Galaxies Lecture 01

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  • Galaxy Facts
    • Stars from the most massive component (95% of mass)
    • They sometimes have satellite galaxies
    • Dwarf galaxies are the most common
    • They come isolated or in groups
    • Groups contain tens of galaxies, clusters contain thousands.
  • Star Clusters vs. Galaxies
    • Clusters are a few pc across; galaxies are larger than 1 kpc.
    • Clusters have stars; galaxies have over .
    • Galaxies are always self-gravitating
    • Galaxies contain gas, dust, and cosmic rays
  • Dynamics of Stars
    • The stellar mass of galaxies completely determines the dynamics.
    • Calculating the collision time of stars:
    • Stars never collide (collision time greater than Hubble time).
  • Dynamics of Gas
    • Calculating collision time of gas:
    • Gas collides often on timescales of galactic dynamics
  • Energy Changes
    • Gas energy changes via heating and cooling
    • Stellar energy changes via changes in gravitational potential (ex. galaxy collisions, ejection of stars from a region)