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Clusters and Superclusters

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Presentation on theme: "Clusters and Superclusters"— Presentation transcript:

1 Clusters and Superclusters
Galaxies are not distributed randomly through space Concentrated in groups called Clusters Clusters range from about 1013 MSun to about 1015 MSun 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 1013 MSun) Poor - <50 bright galaxies, (about 1014 MSun or 1015 MSun) Sometimes these categories are called “groups” and “clusters” insteasd Group = Poor cluster Cluster = Rich cluster

2 The Local Group – our Cluster
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

3 Our Companions Sagittarius Dwarf Elliptical Galaxy Leo I
Canis Major Dwarf Larger Magellenic Cloud Ursa Minor Dwarf Leo II Sculptor Dwarf Sextans Dwarf Smaller Magellenic Cloud Draco Dwarf Carina 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 Companions of Andromeda
NGC 147 M110 NGC 185 Cassieopeia Dwarf Andromeda V Andromeda III Pegasus Dwarf Andromeda IV

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

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 × 1015 MSun

8 The Coma Cluster 1000+ 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 × 1015 MSun

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

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 Ancient Galaxy Cluster
Old Clusters Old Galaxy Cluster Ancient 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? Distant Source Need to find mass of cluster Gravitational lensing! Observer 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 Gravity bends light You see two or more images of source Can estimate mass of cluster!




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 Everyone should know where they live:
Classification: Our Address Stellar system Solar System Star Cluster (none) Galaxy Milky Way Galaxy Cluster The Local Group Supercluster Virgo Supercluster Universe Universe

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