Presentation on theme: "Clusters and Superclusters"— Presentation transcript:
1 Clusters and Superclusters Galaxies are not distributed randomly through spaceConcentrated in groups called ClustersClusters range from about 1013 MSun to about 1015 MSunRange in size from 2 Mpc to 10 Mpc acrossClusters are categorized based on how many bright galaxies they haveBright is vague, but roughly brighter than 10% of the Milky WayThe two types of clusters are rich and poorRich – 50+ bright galaxies, (about 1013 MSun)Poor - <50 bright galaxies, (about 1014 MSun or 1015 MSun)Sometimes these categories are called “groups” and “clusters” insteasdGroup = Poor clusterCluster = Rich cluster
2 The Local Group – our Cluster It has about 50 total galaxiesThree spiral galaxies – two of them largeMilky Way Galaxy – a SBb or SBcAndromeda Galaxy (M31) – SBbTriangulum galaxy (M33) – Sc or SdSeveral small satellites of these galaxiesSeveral miscellaneous galaxiesTotal diameter about 2 Mpc
3 Our Companions Sagittarius Dwarf Elliptical Galaxy Leo I Canis Major DwarfLarger Magellenic CloudUrsa Minor DwarfLeo IISculptor DwarfSextans DwarfSmaller Magellenic CloudDraco DwarfCarina Dwarf
4 The Great Galaxy in Andromeda (M31) Large Spiral Galaxy - or probably barred spiral (SBb)About 50% brighter than our galaxyAbout the same mass as our galaxy780 kpc awayTwo black holes in the center (!)Moving towards us at 300 km/sWill merge with us in 2.5 Gy?
5 Companions of Andromeda NGC 147M110NGC 185Cassieopeia DwarfAndromeda VAndromeda IIIPegasus DwarfAndromeda IV
6 Other Members of Local Group Phoenix DwarfIC 1613Triangulum galaxy (M33)Wolf-Lundmark-MelotteTucana DwarfPisces DwarfIC 10Leo A
7 The Virgo Cluster More than 1000 galaxies Dozens of bright galaxies Two giant ellipticalsMany bright spirals18 1 Mpc awayA rich clusterTotal mass about 1.2 × 1015 MSun
8 The Coma Cluster 1000+ galaxies visible Many bright galaxies Many giant ellipticals, especially in the centerBright spirals towards the edgesAbout 100 Mpc awayA very rich clusterTotal mass about 3 × 1015 MSun
10 Cluster EvolutionGalaxy Clusters, like stellar clusters, will change over timeHeaviest galaxies fall towards the centerTidal Friction will enhance this effectGalaxies will mergeFor rich clusters, over time:System will “virialize” to form a spherical distribution (more regular)Core will shrink, eventually galaxies overlapGiant ellipticals concentrated in the centerSpirals more towards the edge.Collisions will knock gas out of the galaxies themselvesTypically, twice as much gas between the galaxies as in the galaxies
11 Ancient Galaxy Cluster Old ClustersOld Galaxy ClusterAncient Galaxy Cluster
12 Where is the mass in a galaxy cluster? Most (all?) galaxies have much more mass than is in the stars and gasDark Matter is 90% of galaxiesHow about clusters?Distant SourceNeed to find mass of clusterGravitational lensing!ObserverClusterThere’s much more mass than is visible5% is in stars and other visible matter10% is in hot gas between the galaxies85% is in dark matterGravity bends lightYou see two or more images of sourceCan estimate mass of cluster!
16 SuperclustersClusters are themselves grouped into larger structures called SuperclustersSize: Up to around 100 MpcOur cluster is called the “Virgo Supercluster”Centered on the Virgo ClusterSuperclusters are much more poorly defined than clustersThey are probably not gravitationally bound!They haven’t had time to virializeThey are always irregular, no particular shape to themGravity hasn’t had time to reshape themHence this represents primordial distribution of mass
17 Nearby SuperclustersBetween the superclusters are “voids” almost devoid of galaxiesLittle evidence of structure bigger than superclustersNo “hyperclusters”Largest scale structure like soap bubblesMostly empty spaceSuperclusters are walls between the bubbles
19 Everyone should know where they live: Classification: Our AddressStellar system Solar SystemStar Cluster (none)Galaxy Milky WayGalaxy Cluster The Local GroupSupercluster Virgo SuperclusterUniverse Universe