The Milky WayThe Milky Way

Structure of the

Milky Way

The Milky WayThe Milky Way

Components of the Milky Components of the Milky WayWay

• DiskPopulation I starsOpen clustersHII regions

• BulgePopulation II stars

• HaloGlobular clusters

Omega CentauriOmega Centauri

Stellar PopulationsStellar Populations

M100

Finding Our PlaceFinding Our Place

Sun

Early viewSun at center

Harlow Shapley

Globular Clusters evenly distributed

Globular Clusters unevenly distributed

Mapping the GalaxyMapping the Galaxy

• Visible LightStrong interstellar absorptionWe can see only 4000 - 5000 pcs

• Radio LightCan observe entire galaxy

21-cm Radiation21-cm Radiation

Proton

Electron

Mapping the GalaxyMapping the Galaxy

• H clouds in different spiral arms will have different Doppler Shifts

Sun

Wavelength

21-cm Data21-cm Data

Galactic Rotation CurveGalactic Rotation Curve

Observed Rotation CurveObserved Rotation Curve

Keplerian Orbits

Dark Matter HaloDark Matter Halo

Dark MatterDark Matter

• There must be significant amount of mass in the Galaxy in an underluminous form (perhaps as much as 90% of total)Compact Objects - White Dwarf, Neutron

Stars, Black HolesMACHO’s - MAssive Compact Halo Objects

Planets, Brown DwarfsWIMP’s

Weakly Interacting Massive Particles