types of galaxies spirals (77%) ellipticals (20%) irregulars (3%) national optical astronomy...
TRANSCRIPT
GALAXIES
Types of GalaxiesSpirals (77%) Ellipticals (20%) Irregulars (3%)
National Optical Astronomy Observatory images
Galaxy types: Spirals
a: NASA/Hubble Space Institute; b: Robert Gendler; c: Anglo-Australian Observatory
• spiral disk shape with arms
• central nuclear bulge
Spiral galaxies – side view
Spirals – top view
Spiral arms don’t wind up
Ripples in rotating water/gas/dust form spiral arms
Galaxy Types: Barred Spirals
• central bulge is elongated, like a bar
The Milky Way
Galaxy Types: Elliptical
(a) NASA; (b) RoyalObservatory, Edinburgh
• no spiral shape or arms
Elliptical Galaxy Variations
a: J. D. Wray, McDonald Observatory; b, c: 1999 Princeton University Press/Zsolt Frei and James E. Gunn
• neither spiral nor elliptical
• white & dusty
Galaxy Type: Irregular
Edwin Hubble(1889-1953)
Milton Humason
(1891-1972)
Hubble’s Classification System
Cosmic Distance Ladder
Hubble’s Law:
Velocity of Distant Galaxies Increases with Distance
Closer Galaxies move away from us
Farther Galaxies move away from us faster
Hubble’s Constant yields Age of Universe
Hubble’s Constant Tells Age:
H0 = Velocity/Distance = 1 / Time
Hubble’s Law:
Velocity = H0 x Distance
The Local Group
Neighborhood Superclusters
Large Scale Structure in the Universe
Colliding Galaxies
Gravitational Lenses and Dark Matter