Structure/Formation of the Milky Way (a spiral galaxy) bulge: halo: ~10 billion years, ~13 billion years, AndromedaAndromeda GalaxyGalaxy formed early on almost as old as the Universe disk: 0...10 billion years stars still forming Past star formation Young and blue Old and Red Star formation going on A galaxy is an island of stars Elliptical galaxies are no longer forming stars, so they look red. GalaxyGalaxy EvolutionEvolution NatureNature oror Elliptical galaxies grow by NurtureNurture?? swallowing other galaxies. Abell 3827: clumps of stars were centers of consumed galaxies. It helps to be able to see galaxies when they are just born. More spiral galaxies Sombrero galaxy (infrared + optical) Look out into space = look back in time Face-on Giant molecularedge-on clouds Dusty lane where stars are being born Milky Way: currently forming stars in the disk at a rate of ~1 M /year sun mostly at spiral arms (the slow mode) star formation in the past much more intense (starbursts, the fast mode) new stars formed out of recycled materials; Galaxy-galaxyGalaxy-galaxy collisionscollisions induce starburst (the fast mode) induce starburstRadio (the fast mode) Visible M82 M81 UV and X-ray Our neighbor M82 has a star formation rate ~ 10 time higher (starburst). Lots of supernova and galactic superwind... Stars inside a galaxy Distance to nearest Galaxy 2,500,000light-year = =25 Diameter of Milky Way 100,000light-year Galaxies inside a group Local supercluster Local group 60 million Milky Way galaxy light-years virtually never Stars in open cluster 2.5 million 28,000 light-years light-years Universe common Earth Solar system (not to scale) Galaxies inside a cluster almost never Stars in globular cluster 0.04 light-seconds Collisions Collisions 8 light-minutes 5 light-seconds often Distance to nearest Star 3 light-year = =20million rare Diameter of Sun 5 light-second GalaxyGalaxy ClustersClusters LocalLocal GroupGroup The Andromeda galaxy Some galaxy-galaxy collision leads to merger and great starbursts. Central galaxies in galaxy clusters have undergone a lot of collisions and mergers. They are more massive and redder (oligarchs). The Milky way has cannibalized a number of smaller galaxies, and is eating more... RemainsRemains ofof ourour cannibalismcannibalism AlsoAlso forfor us,us, inin 2-32-3 billionbillion years?years? Andromeda-like Milky Way-like Or perhaps here You are here The sky will light up very brightly; the Sun may leave the galaxy, be incorporated into the mega-galaxy, or... Antannae UncertainUncertain FateFate StarburstsStarbursts inducedinduced byby mergersmergers Young and blue Or perhaps here You wind up here Something is astir in the centers of galaxies M87M87 Central black hole mass ~ a few billion solar masses Supermassive blackholes lurking in the center QuasiQuasi StellarStellar ObjectsObjects TheThe largerlarger thethe galaxy,galaxy, a blackhole outshining 100 billion stars? thethe biggerbigger thethe blackblack holehole Or are you joking? Black Hole in the Galactic Centre 6 M BH=3.6×10 M sun Did someone just drop a blackhole in our galactic center? SmallerSmaller fryfry Assignment 8 due next monday. AndromedaAndromeda GalaxyGalaxy ActiveActive GalacticGalactic NucleiNuclei Looks pretty steady... NGC 5548 NGC 3277 FormationFormation ofof GalaxiesGalaxies Hubble Ultradeep Field Ultradeep Hubble Hubble Ultradeep Field Ultradeep Hubble Hubble'sHubble's tuningtuning forkfork Along the 106 Main Sequence: Andromeda More Massive ⇒ Much Brighter BRIGHT 107 yr SMC ⇒ Burns Faster 1000 ⇒ Lives Shorter 108 yr 9 1 10 yr 1010 yr Lum. (solar units) Lum. (solar 1011 yr 0.001 LMC DIM Milky Way 30,000 10,000 6,000 3,000 Hertzsprung-Russel Diagram Hertzsprung-Russel Hertzsprung-Russel Diagram Hertzsprung-Russel HOT Surface temp. (K) COOL GalaxyGalaxy GroupsGroups MoreMore interactionsinteractions inin clustersclusters NGC 5350 group NGC 3166 group Leo group Abell 1185 Hubble Ultradeep Field Ultradeep Hubble Hubble Ultradeep Field Ultradeep Hubble 8 M84M84 M BH3×10 M sun NGCNGC 45284528 7 M BH=4×10 M sun CosmicCosmic MicrowaveMicrowave BackgroundBackground FormationFormation ofof StructureStructure Structure forms hierarchically: Differences in density: a few in 100,000! small things merge into big ones.