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THE UNIVERSE AND ITS STARS

THE UNIVERSE AND ITS STARS. 13.5 Galaxies and Our Home: The Milky Way. Our Local Group. Milky Way galaxy has neighbours that are not moving away from each other like the rest of the universe is. Local Group includes 24 other galaxies and smaller systems, including our Milky Way.

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THE UNIVERSE AND ITS STARS

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  1. THE UNIVERSE AND ITS STARS 13.5 Galaxies and Our Home: The Milky Way

  2. Our Local Group • Milky Way galaxy has neighbours that are not moving away from each other like the rest of the universe is. • Local Group includes 24 other galaxies and smaller systems, including our Milky Way

  3. Our Local Group • Part of the Local Group is Orion’s sword. It is a birthing ground of stars and produces some very bright stars. • In another close-by galaxy, the Tarantula nebula is also a nursery to new stars. (image to right)

  4. Classifying Galaxies • Galaxies classified based on four basic shapes: 1) elliptical 2) spiral 3) barred-spiral 4) irregular

  5. Classifying Galaxies Elliptical Galaxies Roundest = E0 Most Elliptical = E7 -Very little interstellar matter -Thought to be quite old -Rarely form new stars Spiral Galaxies Our Milky Way is one of these Tightly wound spiral = Sa Loose spiral = Sc -Have interstellar matter -Full of new and young stars

  6. Classifying Galaxies Barred Spiral Galaxies Termed as SB galaxies. Tightly wound = SBa Loosely wound = SBc -Have well-defined bar of stars running through middle Irregular Galaxies -Have no definite outline or shape -Believed to be caused from the collision of two or more galaxies

  7. Classifying Galaxies One more classification was added: -Have central bulge and disk -Have NO spiral arms -Classified as S0 galaxies

  8. The Milky Way

  9. The Milky Way • Has about 200 billion stars (this is relatively low) • About 1.0 x 105 light years across • Bulge at centre of our universe is about 10 000 light years thick • Have approximately 4 – 6 arms in our galaxy • Sun is approximately 27 000 light years from centre • Takes 2.00 x 108 to 2.25 x 108 years to go around the galaxy once

  10. The Galaxy’s Centre • Thought to contain a black hole named Sagittarius A* (A* pronounced “A star”), which explains the X-rays and radio waves coming from centre of milky way • Sagittarius A* has mass of over 2 x 106 solar masses and a diameter that is 15 times the diameter of the Sun

  11. Quasars and Galaxy Clusters • Quasars are star-like objects that give off powerful radio waves • Are powered by supermassive black holes of about 1.0 x109 solar masses • Thoughttohavebeencreatedwiththecollision of twogalaxies • It can consumeothergalaxies

  12. Star Clusters • Groups of stars that stay together because of gravity and travel together through space. All stars in a group are same distance away from Earth and created from same material at same time • Globular Clusters: tight groups of thousands to millions of old stars • Mostare yellow or red, relatively cool, and small(under two solar masses) • Our Milky way has about 150 globular clusters scattered around centre • Open Clusters: only a few hundred stars, usually young stars in spiral arms (young meaning 10 to 30 million years old) • Much less densely packed that globular clusters, meaning much less tightly held together by gravity. Also means they’re more easily taken apart by neighbouring galaxies with strong gravity

  13. CYU p441 #10, 11, 14

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