1	Chapter 14 Our Galaxy Chapter Outline The Milky Way Revealed Galactic Recycling: The Star-Gas-Star Cycle The History of the Milky Way The Mysterious Galactic Center
2	Our Galaxy
3	View Toward the Center of Our Galaxy
4	Galactic Orbits for Different Population Stars Halo stars possess elliptical orbits inclined at all angles to disk Bulge stars possess elliptical orbits but confined to bulge Disk stars possess nearly circular orbits while oscillating above and below central plane of the disk Sun Distance from center = 28,000 ly Orbital velocity = 220 km/s Orbital period = 230 million years
5	Stellar Census for Our Galaxy
6	Star-Gas-Star Cycle
7	Supercomputer Simulation of Supernova Superbubble
8	Atomic Hydrogen Gas
9	Giant Molecular Clouds
10	Star Formation Impact on Additional Star Formation
11	Varying Conditions in ISM
12	Matter Distribution in Disk of Our Galaxy
13	Galaxy Mass Distribution – Dark Matter
14	“Dark Matter” Observation: galactic rotation curve does not decline in Keplerian fashion far from center of Galaxy Actually grows larger toward edge of Galaxy Consequence: more mass controlling motion of stars than can be account for in terms of visible matter Stars, gas, and dust Conclusion: about 90% of mass of Galaxy is “dark matter” Matter that does not emitted radiation anywhere across the electromagnetic spectrum Common matter (baryonic matter) does not have such a property Biggest mystery in contemporary astronomy
15	Spiral Structure in Vicinity of Sun From Neutral Hydrogen Gas
16	Maintaining Spiral Structure Spiral-density wave forms spiral arm pattern Spiral arms are locus of star formation in our Galaxy
17	Observed Relationship for Stars, Gas, and Dust in Other Galaxies
18	Central Bulge of Our Galaxy Properties If unobscured, nucleus would have brightness and size of full moon It is probably dense concentration of old stars Brightest stars would be red giants of relatively low mass Radio emissions suggest that Sagittarius A is the Galactic center Few million solar masses of matter concentrated in size about 3 light years across, probably a supermassive black hole
19	Galactic Center at Various Wavelengths
20	Galactic Center in the Infrared
21	Motion of Six Stars Around Massive Center
22	Orbital Velocities
23	The Big Picture Absorption of radiation by the interstellar medium has prevented, until relatively recent times, development of a reasonably complete picture of our Galaxy’s structural and dynamic aspects. Stellar winds and supernovae explosions generate shock waves and plasma streams moving in the disk and out of the disk into the halo. These processes mix newly produced elements that collect into interstellar clouds for new star formation. Using orbital speeds of stars and gas clouds the mass distribution has been determined. Most of the gravitationally significant mass is in the halo not the disk, which is responsible for most of the visible light. This non-radiating matter is known as dark matter. Galaxies act as centers for recycling matter between old and new stars.