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Galactic Structures and Evolution Hannah Hasson Image credit: NASA, ESA

Galactic Structures and Evolution

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A brief overview of the base structures and evolution of galaxies

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Galactic Evolution and Phenomena

Galactic Structures and EvolutionHannah HassonImage credit: NASA, ESA1The Observable UniverseOver 100 billion galaxiesMany sizes, but few shapes dominateEach contains billions to trillions of starsRange from dwarf galaxies (100s of lyr) to giants (100,000s of lyr)

Image credit: NASA/WMAP Science TeamLarge Structures- The CMBGeneral Characteristics of GalaxiesMassive centerSupermassive black holesCan be active galactic nuclei (AGN)Spheroidal component Random trajectories, rotating around at different inclinationsDisk componentOnly in disk galaxies, rotating on plane in circlesSmaller galaxies can orbit larger ones (EX: Magellan Clouds)

Galaxy TypesSpiralEx: Milky Way!EllipticalEx: NGC 1132IrregularEx: Antennae Galaxies

Image credits: NASA/ESA

Spiral GalaxiesGenerally larger, whitish (younger stars)Center bulge w/ stars and gas rotating in disk Rotating disk stars bob up and down (disk thickness)Stars around outside of disk move at same speeds (due to dark matter)Halo and bulge have spheroidal, old populations Disk has distinctive spiral arms of star formationDense disk of gas = star formationSpecial Types of Spiral GalaxiesBarred SpiralElongated center bulgePossibly caused by tidal forces of gas clustersEx: Milky Way!LenticularDisk galaxy without spiral armsIntermediate galaxy class

Image credits: NASA/ESA

Elliptical GalaxiesMostly smaller, though can be almost any sizeElongated spheroidal shape Reddish (older, cooler stars)Little cool gas/dust, so little star formationLots of hot, ionized gasMost common galaxy type

Irregular GalaxiesBlobby shapes, whitish colorContain lots of gas and dust for star formationMore common at far distancesTherefore, common to younger universeBeginning/intermediate phase of galaxy formation?

Image credit: Kormendy/SDSSGalactic EvolutionIrregular galaxies formed from density distribution (CMB)Clustered into concentrated spheroidal/elliptical structuresSpheroidal clouds flatten, resulting in diskEliminate most of momentum in one dimension via collisions of gas & gravitySpiral arms density waves of gas flowing around diskBar spirals tidal forces from satellite clumps of gas that orbitHalo & bulge of galaxy already formed stars have less interaction (only gravity), so staying in random orbits

Collisions!Galaxies may also transcend phases via collisionOver billions of years, effectively combine into one galaxyStars almost never actually collideResults in elliptical galaxyWhen they collide, gas is flung outLess star formation!

Graphic credit: Mihos, MaxwellThe Future

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