Transcript Galaxies

SIZE OF MILKY WAY
Kapteyn
all visible stars – 30,000 parsecs
sun close to center
Shapley
globular clusters – 100,000 parsecs
sun 2/3 toward rim
Population I – blue, young, found in disk
particularly in arms, circular orbits, high
concentration (3%) heavy elements
Population II – red, old, found in bulge and halo,
elliptical orbits, low concentration of heavy
elements
Probably smooth transition between end
members (i.e. the sun).
? Population III ? – pure H and He
TWO MODELS OF STAR FORMATION
Density wave model
Self-propagating star formation model
Galaxy Shapes
spiral (S)
barred spiral (BS)
spiral with no arms (S0)
elliptical (E)
irregular (Irr)
Rotation of Galaxies
all stars follow velocity/gravity
relationships
all galaxies have too little visible
mass for rotation speeds
Any model for the formation and
evolution of galaxies must
account for collisions!
Other types of galaxies
Radio Galaxies
Seyfert Galaxies
Quasars
probably all black holes with accretion
disks
Stars are grouped in clusters and
galaxies
Galaxies are grouped in clusters.
Even clusters of galaxies are
clumped together.