Elliptical Galaxies

Overview

Elliptical galaxies are one of the three main types of galaxies, along with spiral galaxies and irregular galaxies. They are characterized by their smooth, featureless appearance and lack of spiral arms. Elliptical galaxies are composed mainly of old stars, and they are typically found in galaxy clusters.

Formation

Elliptical galaxies are thought to form through the merger of smaller galaxies, which results in the redistribution of stars and the loss of angular momentum. This process leads to the formation of a spheroidal, ellipsoidal structure without distinct spiral arms.

Classification

Elliptical galaxies are classified based on their shape, ranging from E0 (nearly spherical) to E7 (highly elongated). The classification is based on the ratio of the major axis to the minor axis of the galaxy's apparent elliptical shape.

Physical Properties

Elliptical galaxies are predominantly composed of older stars, with little ongoing star formation. They also contain very little interstellar gas and dust compared to spiral galaxies. Elliptical galaxies tend to have higher stellar velocity dispersions, indicating a more chaotic and less organized motion of stars within them.

Study Guide

1. Describe the appearance of an elliptical galaxy and explain how it differs from a spiral galaxy.
2. Explain the formation process of elliptical galaxies, including the role of galaxy mergers.
3. Discuss the classification system for elliptical galaxies and how it relates to their shape.
4. Compare the stellar populations and interstellar content of elliptical and spiral galaxies.
5. Investigate the physical properties of elliptical galaxies, such as stellar velocity dispersion and luminosity.