The Milky Way Galaxy This is a picture of the Sombrero Galaxy NOT The Milky Way

Discovery of The Milky Way What makes it so difficult to find our place in the galaxy?

Use of Variable Stars Giant stars whose brightness variesVariable Stars: Giant stars whose brightness varies –2 types 1.RR Lyrae 2.Cepheid variables Help to find distance to galactic centerHelp to find distance to galactic center Easy to find their luminosity, so you know luminosity, can find the distanceEasy to find their luminosity, so you know luminosity, can find the distance

Milky Way’s Shape Barred Spiral Galaxy It has a central bulge Spiraling arms outward from the center Looks much like a pinwheel, windmill, or a snail shell Use Hydrogen emission to study spiral arms NAME _____________________________

Milky Way as seen from Earth

Milky way Dimen Milky way Dimensions

Milky Way’s Mass (Star Count) Contains about 100 billion stars in the diskContains about 100 billion stars in the disk Believed that 90% of its mass is in the Halo, but is invisibleBelieved that 90% of its mass is in the Halo, but is invisible Possible super massive black hole in the centerPossible super massive black hole in the center Evidence for black holeEvidence for black hole –Strong x-rays given off –2.6 mil. times mass of sun crammed in the size of solar system

What’s the Milky Way Made Of? Stars and high concentrations of dust & gasStars and high concentrations of dust & gas Globular clusters: oldest star clusters in the galaxy found in the halo (12-14 bil. yrs old)Globular clusters: oldest star clusters in the galaxy found in the halo (12-14 bil. yrs old) Population I Stars in the diskPopulation I Stars in the disk –Younger stars –High amounts of heavy elements (O, C, N, etc.) Population II Stars in bulge/haloPopulation II Stars in bulge/halo –Older stars –Low amounts of heavy elements (O, C, N, etc.)

Population I & II Stars