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18 Cards in this Set

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period luminosity relation
more massive stars pulsate more slowly than less massive stars

brighter stars=longer pds
based on gobular clusters..
galactic center is in direction of sagitarius
sun is not at center of galaxy, but does lie on disk
galactic components
1.disk=mostly stars, gas and dust. ongoing star formation
2.halo=spherical cloud of stars and gobular clusters. little gas and dust
3.nuclear bulge=dense, spherical cloud around center of galaxy. little gas and dust in outer region
population I stars
found in disk of galaxy
higher percentage of metals
circular orbits
relatively younger stars
population II stars
found in halo and bulge
lower percentage of metals
elliptical and tilted orbits
older stars
first stars
mostly hydrogen and helium
low mass stars still around
high mass stars evolved into supernova
halo and disk origin
1spherical cloud of dust gives birth to star/star clusters
2.rotating cloud begins to contract, leaving stars behind in halo w/ random motions
3.new generations of stars have flater orbitations and more ordered motions
4.disk of galaxy now very thin
density wave theory
orbiting gas clouds take spiral arms from behind.
compression of gas cloud triggers star formation
massive OB stars light up but die quickly
low mass stars live long but not luminous
age of galaxy
open clusters (in disk)=7 billion years old
globular clusters (in halo)=11 billion years old

disk younger than halo
sagitarius A
high lumionsity->lots of dust and crowded w/ stars
spiral arms of material flowing from disk to Sgt A*
Elliptical galaxy
egg-shaped
little gas or dust (no ongoing star formation)
reddish/yellowish color (lack of hot OB stars)
older stars
Spiral/Barred Spiral galaxy
"disk" galaxy
disk and spiral arms
lots of gas and dust (ongoing star formation)
bluish/whitish (hot luminous OB stars)
form new stars
Spiral galaxies classed based on...
1. amount of gas and dust
(Sa= least, Sc=most)
2. size of nuclear bulge
(Sa=largest, Sc=smallest)
3.tightness of spiral arms
(Sa=tightest, Sc=loosest)
Irregular galaxy
no clear pattern
gas, dust, stars
tully-fisher relation
rotation speed of galaxy directly related to total luminosity
greater mass=faster a galaxy rotates
greater mass=more light it gives off
local group
30-40 galaxies, mostly dwarf ellipticals
dominated by milky way and m31 (andromeda)
galaxy supercluster
dominated by Virgo cluster (2500 galaxies)
hubbles law
galaxies farther away-> moving away from us at faster and faster speeds