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Our Universe Structure. Smallest to largest: Planets Stars /Solar systems GalaxiesGalaxy 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!
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Our Universe Structure • Smallest to largest: • PlanetsStars/Solar systemsGalaxiesGalaxyClustersUniverse • 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 - factors • Distance 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.
Distances • Astronomical 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 • Spiral • Elliptical • Irregular
Spiral Galaxies • Usually disk shaped with a greater concentration of stars in the center. • Arms sweep outward. • 20% of all galaxies - From nucleus • 10% 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 example • 100,000 L.Y. across • 10,000 L.Y. thick at the nucleus • Three 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.
Elliptical Galaxies • Range of shapes- round to oval • Depends on our frame of reference! • Depends on eccentricity. • Most are small, but the largest galaxies known are elliptical • 200,000 L.Y. diameter • 60% of all galaxies • No arms or bars • No visible gas or dust-which means no NEW stars are forming. • Composed of old stars • Lack hot, bright stars • Stars concentrated near center.
Irregular Galaxies • Make up 10% of known galaxies • Composed 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 Clouds • Named after Magellan who discovered them in 1520. • 150,000 L.Y. away, nearest neighbors
eaRTH SPACe science All galaxy types represented. Make your own at: http://mygalaxies.co.uk
Galaxy Clusters • Group of stars is a galaxy • Galaxies are also grouped into clusters • May contain thousands of galaxies • Our cluster is called the Local Group • Has at least 28 galaxies • Galaxy clusters can be grouped into superclusters • Believed to be the largest grouping in the universe.
Collisions • May dominate galaxy evolution • Galaxies 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 cannibalism • Milky way vs. Large & Small Magellanic clouds • Evidence in distortions and computer models • Last 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)
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