Local Group

Definition

The Local Group is a small cluster of galaxies that includes the Milky Way Galaxy and the Andromeda Galaxy, along with about 50 other smaller galaxies. It is the closest major concentration of galaxies to the Milky Way and provides important insights into the structure and evolution of galaxies on a larger scale.

5 Must Know Facts For Your Next Test

1. The Local Group has a diameter of about 10 million light-years and contains over 54 known galaxies.
2. The two dominant galaxies in the Local Group are the Milky Way and the Andromeda Galaxy, which are on a collision course and will eventually merge.
3. The Local Group is part of the Virgo Supercluster, a larger structure that includes thousands of galaxies.
4. Studying the motions and interactions of galaxies within the Local Group provides insights into the distribution of dark matter and the formation of structure in the universe.
5. The presence of variable stars, such as Cepheid variables, in the Local Group galaxies has been crucial for measuring cosmic distances and understanding the expansion of the universe.

Review Questions

• Explain how the Local Group relates to the large-scale structure of the universe as described in Topic 1.7.
  • The Local Group is a small, gravitationally bound cluster of galaxies that is part of the larger Virgo Supercluster, which is one of the major structures in the observable universe. By studying the motions and interactions of galaxies within the Local Group, astronomers can gain insights into the distribution of matter, the effects of dark matter, and the formation of larger-scale structures in the universe. The Local Group provides a local laboratory for understanding the processes that shape the large-scale architecture of the cosmos.
• Describe how the presence of variable stars in Local Group galaxies, as discussed in Topic 19.3, has been crucial for measuring cosmic distances.
  • The Local Group contains a variety of variable stars, including Cepheid variables, that have been used as standard candles to measure the distances to other galaxies within the group. By comparing the observed brightness of these variable stars to their known intrinsic brightness, astronomers can calculate the distance to the host galaxy. This technique, known as the Cepheid distance ladder, has been instrumental in establishing the cosmic distance scale and understanding the expansion of the universe. The ability to accurately measure distances to Local Group galaxies has been a key factor in the development of our understanding of variable stars as cosmic distance indicators.
• Discuss how the architecture and distribution of galaxies within the Local Group, as described in Topics 25.1 and 28.3, provide insights into the formation and evolution of galaxies and large-scale structure in the universe.
  • The Local Group, with its two dominant spiral galaxies (the Milky Way and Andromeda) and numerous smaller dwarf galaxies, serves as a model for understanding the hierarchical formation and evolution of galaxies and their distribution in space. The observed interactions and mergers between galaxies within the Local Group, as well as the presence of dark matter, provide clues about the processes that shape the architecture of individual galaxies and the larger-scale structure of the universe. Additionally, the distribution of galaxies within the Local Group, and their motions relative to one another, offer insights into the underlying dark matter distribution and the formation of cosmic structure, as described in Topic 28.5. By studying the Local Group, astronomers can better understand the fundamental principles that govern the formation and evolution of galaxies and the large-scale structure of the universe.

Related terms

Milky Way Galaxy: The galaxy that contains our solar system and most of the stars visible in the night sky. It is a spiral galaxy that is part of the Local Group.

Andromeda Galaxy: The largest galaxy in the Local Group, a spiral galaxy located about 2.5 million light-years from the Milky Way.

Gravitational Lensing: The bending of light by the gravitational field of massive objects, which can be used to study the distribution of matter in the Local Group and beyond.