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Our Universe StructureSmallest to largest:
PlanetsStars/Solar systemsGalaxiesGalaxy ClustersUniverse
Universe contains hundreds of billions of galaxies.
Galaxies contain hundreds of billions of stars.Imagine the possibility of finding life.
Life on other planets IS possible!If only one planet in each galaxy had life. . .
Now imagine the probability of finding it!1.0 X 1022!
Distance - factorsDistance indicators = objects
whose diameter or absolute magnitude is KNOWN
Look-back time = looking at galaxies millions of light-years away = looking at light that left galaxy millions of years ago, like looking back in time.
DistancesAstronomical Unit = distance between
Earth and Sun, 93 million mi. (solar system)
Recall: Light Year = distance light travels in one year, 9.46 X1015 m (near by stars)
Parsec = 3.08 X 1016 m = 3.26 light years (stars within our galaxy)
Megaparsec = 1 Mpc = 3.26 million light years (galaxy clusters & galaxies)
Types of Galaxies
SpiralEllipticalIrregular
Spiral Galaxies
Usually disk shaped with a greater concentration of stars in the center.
Arms sweep outward.20% of all galaxies - From nucleus10% of all galaxies - From a rigid bar
Tend to spin faster in the center.Contain both young and old stars
Has both gas and dust to make new stars!
Milky Way Galaxy
Spiral galaxy example100,000 L.Y. across10,000 L.Y. thick at the nucleusThree spiral arms (splintered)Our solar system is 2/3 way down one
arm (30,000 L.Y. away from nucleus)Spherical halo/bubble made of gas and
globular clusters.
Milky Way Edge View
Artist Milky Way Galaxy
Artist Milky Way Galaxy
Elliptical GalaxiesRange of shapes- round to oval
Depends on our frame of reference!Depends on eccentricity.
Most are small, but the largest galaxies known are elliptical200,000 L.Y. diameter
60% of all galaxiesNo arms or barsNo visible gas or dust-which means no
NEW stars are forming.Composed of old starsLack hot, bright starsStars concentrated near center.
Elliptical Galaxy NGC 4881
Irregular Galaxies
Make up 10% of known galaxiesComposed of young and old stars
Clouds of gas and dust w/o nucleus or arms Huge! Can see 2 with your eye alone
Large and Small Magellanic CloudsNamed after Magellan who discovered them
in 1520.150,000 L.Y. away, nearest neighbors
Large Magellanic Cloud
Small Magellanic Cloud
eaRTH SPACe scienceAll galaxy types represented.
Make your own at: http://mygalaxies.co.uk
Galaxy Clusters
Group of stars is a galaxyGalaxies are also grouped into clustersMay contain thousands of galaxiesOur cluster is called the Local Group
Has at least 28 galaxiesGalaxy clusters can be grouped into
superclustersBelieved to be the largest grouping in the
universe.
CollisionsMay dominate galaxy evolutionGalaxies collide, stars don’t
Galaxies are much closer together than stars
Causes rapid star formation and one may “steal” gas/dust from the other.Galactic cannibalismMilky way vs. Large & Small Magellanic
cloudsEvidence in distortions and computer
modelsLast a hundred million years
Galactic Cannabilism
Image of Lg. Magellenic cloud. Dots are stars stolen from Sm. Mag. Cloud. Proof = opposite rotation, odd orbits, and different composition of LMC. (rotation, orbit, & composition similar to SMC)
Cartwheel Galaxy
Hubble’s Law Edwin Hubble, 1929 Realized that dimmer galaxies are likely
farther away. The farther the galaxy, the greater the red
shift. Red shift = when a light source is moving away
from the observer, the light waves get “stretched” causing it to appear redder than it really is.
Hubble’s law - the farther the galaxy is from us, the faster it is moving away.
Vr=Hd, H = Hubble’s constant, value still being determined (70-100 km/sec/Mpc)
Red Shift
Top = Red shift: object moving away
Middle = No shift: object not moving toward or away
Bottom = Blue shift: object moving toward
Example: Sounds/Doppler Effect