PRESENTATION NAME

THE UNIVERSE AND ITS STARS13.5 Galaxies and Our Home: The Milky WayOur Local GroupMilky 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

Our Local GroupPart of the Local Group is Orions 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)

Classifying GalaxiesGalaxies classified based on four basic shapes: 1) elliptical 2) spiral3) barred-spiral4) irregularClassifying Galaxies

Elliptical GalaxiesRoundest = E0Most Elliptical = E7-Very little interstellar matter-Thought to be quite old-Rarely form new starsSpiral GalaxiesOur Milky Way is one of these Tightly wound spiral = SaLoose spiral = Sc-Have interstellar matter-Full of new and young starsClassifying Galaxies

Barred Spiral Galaxies Termed as SB galaxies. Tightly wound = SBaLoosely 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

Classifying GalaxiesOne more classification was added: -Have central bulge and disk-Have NO spiral arms-Classified as S0 galaxies

The Milky Way

The Milky WayHas about 200 billion stars (this is relatively low)About 1.0 x 105 light years acrossBulge at centre of our universe is about 10 000 light years thickHave approximately 4 6 arms in our galaxySun is approximately 27 000 light years from centre Takes 2.00 x 108 to 2.25 x 108 years to go around the galaxy onceThe Galaxys CentreThought 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 SunQuasars and Galaxy ClustersQuasars are star-like objects that give off powerful radio wavesAre powered by supermassive black holes of about 1.0 x 109 solar massesThought to have been created with the collision of two galaxies It can consume other galaxiesStar ClustersGroups 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 starsMost are 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 theyre more easily taken apart by neighbouring galaxies with strong gravity CYU p441 #10, 11, 14