Northeastern Illinois University Our Galaxy The Milky Way Greg Anderson Department of Physics & Astronomy Northeastern Illinois University Spring 2018 c 2012-2018G. Anderson Universe: Past, Present & Future – slide 1 / 91 Northeastern Illinois Overview University The Milky Way ISM Nebula Galactic Recycling Evolution The Galactic Center Review c 2012-2018G. Anderson Universe: Past, Present & Future – slide 2 / 91 M31: The Andromeda Galaxy NGC 4565: The Needle Galaxy SA(s)b Northeastern Illinois University Andromeda NGC 4565 The Milky Way The Night Sky Etymology Moments in History Q: Galactic Fog Milky Way M13 Q: Disk The Milky Way Thickness Q: Disk Diameter Q: Galactic Halo Milky Way Orbits Galactic Merry-Go-Round Fig 14.02 Q: Bobbing Stars Galactic Mass from Orbital Velocity Q: Orbital Speed Q: Sun’s Orbit Milky Way Milky Way Spiral Arms Spiral Arm – Theory c 2012-2018G. Anderson Universe: Past, Present & Future slide 5 / 91 c Matipon Tangmatitham Northeastern Illinois Etymology University • The English word galaxy is derived from the greek γαλαξιας (galaxias) meaning milky. • The English Milky Way is derived from from Latin Via Lactea from the Greek γαλαξιας κυκλoς´ aka Milky Circle. c 2012-2018G. Anderson Universe: Past, Present & Future – slide 7 / 91 Northeastern Illinois Moments in History University • Galileo Galilei first resolved the band of light known as the Milky Way into individual stars with his telescope in 1610, demonstrating the hypothesis of Anaxagoras and Democritus (5th century BCE). • Galactocentrism: 1785 William Herschel: Sun at center of flattened disk. (His view through the disk was obstructed by the “fog” of interstellar medium) • 1918 Harlow Shapley: globular clusters centered on a point 50,000 ly 27,000 ly from us. • Heber Curtis (1917) & Edwin Hubble (1920) demonstrated that spiral “nebulae” were actually distant galaxies beyond the Milky Way. c 2012-2018G. Anderson Universe: Past, Present & Future – slide 8 / 91 Northeastern Illinois Q: Galactic Fog University How does the interstellar medium affect our view of most of the galaxy? A) It prevents us from seeing most of the galactic disk with visible and ultraviolet light. B) It absorbs all wavelengths of light. C) It produces so much visible light that it blocks our view of anything beyond it. D) It has no effect on visible-light observations, but prevents us from studying the galactic center with radio waves or X-rays. c 2012-2018G. Anderson Universe: Past, Present & Future – slide 9 / 91 Northeastern Illinois Q: Galactic Fog University How does the interstellar medium affect our view of most of the galaxy? A) It prevents us from seeing most of the galactic disk with visible and ultraviolet light. B) It absorbs all wavelengths of light. C) It produces so much visible light that it blocks our view of anything beyond it. D) It has no effect on visible-light observations, but prevents us from studying the galactic center with radio waves or X-rays. c 2012-2018G. Anderson Universe: Past, Present & Future – slide 9 / 91 Theb Milky Way b b b b b b b b b b b b b b b b b b b b b b b b b b b b Halo b b b b b b b b b ∼ 150 Globular Clusters b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b Bulgeb b b b b b b Sgrb A* b b b b b b b b b b b b b b b b b Sun 27,000 ly from galacticb center Disk b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b 12 200 billion stars, 100, 000 ly diameter, 1, 000 ly thick, M & 10 M⊙ Globular Cluster: M13 (NGC 6205) Northeastern Illinois Q: Disk Thickness University What is the thickness of the Milky Way’s disk? A) 100 light years B) 1,000 light years C) 10,000 light years D) 100,000 light years E) 1,000,000 light years c 2012-2018G. Anderson Universe: Past, Present & Future – slide 12 / 91 Northeastern Illinois Q: Disk Thickness University What is the thickness of the Milky Way’s disk? A) 100 light years B) 1,000 light years C) 10,000 light years D) 100,000 light years E) 1,000,000 light years c 2012-2018G. Anderson Universe: Past, Present & Future – slide 12 / 91 Northeastern Illinois Q: Disk Diameter University What is the diameter of the Milky Way’s disk? A) 100 light years B) 1,000 light years C) 10,000 light years D) 100,000 light years E) 1,000,000 light years c 2012-2018G. Anderson Universe: Past, Present & Future – slide 13 / 91 Northeastern Illinois Q: Disk Diameter University What is the diameter of the Milky Way’s disk? A) 100 light years B) 1,000 light years C) 10,000 light years D) 100,000 light years E) 1,000,000 light years c 2012-2018G. Anderson Universe: Past, Present & Future – slide 13 / 91 Northeastern Illinois Q: Galactic Halo University What kinds of objects lie in the halo of our galaxy? A) open clusters B) hot, young blue giants C) globular clusters D) gas and dust E) all of the above c 2012-2018G. Anderson Universe: Past, Present & Future – slide 14 / 91 Northeastern Illinois Q: Galactic Halo University What kinds of objects lie in the halo of our galaxy? A) open clusters B) hot, young blue giants C) globular clusters D) gas and dust E) all of the above c 2012-2018G. Anderson Universe: Past, Present & Future – slide 14 / 91 Dark Matter Halo b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b bbb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b bb b b b b b b b b b b b b b b b b b b b Northeastern Illinois Orbits University b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b bb bbb b b b b b b b b b b bb b b b b b b b b b b bb b b b b b b b b bb b b b bb b b b b b bb b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b bb bb b b b b b b b b b b b b b b b b bb b b b b b b b b b b bb b b b b b b b b b b b b bb b b b b bb b b b b b b b b b b b b b bb bb b bb bb b b b b b b b b b b b b b b b b b bb b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b bb b b b bb b b b b b b b b b b b bb b b b b b b bb bb b b bb b b b b b b b b bb b b b b b b b b b bb b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b bb b b b b b b b b b b b b b b b bb b bbbbb bb b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b bb b b b b