Galaxy formation is the process by which primordial gas and dark matter in the early universe coalesced to form the first galaxies. After the Big Bang, the universe was filled with nearly uniform hydrogen and helium gas. Small density fluctuations, amplified by dark matter gravity, caused gas to collapse into dark matter halos, forming the seeds of galaxies.
Key stages of galaxy formation include:
- Gas Accumulation: Baryonic gas fell into gravitational potential wells created by dark matter, cooling and condensing to form dense regions.
- Star Formation: Dense gas clouds collapsed under gravity to produce the first generations of stars, which began enriching the surrounding medium with heavier elements through supernovae.
- Galaxy Assembly: Smaller structures merged to form larger galaxies, contributing to the diversity of galaxy morphologies seen today.
- Feedback Processes: Stellar winds, supernovae, and early black hole activity regulated star formation and gas distribution, shaping galaxy evolution.
Observational evidence comes from:
- High-redshift galaxies, showing early stages of star formation and structure.
- Cosmic microwave background (CMB) fluctuations, which trace the initial density perturbations.
- Numerical simulations, which reproduce galaxy formation and growth consistent with observations.
In essence, galaxy formation is the birth of cosmic structures, turning diffuse gas and dark matter into the complex systems of stars, gas, and dark matter that populate the universe today.