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The Milky Way Galaxy Astronomy 315 Professor Lee Carkner Lecture 16.

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Presentation on theme: "The Milky Way Galaxy Astronomy 315 Professor Lee Carkner Lecture 16."— Presentation transcript:

1 The Milky Way Galaxy Astronomy 315 Professor Lee Carkner Lecture 16

2 Via Lactia   The band forms a complete ring  We seem to be in the center of a disk of stars    Clouds of gas and dust block our view so it is hard to see beyond our local region

3 Our View of the Milky Way

4 The Milky Way from Outside

5 Discovering The Galaxy  In the early part of the century Harlow Shapley found the distance to globular clusters using Cepheid variables  Globular clusters  Unlike stars in the disk, we can see distant globulars  Cepheid variables  If we can find luminosity and flux we can get distance (F = L/4  d 2 )

6 The Center  Shapley found the distance to the globulars and plotted their positions  He found:    We are not at the center of the galaxy and the disk extends out much further than we can easily see

7 Changing Views of the Galaxy

8 How Do We Learn About The Milky Way?  Optical observations   Radio observations   Infrared observations   Observing other galaxies  Since we are in the middle of the Milky Way we can’t get an overview of it

9 Structure of the Milky Way  Disk   Nucleus   Halo  Spherical distribution of old stars and globular clusters around disk and bulge

10 Edge-on and Face-on

11 The Disk  The disk is very thin   Younger stars and star forming regions near the center, older stars above and below   Disk exhibits differential rotation (inner parts rotating faster than outer)

12 Differential Galactic Rotation

13 Spiral Structure  We know that other galaxies have spiral structure, but it is harder to see the Milky Way’s  We find spiral arms by tracing:    They are not uniformly distributed but are found in a loose spiral structure  How do spiral arms form?

14 Local Spiral Arms

15 Density Waves  Spiral arms are like traffic jams   This can trigger star formation in the arms   The clouds eventually move out the other side   The spiral arm material changes, only the pattern stays the same

16 Density Wave

17 At the Core   The nucleus is the hardest part of the galaxy to observe due to all the gas and dust   One, Sagittarius A* (Sgr A*), may be the center of the galactic core  What is it?

18 Properties of the Core  Stars near the core are very close together and moving very fast   Sgr A* is emitting enormous amounts of energy   A black hole

19 Massive Black Holes  Sgr A* does not move and may have jets and and accretion disk   Mass of ~1 million solar masses?    Our own is very hard to observe

20 The Halo  The halo are stars orbiting in a large sphere around the galaxy  The halo is composed of old stars   Halo stars -- Population II -- metal poor  Disk stars -- Population I -- metal rich   Halo stars formed formed early from relatively unprocessed material

21 Globular Clusters   Size:  Shape:  Contents:  Globulars are in elliptical orbits around the galactic center  Unlike open clusters in the disk, globular clusters are very tightly gravitationally bound

22 History of the Milky Way  How did the galaxy form?    Basic theory has Milky way forming from large spinning cloud of gas   Halo formed first, and so is older and more metal poor  Disk is denser and so keeps forming stars and building up metals

23 Next Time  Quiz #2  Covers lectures 10-15  same format as quiz #1  multiple choice and short answer/problems  Read 19.5-19.6 and do homework for Friday  Observing Thursday (April 20), 8:30-9:30 pm  If you have not yet observed

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