Spiral galaxy

Definition

A spiral galaxy is a type of galaxy characterized by its distinct spiral arms that wind outwards from the center, creating a flat, rotating disk. These galaxies often contain a mix of young and old stars, along with gas and dust, which contribute to star formation in the arms. The structure of spiral galaxies plays an important role in the overall architecture of the universe and is a key aspect of understanding how galaxies, stars, and planets are organized.

5 Must Know Facts For Your Next Test

1. Spiral galaxies are one of the most common types of galaxies in the universe, with famous examples including the Milky Way and the Andromeda Galaxy.
2. The arms of spiral galaxies are sites of ongoing star formation, containing young, hot stars that give off bright light, while the central bulge often contains older stars.
3. Spiral galaxies can be classified based on the tightness of their arms and the size of their central bulge, which can vary widely among different spiral galaxies.
4. The rotation of a spiral galaxy affects its shape, with the gravitational forces at play causing the arms to be clearly defined while other regions may be less structured.
5. Interactions with other galaxies can trigger new star formation in spiral galaxies and even lead to morphological changes such as transforming into barred spirals.

Review Questions

• How do the structures of spiral galaxies differ from those of elliptical galaxies in terms of star formation and composition?
  • Spiral galaxies have a distinct structure with well-defined arms that are rich in gas and dust, making them active sites for star formation. In contrast, elliptical galaxies tend to lack these structures and contain mostly older stars with little interstellar gas or dust, resulting in minimal new star formation. This fundamental difference in composition and activity highlights the dynamic nature of spiral galaxies compared to the more static nature of elliptical ones.
• Discuss the significance of spiral arms in spiral galaxies and their role in star formation.
  • The spiral arms in spiral galaxies are crucial for star formation as they contain a higher density of gas and dust compared to other regions. The gravitational forces within these arms compress gas clouds, leading to increased density which triggers nuclear fusion processes that give rise to new stars. This ongoing star formation contributes to the vibrant luminosity seen in many spiral galaxies, showcasing their active nature within the universe.
• Evaluate the impact of interactions between spiral galaxies on their evolution and structural changes.
  • Interactions between spiral galaxies can significantly influence their evolution by triggering bursts of star formation and altering their structures. When two spiral galaxies collide or come close to each other, their gravitational forces can distort their shapes, often leading to features like tidal tails or new bar structures. Such interactions can also lead to mergers that transform one or both galaxies into different types, illustrating how dynamic processes shape the fate of these cosmic entities over time.

Related terms

Elliptical galaxy: A type of galaxy that is rounded or elliptical in shape and lacks the distinct spiral structure found in spiral galaxies, often containing older stars and little interstellar gas.

Barred spiral galaxy: A variant of spiral galaxies that have a central bar-shaped structure composed of stars, with spiral arms extending from the ends of the bar.

Galaxy cluster: A large group of galaxies bound together by gravity, which can include various types of galaxies such as spiral, elliptical, and irregular galaxies.