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1Quiz Wednesday (galaxies)No Lab #2HW, To be posted2 pt extra Credit assignmentThe Tuning Fork• Edwin Hubble (busy guy!)organized these differentgalaxy types into a tuning forkshaped diagram• Ellipticals are labeled E0-E7– E0 is almost perfectly spherical,E7 is quite flattened• Spirals are labeled Sa – Sd– Sa galaxies have tightly woundarms and a large central bulge– Sd galaxies are loosely woundand have a small central bulge• Barred Spirals are labeled SBa– SBd– Same flow as the Spirals2Tully- Fisher RelationThe Tully-Fisher Method of measuring distances to spiralgalaxies is based on a relation between the speed of thegalaxy's rotation and its absolute luminosity. The existenceof the relation suggests that a) distant galaxies are more luminous, with greatervelocities. b) rotations of galaxies generate star formation andtherefore light. c) luminosity generates rotation. d) luminous galaxies have more stars, and therefore moremass.3Differences in Star andGas Content• Ellipticals:– Low in gas and dust, so containsmostly older Pop II stars– Contain very high temperature,very low density clouds of gasthat cannot condense into stars.• Spirals:– Lots of gas and dust, so haveactive regions of star formation– Have both Pop II and youngerPop I stars• Irregulars:– Many hot, young stars– Large amounts of interstellarmatter– Might be young galaxiesThe nuclei of most spiral galaxies appear redder than their spiralarms because of a) young blue stars in the arms, and old red ones in the nuclei b) emission nebulae and dust in the nuclei c) receding nuclei and advancing spiral arms (Doppler shifts) d) nuclear reactions4A look back in time• The Hubble Space Telescopewas pointed at a part of the skythat looked empty, taking a 100-hour exposure• Very distant galaxies weredetected, some closer than others• This technique allows us to seegalaxies at various stages offormation• These early galaxies tend to besmaller than the Milky Way, andto not fall into Hubble’sclassification schemeGalactic Collisions• Galaxies can collide, though not in the sense of a car accident!• The galaxies pass through one another, and their immensegravitational pull tears both galaxies apart!• Eventually, a new elliptical galaxy will form…5Galaxy collision and merger67Collision movies8Which of the following is least easily explainable as a result of interaction between galaxies? a) Some galaxies have long "tails" of stars. b) Rich, regular clusters are dominated by central giant ellipticals. c) Both spiral and elliptical galaxies are seen at very high redshift. d) Some galaxies seems to be undergoing bursts of star formation.9Rich and Poor Galaxy Clusters• Rich clusters:– Contain hundreds tothousands of member galaxies– Are roughly spherical, withthe largest galaxies near thecenter– Contain mostly elliptical andtype S0 galaxies– Lots of hot gas and dust• Poor clusters– Contain only tens of galaxies– Have a ragged, irregularappearance– More spiral and irregulargalaxiesSuperclusters• Clusters of clusters are calledsuperclusters– Contain a few to many dozenclusters of galaxies– Can be Mpc across!– The Local Group is part of theLocal Supercluster, shown at left.• The Local Supercluster is headingtoward a region of space knownas the Great Attractor, where thereare a large number of massivesuperclusters• There may be super-superclusters!10Large Scale Structure in the Universe• Using modern technology,astronomers have mapped thelocation of galaxies andclusters of galaxies in threedimensions• Redshift is used to determinedistance to these galaxies• Galaxies tend to form longchains or shells in space,surrounded by voidscontaining small or dimgalaxies• This is as far as we can


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UW-Madison AST 103 - The Tuning Fork

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