Facts on Elliptical Galaxies

Appearance

• The Goddard Space Flight Center website states the appearance of elliptical galaxies is dependent upon how quickly the stars were formed. The slow development of stars from gases and dust results in a spiral galaxy with distinctive arms. However, astronomers believe that when two galaxies merge or collide, matter is thrown out and the remaining stars maintain their random orbits, forming an elliptical galaxy with little or no radial motion.

Features

• Most elliptical galaxies contain older, low-mass stars and little interstellar matter like gas or dust. Consequently, ellipticals have little or no star formation. Elliptical galaxies come in giant (gE) and dwarf varieties (dE). Giant ellipticals can be 50 times the diameter of dwarf ellipticals and more than 20,000 times brighter, according to \"1001 Things Everyone Should Know About the Universe.\" Surrounded by large globular clusters, elliptical galaxies make up 60 percent of all galaxies within several hundred million light years of Earth, with the majority being dwarf ellipticals.

Types

• According to Cornell University, the largest galaxies in the universe are giant ellipticals (gE), which can contain more than a trillion stars and span over two million light years. Elliptical galaxies also constitute the smallest galaxies in the universe. These dwarf galaxies (dE) are extremely faint, often found in galaxy clusters or near large spiral galaxies. Our Milky Way, for example, contains nine dwarf ellipticals. ??

Luminosity

• The light from an elliptical galaxy is brighter in the center and gradually becomes fainter toward the outer regions. Since elliptical galaxies consist of older stars, they appear redder on the inside than on the outside. Large ellipticals tend to be redder than smaller ellipticals and have greater absorption features. Larger absorption features correlate with larger UV excess, and in turn, contain fewer planetary nebulae.

Speculation

• For many years, astronomers have studied and observed massive rotating black holes in the center of giant elliptical galaxies. These gE galaxies emit high-energy, radioactive particles in the form of radio waves, but their true nature remains unclear, according to the Science and Technology Review. The giant elliptical galaxy NGC 4261, for example, is one of the brightest galaxies in the Virgo cluster. Hubble Space Telescope images show NGC 4261 as a giant disk containing billions of stars, with two radio-wave jets emanating from its center--possibly fueling a black hole.