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Chapter 16: Other Galaxies

Chapter 16: Other Galaxies. WHAT DO YOU THINK?. Do all galaxies have spiral arms? Are galaxies isolated objects? Are all other galaxies moving away from the Milky Way?. You will discover…. How galaxies are categorized by their shapes. That galaxies contain huge amounts of dark matter.

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Chapter 16: Other Galaxies

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  1. Chapter 16: Other Galaxies

  2. WHAT DO YOU THINK? • Do all galaxies have spiral arms? • Are galaxies isolated objects? • Are all other galaxies moving away from the Milky Way?

  3. You will discover… • How galaxies are categorized by their shapes. • That galaxies contain huge amounts of dark matter. • That galaxies are found in clusters. • How some galaxies merge while others devour their neighbors. • That the universe is expanding.

  4. Types of Galaxies • Spiral • Barred Spiral • Elliptical • Irregular

  5. Hubble’s Diagram of Galaxy Types

  6. 1. Spiral Galaxies Type Sa Type Sb Type Sc

  7. Andromeda (M31)

  8. Spiral Galaxies Seen Edge-on M104: Sa galaxy NGC 891: Sb galaxy NGC 4631: Sc galaxy

  9. Variety in Spiral Arms M33: A Spiral Galaxy with Flocculent Spiral Arms – created by explosions. M74: a Grand Design Spiral Galaxy – created by waves, like ripples in water.

  10. 2. Barred Spiral Galaxies M58: SBa galaxy M83: SBb galaxy NGC 1365: SBc galaxy

  11. 3. Elliptical Galaxies M105: E0 galaxy M49: E4 galaxy NGC 4526: E7 galaxy

  12. 4. Irregular Galaxies Large Magellanic Cloud, Irr 1 galaxy NGC 4485 (Irr 2) and NGC 4490 (Sc) galaxies

  13. Galaxies are Clumped in Space • Galaxies occur in groups called Clusters. The galaxies in a Cluster are bound by gravity to each other, and can collide. • Our Galaxy belongs to a Cluster called “The Local Group.” • Clusters of galaxies occur in bigger groups called Superclusters. Most Superclusters are not gravitationally bound units like Clusters are. • All the Clusters are moving away from each other as the Universe expands.

  14. A Cluster of Galaxies The Fornax Cluster of Galaxies

  15. The Local Group – Our Cluster Our Galaxy belongs to a poor, irregular (wimpy) cluster – consisting of about 40 galaxies (including M31 Andromeda) – called the Local Group.

  16. Colliding Galaxies • Galaxies that belong to the same Cluster can collide. • Sometimes these galaxies pass through each other, and sometimes they combine. • The individual stars in the colliding galaxies do not hit each other, but the huge clouds of gas and dust do collide.

  17. Colliding Galaxies Pairs of colliding galaxies often exhibit long “antennae” of stars ejected by the collision.

  18. Colliding Galaxies “Mano a Mano” NGC 2207 (right) and IC 2163 are orbiting and gravitationally distorting each other.

  19. Our Local Superclusterand Other Superclusters Our Local Group (cluster) is at the center of the diagram. Our Local Supercluster extends out to the Virgo Cluster.

  20. Beyond Superclusters –Filamentary Structure in the Universe 2-Micron All Sky Survey (Infrared) – 1.6 million galaxies shown.

  21. Beyond Superclusters –Filamentary Structure in the Universe Distribution map of 62,559 galaxies in two wedges extending out in opposite directions from the Earth (done with galaxy redshifts).

  22. The Universe is Expanding • The Redshift of Superclusters shows us that the Universe is expanding. This Redshift is called the “Cosmological Redshift,” because it is caused by the expansion of space. • The farther away a galaxy is from us, the faster it moves away from us: GALAXY SPEED = GALAXY DISTANCE x HUBBLE’S CONSTANT (H0). • This is called “Hubble’s Law,” after Edwin Hubble, who discovered it.

  23. Hubble’s Law The farther away a galaxy is from us, the faster it moves away from us: GALAXY SPEED = GALAXY DISTANCE x HUBBLE’S CONSTANT (H0).

  24. The Hubble Telescope looks back to when the Universe was very young.

  25. HST – Galaxies 12.5 Billion LY Away

  26. HST – Galaxies >13 Billion LY Away

  27. WHAT DID YOU THINK? • Do all galaxies have spiral arms? • No. Galaxies may be either spiral, barred spiral, elliptical, or irregular. Only spirals and barred spirals have arms. • Are galaxies isolated objects? • No. Galaxies are grouped in clusters, and clusters are grouped in superclusters. • Are all other galaxies moving away from the Milky Way? • All galaxies except those in our Local Group (cluster) are receding from us. Some local galaxies are actually moving toward us.

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