Overview of Galaxy Formation
Galaxies form through the gravitational collapse of primordial gas clouds in the early universe, shortly after the Big Bang around 13.8 billion years ago. According to the hierarchical merging model in astrophysics, small density fluctuations in the cosmic microwave background grew into protogalaxies via dark matter halos, which provided the gravitational scaffolding. Over time, these merged to create larger structures like spirals and ellipticals.
Key Processes in Galaxy Evolution
Evolution involves star formation, where gas clouds collapse to ignite stars, feedback from supernovae and active galactic nuclei that regulate gas dynamics, and mergers that reshape morphology. Dark energy influences large-scale expansion, while dark matter dictates internal dynamics. Observations from telescopes like Hubble and JWST reveal redshifted light showing galaxies maturing from irregular to structured forms over billions of years.
Practical Example: The Milky Way's History
The Milky Way exemplifies this: it began as a small protogalaxy about 13 billion years ago, undergoing mergers like the recent Gaia-Enceladus event 10 billion years ago, which added stars and gas. Today, it's a barred spiral with ongoing star formation in spiral arms, illustrating how mergers drive evolution and bulge growth.
Significance in Astrophysics
Understanding galaxy formation and evolution tests cosmological models like Lambda-CDM, revealing the universe's composition (5% ordinary matter, 27% dark matter, 68% dark energy). It informs exoplanet searches, black hole studies, and the fate of cosmic structures, aiding predictions about the universe's expansion and eventual heat death.