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 HubbleHubble UltradeepUltradeep FieldField Hubble's tuningHubble's fork Hubble's tuningHubble's fork Andromeda Milky Way LMC SMC Formation of Galaxies Hertzsprung-Russel Diagram Formation of Galaxies ⇒ ⇒ ⇒ More Massive Sequence: Main the Along
Lives Lives Burns Much Shorter Brighter Faster
DIM 0.001 Lum. (solar units) 1000 BRIGHT 10 1 6 10 10 HOT 7 7 30,000 yr yr 10 10 8 8 yr yr Surface temp. (K) Surface temp. 10 10 9 9 yr yr 10,000 10 10 10 10 10 10 yr yr 11 11 6,000 yr yr 3,000 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