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Quasars and Other Active Galaxies

Quasars and Other Active Galaxies. Active galaxies are brighter, and emit more non-stellar radiation. In this chapter you will discover…. 5-10% of galaxies unusually bright, called active galaxies The most distant objects we can see: quasars

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Quasars and Other Active Galaxies

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  1. Quasars and Other Active Galaxies

  2. Active galaxies are brighter, and emit more non-stellar radiation

  3. In this chapter you will discover… • 5-10% of galaxies unusually bright, called active galaxies • The most distant objects we can see: quasars • Supermassive black holes are central engines for radio galaxies, quasars, Seyfert galaxies, & BL Lac objects • Distribution of Quasars is a key to the evolution of the Universe, and to the Big Bang Theory of its formation.

  4. Active Galaxy Types • Seyfert Galaxies: Spirals with very bright centers • Radio Galaxies: Ellipticals with huge emissions of radio energy in “lobes” • Quasars:Very tiny, distant objects • All have very bright, active galactic nucleii

  5. Active Galactic Nuclei • Seyfert Galaxies • spiral galaxies with incredibly bright, star-like center (nucleus) • they are very bright in the infrared • their spectra show strong emission lines Circinus

  6. Active Galactic Nuclei • Seyfert Galaxies The luminosity can vary by as much as the entire brightness of the Milky Way Galaxy!!

  7. Radio Galaxies

  8. Cygnus A Radio Image 635 Million light years away, and still one of the brightest radio sources in the entire sky!

  9. Active Galactic Nuclei • Radio Galaxies| • galaxies – usually giant ellipticals - which emit large amounts of radio waves • the radio emission come from lobes on either side of the galaxy; not the galaxy itself

  10. Radio Galaxy Lobes These lobes are swept back because the galaxy is moving through an intergalactic medium.

  11. X-ray/Radio Image of Centaurus A X-ray isblue; radio is red

  12. BL-Lac Objects Superbright Elliptical Galaxy

  13. Quasars A peculiar Star-like object, emitting lots of radio waves? But not with a stellar spectral fingerprint!

  14. Quasar Spectra • Star-like objects • spectra that look nothing like a star • Faint Hydrogen lines… • VERY red-shifted!

  15. Quasar Observations • emit light at all wavelengths • A hot dense source? • occasionally VERY strong radio sources • Associated with jets from galaxies in clusters

  16. Quasars Brightness varies in time!

  17. Quasars Brightness varies in time!

  18. Quasars • Show enormous redshifts VERY far away by Hubble’s Law • Show extreme variability  VERY small, in scales of a light-hours to light years ….and so…. Quasars must be some of the most powerful objects we know of in the universe!

  19. Quasar Distribution • Seen at greatest distances (earliest history of the universe!) • Not seen nearby…. But… • Quasar behavior in some nearer clusters

  20. Atheoretical model quasar • Must account for observations: • Small Size • Enormous energy output across spectrum • Source of Jets • Similar behavior in galaxies in clusters • Some radio synchrotron emission (indicating magnetic field) • Full spectrum emission

  21. A quasar model… • Supermassive Black Hole Engine • Formed as Galaxies are born… • Pulling in gas, dust, and stars into huge accretion disk

  22. A quasar model… • Generating jets of X-ray radiation for millions of years • “Quiet down” as fuel diminishes • “Re-ignited” during collisions & mergers of galaxies in clusters

  23. The energy is generated from matter falling onto a supermassive black hole… 1.2 x 109 M for NGC 4261 3 x 109 M for M87 …which is at the center (nucleus) of the galaxy. Quasar Energy Source?

  24. Quasar Energy Source? • Matter swirls through an accretion disk before crossing over the event horizon. • Gravitational energy lost like E = mc2 • 10 – 40% of this is radiated away • Process is very efficient

  25. A quasar model… • Works to explain quasars • Even Supermassive Black holes are TINY • Accretion Disk generates thermal spectrum, jets, magnetic fields • Highly variable as mass is pulled in and… • Works for active galaxies, too!

  26. Theory Observation

  27. Magnetic fields twisted Pull charged particles out of disk & accelerate like slingshot Particles bound to magnetic field; focused in a beam Quasar Jet Formation

  28. Model Quasar Accounts for Other Observations, too • Orientation determines what we see: • if beams points at us, see a quasar • if not, molecular clouds/dust of galaxy block view of nucleus • we see a radio galaxy or Seyfert • lobes are where jets impact intergalactic medium

  29. Hubble space telescope shows us that quasars do live in galaxies…they are Active Galactic Nuclei!

  30. If the theory is right --- all galaxies start with Black Holes!

  31. Evidence Quasars are distant? • Hubble’s Law • Association with Galaxies in clusters • Gravitational Lensing

  32. Essay Questions to Know! • What are active galaxies? How do active galaxies produce their energy? How do we know? • What are quasars, and where are they found? What do they tell us about the universe?

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