1 Lecture 36 Quasars and Active Galaxies [not on exam] January 16a, 2014 2 Active Galaxies • Emit much more energy than average galaxies (100,000 times in some cases) • More seen at larger distances (past) • Galaxies radiate light at different wavelengths than normal galaxies – normal -- most light in visible wavelengths – active galaxy -- most light in radio and infrared 3 Quasars • 1960 – Allan Sandage – Observed strong radio source 3C 48. – Found star-like object at source with unidentified emission lines. • Later others were found. – 3C 273: Emission lines were extremely red-shifted hydrogen lines 3C 273 – Source was 600 Mpc away (2 billion light years)! • Quasi-stellar objects = quasars 4 Quasars • Quasars are very bright sources and are at distances very luminous – Can be 1000’s of times more luminous than the Milky Way. – Do not emit much blackbody radiation. • Now know of ~10,000 quasars. – Most have distances > 1000 Mpc (3 billion light years) – No nearby quasars = no recent quasars 5 Quasars are in Distant Galaxies • Host galaxies often appear distorted and have companion galaxies. 6 Active Galaxy – a galaxy that is much more luminous than ordinary galaxies. Two kinds – Seyfert galaxies and radio galaxies Peculiar Galaxy – any galaxy that appears to be blowing apart 7 Seyfert Galaxies • Spiral galaxy with very bright nucleus • Less luminous than quasars • Most are seen at large distances • Most emission comes from small region in the active galactic nucleus (bright core) – Center ~10,000 times brighter than core of MW • Luminosity fluctuates with time • Most energy emitted in radio and IR not stars • Broad, strong emission lines not stars 8 Seyfert Galaxy 9 Seyfert Galaxy 10 Radio Galaxies • Core-Halo galaxies – Small central core – Halo of radio emission around it Figure 24.24, Chaisson and McMillan, 6th ed. Astronomy Today, © 2008 Pearson Prentice Hall 11 • Lobe Radio Galaxies – Small nucleus – Large radio lobes extend from galaxy – Lobes possibly material ejected from central galaxy Galaxy Cygnus A appears to really be two galaxies colliding. It displays huge radio-emitting lobes on either side of the optical image. Figure 24.23, Chaisson and McMillan, 6th ed. Astronomy Today, © 2008 Pearson Prentice Hall 12 • The two types radio galaxies are likely the same object, just seen from different angles Figure 24.25, Chaisson and McMillan, 6th ed. Astronomy Today, © 2008 Pearson Prentice Hall 13 Active Galaxy Engine • Possible Theory: Supermassive Black Holes – Supermassive (>1,000,000 suns) black hole is in core of galaxy – Infalling gas and stars form accretion disk – Material heated by collisions in disk and interacts with magnetic field – Emits large amounts of radiation 14 Figure 24.31, Chaisson and McMillan, 6th ed. Astronomy Today, © 2008 Pearson Prentice Hall 15 • Disks have been observed near centers of some of these galaxies Figure 24.32, Chaisson and McMillan, 6th ed. Astronomy Today, © 2008 Pearson Prentice Hall .