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Galaxies are not randomly distributed

Large Scale Structure. Clusters and Groups. Stellar systems Stellar Clusters Galaxies Galaxy Groups and Clusters Galaxy Superclusters The Universe. Galaxies are not randomly distributed Concentrations categorized by number of bright galaxies (more than 10% of Milky Way galaxy luminosity)

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Galaxies are not randomly distributed

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  1. Large Scale Structure Clusters and Groups • Stellar systems • Stellar Clusters • Galaxies • Galaxy Groups and Clusters • Galaxy Superclusters • The Universe Galaxies are not randomly distributed • Concentrations categorized by number of bright galaxies (more than 10% of Milky Way galaxy luminosity) • Groups are smaller • Less than 50 bright galaxies • Typically about 1013MSun • Clusters are larger • 50 – 1000 bright galaxies • Typically 1014 – 1015MSun

  2. The Local Group – Our Group It has about 60 total galaxies • Two bright spirals • Milky Way Galaxy • Andromeda Galaxy (M31) • Several small satellitesof these galaxies • Mostly ellipticals and irregulars • Several miscellaneous galaxies • Triangulum (M 33) – a spiral • Total diameter about 6 Mly Q. 101: Why Called a Group?

  3. The Milky Way

  4. The Great Galaxy in Andromeda (M31) • Large Spiral Galaxy - or probably barred spiral (SBb) • About 50% brighter than our galaxy • About 50% more massive than our galaxy • 2.5 Mly away • Moving towardsMilky Way at 110 km/s • Will merge withus in 4 Gy?

  5. Our Companions Larger Magellenic Cloud Sculptor Dwarf Carina Dwarf Sextans Dwarf Ursa Minor Dwarf Draco Dwarf

  6. Our Companions Leo I Canis Major Dwarf Smaller Magellenic Cloud Sagittarius Dwarf Elliptical Leo II

  7. Companions of Andromeda Cassieopeia Dwarf M110 M32 NGC 147

  8. Companions of Andromeda Pegasus Dwarf NGC 185 Andromeda III Andromeda IV Andromeda V

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

  10. Some Nearby Groups of Galaxies Sculptor Group Maffei Group

  11. The Virgo Cluster • More than 1000 galaxies • Dozens of bright galaxies • Two giant ellipticals • Many bright spirals • 54 Mly away • Total mass about 1.2 × 1015MSun

  12. The Norma Cluster • Difficult to study because our galaxy in the way • About 220 Mly away • Total mass > 1015Msun • Near the center of our supercluster

  13. Other Clusters In Our Supercluster Abell 3574 Hydra Centaurus Fornax Eridanus

  14. The Coma Cluster • 1000+ galaxies visible • Many bright galaxies • Many giant ellipticals, especially in the center • Bright spirals towards the edges • About 300 Mly away • Total mass about 3 × 1015Msun • Center of Coma Supercluster

  15. Cluster and Group Evolution Galaxy Clusters and Groups change over time: • Heaviest galaxies fall towards the center • Tidal Friction will enhance this effect • Galaxies will merge For clusters, over time: • System will form a spherical distribution (more regular) • In the center, galaxies will coalesce • Giant ellipticals concentrated in the center • Spirals more towards the edge • Collisions will knock gas out of the galaxies themselves • Twice as much gas between the galaxies as in the galaxies Q. 102: Why Giant Ellipticals Mostly in Clusters?

  16. Old Clusters Old Galaxy Cluster Ancient Galaxy Cluster

  17. Where is the Mass in a Galaxy Cluster? • Galaxies have much more mass than is in the stars and gas • How about clusters? • Need to find mass of cluster • Gravitational lensing Distant Source Cluster Observer Much more mass than is visible • 5% is in stars • 10% is in hot gas • 85% is in dark matter • Gravity bends light • See multiple images • Can estimate mass of cluster

  18. Clusters as Gravitational Lenses

  19. Clusters as Gravitational Lenses

  20. Clusters as Gravitational Lenses

  21. Superclusters • Stellar systems • Stellar Clusters • Galaxies • Galaxy Groups and Clusters • Galaxy Superclusters • The Universe Groups/clusters are themselves grouped into larger structures called Superclusters • Size: Up to around 500 Mly • Our supercluster is called the “Laniakea Supercluster” • Book has this wrong – out of date! • Superclusters are much more poorly defined than clusters • At this scale, the universe hasn’t had time to reshape them • They are always irregular

  22. Laniakea Supercluster • Discovered 2014 • Study of “flow” of nearby clusters • Centered on Great Attractor, near Norma • 500 Mly across

  23. Structure Near Us • Laniakea Supercluster • Coma Supercluster • Perseus-Pisces Supercluster

  24. 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 wallsbetween the bubbles Q. 103: How Much of Space is Filled?

  25. Structure on the Largest Scale Sloan Digital Sky Survey

  26. Everyone Should Know Where They Live • Stellar systems • Stellar Clusters • Galaxies • Galaxy Groups and Clusters • Galaxy Superclusters • The Universe Classification:Our Address Stellar system Solar System Star Cluster (none) Galaxy Milky Way Galaxy Group/Cluster The Local Group Supercluster Laniakea Universe Universe

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