Elliptical galaxies - Definition

An elliptical galaxy is a type of galaxy in the Hubble sequence characterized by the following physical properties:

The giant elliptical galaxy NGC 4881 (the spherical glow at upper left) lies at the edge of the Coma Cluster of Galaxies.

• No or at most inconsiderable amount of angular momentum.
• No or at most inconsiderable amount of interstellar matter, no young stars, no open star clusters
• Consisted of old, so-called Population II stars
• Larger elliptical galaxies typically have a system of globular clusters

This traditional portrait of elliptical galaxies paints them as galaxies where the star formation was over after the initial burst, now shining only with their aging stars. No significant evolution was thought to happen.

Some recent observations have found young, blue star clusters inside a few elliptical galaxies, along with other structures that can be explained by galaxy mergers. In the new vision (still quite experimental), an elliptical galaxy is the result of a long process where one or more smaller galaxies, of any type, collide and fuse in a larger one.

This fusion process may at time carry on until recent or contemporary ages, and is not limited to giant ellipticals. For example, our own Milky Way is known to be "digesting" a couple of small galaxies right now.

External links

• Elliptical Galaxies (http://www.seds.org/messier/elli.html), SEDS Messier pages