How do galaxies form and evolve?

Galaxy formation and evolution is a complex process that involves several key factors, including gravity, dark matter, and mergers. Here’s a detailed overview of how galaxies form and evolve:

1. Initial Formation:
   • Quantum Fluctuations: The process begins with tiny quantum fluctuations in the aftermath of the Big Bang, which lead to slight variations in the density of the universe[2][3].
   • **Gravitational Collapse variations cause gas clouds to collapse under gravity, forming the first high-mass stars and proto-galactic structures[1][3].
   • Dark Matter: Dark matter plays a crucial role in this process, providing the gravitational scaffolding that allows normal matter to clump together and form galaxies[2][5].
2. Hierarchical Clustering:
   • Bottom-Up Model: The most widely accepted model is the hierarchical or bottom-up model, where small galaxies form first and then merge to form larger ones[1][3].
   • Mergers: These mergers are driven by gravitational interactions and are essential for the growth and evolution of galaxies[1][4].
3. Galaxy Evolution:
   • Spiral and Elliptical Galaxies: Spiral galaxies form through the collapse of gas clouds and can evolve into elliptical galaxies through mergers. Elliptical galaxies are more common in crowded regions of the universe and are often the result of major mergers[2][4].
   • Star Formation: Star formation is influenced by the availability of cold gas and can be triggered by mergers and interactions between galaxies[2][4].
   • Black Holes: Supermassive black holes at the centers of galaxies play a significant role in their evolution, influencing star formation and gas cooling[2][4].
4. Ongoing Processes:
   • Galactic Cannibalism: Larger galaxies can absorb smaller ones through gravitational interactions, contributing to their growth[4].
   • Galaxy Collisions: Collisions between galaxies can lead to mergers, triggering new bouts of star formation and altering the structure of the galaxies involved[4][5].

In summary, galaxy formation and evolution are driven by a combination of gravitational forces, dark matter, and mergers, leading to the diverse range of galaxy types observed in the universe today.

Key Points:

• Dark Matter: Essential for galaxy formation, providing gravitational scaffolding.
• Hierarchical Clustering: Small galaxies form first and merge to form larger ones.
• Mergers: Crucial for galaxy growth and evolution.
• Star Formation: Influenced by cold gas availability and triggered by mergers.
• Supermassive Black Holes: Play a significant role in galaxy evolution.

References:

• [1] https://www.space.com/how-galaxies-form
• [2] https://en.wikipedia.org/wiki/Galaxy_formation_and_evolution
• [3] https://www.atnf.csiro.au/outreach/education/senior/cosmicengine/galaxy_formation.html
• [4] https://science.nasa.gov/universe/galaxies/evolution/
• [5] https://science.nasa.gov/mission/webb/galaxies-over-time/

Sources:

• [1] http://www.space.com
• [2] en.wikipedia.org
• [3] http://www.atnf.csiro.au
• [4] science.nasa.gov
• [5] science.nasa.gov