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Galaxies - PowerPoint PPT Presentation

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Galaxies. Astronomy 315 Professor Lee Carkner Lecture 19. Upcoming Extra Credit Events. Thursday, April 27, 7pm, Olin Auditorium Andrew Knoll “Are We Alone in the Universe?” Thursday, May 4, 7pm, Olin Auditorium Kjell Lundquist

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Galaxies l.jpg

Astronomy 315

Professor Lee Carkner

Lecture 19

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Upcoming Extra Credit Events

  • Thursday, April 27, 7pm, Olin Auditorium

    • Andrew Knoll

    • “Are We Alone in the Universe?”

  • Thursday, May 4, 7pm, Olin Auditorium

    • Kjell Lundquist

    • “Stars Above, Stars Below and Stars Within: On Tycho Brahe, Uraniborg and a Garden Reconstruction”

  • Saturday, May 6, Planetarium

    • Planetarium Open House

  • Will receive 10 points extra credit on the observing project for each you go to (up to a maximum of 20 points)

  • See me there to sign in

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The Size of the Universe

  • Separate star systems like the Milky Way or just nebula in our galaxy?

  • In the 1920’s Edwin Hubble used the new 100 inch Mt. Wilson telescope to view Cepheids in “spiral nebula” and found they were too distant to be in our galaxy

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    Types of Galaxies

    • A visual inspection reveals 3 types:

    • Spiral

    • Elliptical

      • Composed of older stars

    • Irregular

      • Look like altered spirals

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    Spiral Galaxies

    • Spiral galaxies are similar to the Milky Way

    • Spiral arms contain gas and dust and young stars

    • We see a lot of spirals (~80% of bright galaxies)

      • Most smaller than the Milky Way

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    Classifying Spiral Galaxies

    • Spiral galaxies are classified based on two properties:

    • From this Hubble produced 3 categories:

    • Sa

    • Sb

    • Sc

      • Loosely wound arms, small bulge

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    Other Spirals

    • Many spiral galaxies show a bar of material across the nucleus (barred spiral)

    • Some galaxies have disks and bulges, but no spiral arms (called S0 or lenticular)

    • Why do spirals look the way they do?

      • Bars may form naturally, unless suppressed by a large dark matter halo

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    Elliptical Galaxies

    • Elliptical galaxies have almost no structure

    • Classified by how elongated they look from our point of view

    • Have almost no gas, dust or young stars

    • Have a wide range in size

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    Irregular Galaxies

    • Some galaxies have no discernable regular shape

    • Often show evidence of star formation

    • Distortion might be due to:

      • Galaxy collisions

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    Hubble’s Tuning Fork

    • Hubble categorized the galaxies and then placed them on a diagram

    • As you go from left to right in the diagram you roughly increase in gas, dust, number of young stars and star formation rates

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    Galactic Collisions

    • Galaxies should collide fairly often

    • What happens when they collide?

      • May trigger wave of star formation

      • One galaxy may merge with another (galactic cannibalism)

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    Evolution of Galaxies

    • It is not completely clear how galaxies evolve, but there is growing evidence for this basic picture

      • Burst uses up all gas and dust and star formation stops (Elliptical)

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    Next Time

    • Read Chapter 25.1-25.6