INTRODUCTION TO ASTRONOMY
INTRODUCTION TO ASTRONOMY AST 301
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This 3 page Class Notes was uploaded by Keegan Goyette on Sunday September 6, 2015. The Class Notes belongs to AST 301 at University of Texas at Austin taught by John Kormendy in Fall. Since its upload, it has received 10 views. For similar materials see /class/181758/ast-301-university-of-texas-at-austin in Astronomy at University of Texas at Austin.
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Date Created: 09/06/15
Our Galaxy The Milky Way gtour galaxyrotating disk of stars gtspira galaxy gtbulge center of galaxy gtspira arms bue arms blue means young stars gtsbc spiral bar gtdiameter of disk 100 k light years The Sun gtfar away from center 30 k light years away from center of galaxy Kants Hypothesis gtthe galaxy is flat spinning disk of star gtother nebulae similar quotisland universes Shapley s discovery gtfound center of galaxy saw stars surrounding something so by gravity since most mass was concentrated in one area that s where center of galaxy was gtwe don t see the center of galaxy because theres lots MM radiation and light gtcenter very bright stars with longer periods will be brighter Star Types gtPopulation 1 young made in the arms of spiral galaxiesalways in the disk circe orbits near center gtPopulation 2 old in the bulge of galaxy random orbits not in same plane GalaxiesDark Matter Elliptical Galaxies gt3d like eggs gtcontain billions of stars reddish because old stars motion random gtfeatureless gtno arms gtno gas so no star formation gtmade up of old stars no young stars Spiral Galaxies gtbuge center of galaxy gtspiral arms bue arms blue means young stars gtSpiral barred So spiral flat disk featureless Sa bigger bulge arms tight around center Sb smaller bulge arms lose Sc smaller bulge arms looser than Sb Irregular Galaxies gtsome features but you can t characterize them gtformation collisions between galaxies things go everywhere temporarily become irregulars result is elliptical galaxy Cosmic Humility gtwe live in no special place gta lot we don t know gtwe don t even have the same matter you find in galaxies gtno center to universe Dark Matter gtvisibe mattereverything we ve talked about universe is 4 mass gtdark matterunknown composition that makes up 96 of universe everything else Evidence of Dark Matter gtdark matter in clusters of galaxies to keep galaxies from flying out of cluster there has to be a lot of mass gtdark matter halo of galaxies individua galaxies rotate faster even away from center when usually they should be slowingdown because of their large radii this mean there is dark matter present gtdark matter x ray gas contain halos of hot xray emitting gas gas should fly away so more mass has to present to hold gas so dark matter must be there gtstars in dwarf galaxies move so fast that they shouldmove away but instead don t gtdark matter light bending gravitational pull bends light from very distant objects distorted images of background galaxies imply clusters contain much for mass than we see Galaxies formations expansion of universe redshit meausure distance to galaxies Calibrating distance scale gtin order to measure distances to far away objects we need to calibrate or measurement methods over a variety of distances gtspectroscopic parallax We can find distances to more distant stars by measuring spectral type gtcepheid variable stars that satisfies period luminosity relation Al cepheids of same period have same absolute luminosity Used to measure other distances of galaxies by observing how long it takes for them to vary in brightness Hubbles law gtmeasured distances to galaxies gthubbleconstantuniverse is expanding at a faster and faster rate eq vHd recession velocity and distance are proportional Velocity measured via redshift constant 72 kmsecmpc Galaxy Formation gtgravitational clustering at start of universe there was nothing density of matter was almost the same everywhere some areas with larger than avg densities pulled gravitationally on their surroundings this caused for matter to come caused area to keep becoming dense and unstable then finally collapse and make galaxies and cluster of galaxies hierarchal clustering galaxies keep forming bigger galaxies gta clusters density contrast is diluted by projection clusters don t stand out well in projection Colliding and merging gttida interactions bridges and tails due to tidal forces acting on galaxy galaxy develops tidal tail that may stretch out far tidal spirals perturbed disk galaxies often develop striking spiral structure gtmergers slow collisions are more damaging than fast ones because gravity has more time to distort galaxy during collision tidal forces cause galaxies to collide galaxies collide and because the distortion requires the energy of the relative motion energy galaxies move slower and stay closer together after a lot of collisons galaxy lost so much orbital energy that theyjust form one giant galaxy during this time gravity sends stars hurdling into random disks result is elliptical Differences between bulges ellipticals and disks gteliptical formed their stars before or during the collapse of the meger gtdisks formed their stars after the collapse that made the galaxy material that made disk had to be gas Our Local Group gt24 galaxies in our local group gtGalaxies in our local group are getting closer to each other gtMeasured in redshift but since galaxies are coming towards us we call it quotblueshiftquot