11GalaxiesGalaxiesPSC 203PSC 203 22OverviewOverviewIn this lecture:In this lecture:What types of galaxies are there?What types of galaxies are there?What are the features of each type?What are the features of each type? 33Galaxy typesGalaxy typesHow might we categorize galaxies?How might we categorize galaxies?(what properties could be used to classify (what properties could be used to classify galaxies)galaxies)SizeSizeShapeShapeBrightnessBrightness…… 44Hubble’s classificationHubble’s classificationHubble came up with a classification based Hubble came up with a classification based on…on…ShapeShapeWhat were his groupings?What were his groupings?Spiral / Barred SpiralSpiral / Barred SpiralEllipticalEllipticalIrregular / PeculiarIrregular / Peculiar 55Galaxy typesGalaxy typesVideoVideo, galaxy type overview, galaxy type overviewvideo 2, fainter galaxiesvideo 2, fainter galaxies 66Spiral GalaxiesSpiral GalaxiesDefinition …Definition …a galaxy with a disk in which its bright a galaxy with a disk in which its bright stars form a spiral pattern stars form a spiral pattern What galaxy have we already seen that is What galaxy have we already seen that is a spiral?a spiral?77Example ImageExample Image 88Example ImageExample Image 99Structuresame general structure as our galaxy:diskbulgehalospiral arms 1010Two types of spiralsTwo types of spiralsRegular spiralsRegular spiralsBarred SpiralsBarred Spirals 1111SizesSizesthey range somewhat in sizethey range somewhat in sizeMilky Way is Milky Way is 75,000 ly across75,000 ly acrosssmaller : smaller : 15,000 ly across15,000 ly acrosslarger : larger : 112,500 ly across112,500 ly across 1212Viewing AngleViewing Anglespiral galaxies look very different spiral galaxies look very different depending on the angle of the disk depending on the angle of the disk ““face on”: see top view, whole diskface on”: see top view, whole disk““edge on” see side view, edge of diskedge on” see side view, edge of disk1313““Face On” ExampleFace On” Example 1414““Edge On” ExampleEdge On” Example 1515““Tilted” ExampleTilted” Example 1616Elliptical GalaxiesElliptical GalaxiesDefinition …Definition …a galaxy in which the stars smoothly fill a galaxy in which the stars smoothly fill an ellipsoidal volume an ellipsoidal volume ellipse = flattened circleellipse = flattened circleellipsoidal volume = flattened sphere ellipsoidal volume = flattened sphere 1818SizeSizeranges greatlyranges greatlysmallest: smallest: 750 ly across750 ly acrosslargest: largest: 375,000 ly across375,000 ly across1919AppearanceAppearancespecks in halo are not stars but entire specks in halo are not stars but entire globular clustersglobular clusters 2020Example ImagesExample Images 2121Example ImagesExample Images 2222Example ImagesExample Images 2323Irregular GalaxiesIrregular GalaxiesDefinition … Definition … a galaxy lacking a symmetric structurea galaxy lacking a symmetric structure 2424StructureStructurecan take many formscan take many formskey is irregularity and asymmetry key is irregularity and asymmetry2525Example ImagesExample Images 2626Example ImagesExample Images 2727IrregularsIrregularsirregulars may irregulars may looklook like nebula like nebulabut they are really much, much largerbut they are really much, much larger 2828Peculiar galaxiesPeculiar galaxies 2929Interacting GalaxiesInteracting Galaxiessome irregulars form when galaxies some irregulars form when galaxies interactinteractgravity of one pulls on the othergravity of one pulls on the othermay even collidemay even collideend result is galaxy or galaxies with end result is galaxy or galaxies with distortionsdistortions 3030Example ImagesExample Images3131Example ImagesExample Images 3232CollisionsCollisionsWe will look at this next lecture ...We will look at this next lecture ... 3333In-Class Activity:In-Class Activity:describe the main features of each galaxy describe the main features of each galaxy