Elliptical galaxies

Definition

Elliptical galaxies are a type of galaxy characterized by their smooth, featureless light distribution and elliptical shapes, ranging from nearly spherical to elongated forms. They typically contain older, red stars and have little to no ongoing star formation, making them distinct from spiral galaxies. The formation of elliptical galaxies is often linked to galaxy mergers and interactions, where two or more galaxies collide and merge, leading to a more uniform stellar population.

5 Must Know Facts For Your Next Test

1. Elliptical galaxies are classified as E0 to E7 on the Hubble Sequence, with E0 being nearly spherical and E7 being highly elongated.
2. They contain very little interstellar gas and dust compared to spiral galaxies, which contributes to their low rates of star formation.
3. Most massive elliptical galaxies are found in the centers of galaxy clusters and can contain trillions of stars.
4. Elliptical galaxies often form as a result of major mergers between spiral galaxies, leading to the redistribution of stars and the cessation of new star formation.
5. They are believed to be the end result of galactic evolution, where interactions and mergers lead to larger, more stable structures over time.

Review Questions

• How do elliptical galaxies differ in structure and composition compared to spiral galaxies?
  • Elliptical galaxies differ from spiral galaxies primarily in their structure and composition. While spiral galaxies have well-defined arms and a significant amount of interstellar gas and dust that fuels ongoing star formation, elliptical galaxies are more rounded and lack these features. They generally consist of older stars with little to no new star formation occurring due to the absence of gas and dust. This results in a more uniform light distribution without the prominent structures seen in spirals.
• Discuss the role of galaxy mergers in the formation of elliptical galaxies and their impact on stellar populations.
  • Galaxy mergers play a crucial role in the formation of elliptical galaxies by combining multiple galactic systems into one. During these mergers, gravitational interactions cause the stellar populations from the merging galaxies to redistribute throughout the newly formed galaxy. As a result, elliptical galaxies often exhibit a mixed stellar population that is primarily older and redder, reflecting the end stages of star formation. This process can also lead to a decrease in star formation activity as gas is consumed or expelled during the merger.
• Evaluate the significance of understanding elliptical galaxies in the broader context of galactic evolution and cosmology.
  • Understanding elliptical galaxies is significant for several reasons in the context of galactic evolution and cosmology. They provide insights into how galaxies evolve through interactions and mergers over cosmic timescales, revealing the dynamics behind galaxy formation. Studying their properties helps astronomers trace back the history of galaxy clusters and gain a better understanding of dark matter's role in shaping large-scale structures. Additionally, because they represent an end stage in galactic evolution, examining elliptical galaxies can help predict future evolutionary pathways for other types of galaxies in our universe.

Related terms

Galaxy Merger: A galaxy merger occurs when two or more galaxies collide and combine their mass, often resulting in the formation of an elliptical galaxy.

Star Formation Rate: The star formation rate measures how many new stars are formed in a galaxy over a specific time period, which is typically low in elliptical galaxies.

Hubble Sequence: The Hubble Sequence is a classification scheme for galaxies, categorizing them into different types such as spiral, elliptical, and irregular based on their morphology.