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Galaxies are not distributed randomly through space Concentrated in groups called Clusters Clusters range from about 10 13 M Sun to about 10 15 M Sun Range.

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Presentation on theme: "Galaxies are not distributed randomly through space Concentrated in groups called Clusters Clusters range from about 10 13 M Sun to about 10 15 M Sun Range."— Presentation transcript:

1 Galaxies are not distributed randomly through space Concentrated in groups called Clusters Clusters range from about M Sun to about M Sun Range in size from 2 Mpc to 10 Mpc across Clusters are categorized based on how many bright galaxies they have Bright is vague, but roughly brighter than 10% of the Milky Way The two types of clusters are rich and poor Rich – 50+ bright galaxies, (about M Sun ) Poor - <50 bright galaxies, (about M Sun or M Sun ) Sometimes these categories are called “groups” and “clusters” insteasd Group = Poor cluster Cluster = Rich cluster Clusters

2 It has about 50 total galaxies Three spiral galaxies – two of them large Milky Way Galaxy – a SBb or SBc Andromeda Galaxy (M31) – SBb Triangulum galaxy (M33) – Sc or Sd Several small satellites of these galaxies Several miscellaneous galaxies Total diameter about 2 Mpc The Local Group – our Cluster

3 Sagittarius Dwarf Elliptical Galaxy Larger Magellenic Cloud Smaller Magellenic Cloud Canis Major Dwarf Draco Dwarf Carina Dwarf Our Companions Sextans Dwarf Leo I Leo II Ursa Minor Dwarf Sculptor Dwarf

4 The Great Galaxy in Andromeda (M31) Large Spiral Galaxy - or probably barred spiral (SBb) About 50% brighter than our galaxy About the same mass as our galaxy 780 kpc away Two black holes in the center (!) Moving towards us at 300 km/s Will merge with us in 2.5 Gy?

5 M32 M110 NGC 147 NGC 185 Andromeda III Andromeda IV Andromeda V Pegasus Dwarf Cassieopeia Dwarf Companions of Andromeda

6 Triangulum galaxy (M33) Pisces Dwarf Phoenix Dwarf Leo A IC 10 IC 1613 Other Members of Local Group Tucana Dwarf Wolf-Lundmark- Melotte

7 The Virgo Cluster More than 1000 galaxies Dozens of bright galaxies Two giant ellipticals Many bright spirals 18  1 Mpc away A rich cluster Total mass about 1.2 × M Sun

8 The Coma Cluster galaxies visible Many bright galaxies Many giant ellipticals, especially in the center Bright spirals towards the edges About 100 Mpc away A very rich cluster Total mass about 3 × M Sun

9 Hydra Cluster Fornax Cluster Perseus Cluster HGC 87 Markarian’s Chain

10 Cluster Evolution Galaxy Clusters, like stellar clusters, will change over time Heaviest galaxies fall towards the center Tidal Friction will enhance this effect Galaxies will merge For rich clusters, over time: System will “virialize” to form a spherical distribution (more regular) Core will shrink, eventually galaxies overlap Giant ellipticals concentrated in the center Spirals more towards the edge. Collisions will knock gas out of the galaxies themselves Typically, twice as much gas between the galaxies as in the galaxies

11 Old Clusters Ancient Galaxy Cluster Old Galaxy Cluster

12 Where is the mass in a galaxy cluster? Most (all?) galaxies have much more mass than is in the stars and gas Dark Matter is 90% of galaxies How about clusters? Need to find mass of cluster Gravitational lensing! Observer Cluster Distant Source Gravity bends light You see two or more images of source Can estimate mass of cluster! There’s much more mass than is visible 5% is in stars and other visible matter 10% is in hot gas between the galaxies 85% is in dark matter

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16 Superclusters Clusters are themselves grouped into larger structures called Superclusters Size: Up to around 100 Mpc Our cluster is called the “Virgo Supercluster” Centered on the Virgo Cluster Superclusters are much more poorly defined than clusters They are probably not gravitationally bound! They haven’t had time to virialize They are always irregular, no particular shape to them Gravity hasn’t had time to reshape them Hence this represents primordial distribution of mass

17 Nearby Superclusters Between the superclusters are “voids” almost devoid of galaxies Little evidence of structure bigger than superclusters No “hyperclusters” Largest scale structure like soap bubbles Mostly empty space Superclusters are walls between the bubbles

18 On the largest scale:

19 Classification:Our Address Stellar systemSolar System Star Cluster(none) GalaxyMilky Way Galaxy ClusterThe Local Group SuperclusterVirgo SuperclusterUniverse Everyone should know where they live:


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