranges from numbers E1 to E6. Therefore, elliptical galaxies are classified as En, the n being filled in with a number correlating to whatever shape the galaxy may take.
The dilemma with the classification of these galaxies lies in the fact that it is reliant on the shape of the galaxy from our viewpoint. This does not therefore provide an accurate description of the true physical properties of the object. The only type in whose shape we can tell for sure would be an elliptical galaxy that is perfectly spherical. This is because other objects would appear different, depending from which angle the elliptical galaxy is observed, but a perfect sphere appears the same no matter which angle one examines it from.
By Lauren Culliton