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Quasars and Other Active Galaxies

Quasars and Other Active Galaxies. In this chapter you will discover…. 5-10% of galaxies unusually bright, called active galaxies The most distant objects we can see: quasars Evidence for unusual spectra and small volumes Models of quasars Tests of those models closer to the Milky Way

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Quasars and Other Active Galaxies

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  1. Quasars and Other Active Galaxies

  2. In this chapter you will discover… • 5-10% of galaxies unusually bright, called active galaxies • The most distant objects we can see: quasars • Evidence for unusual spectra and small volumes • Models of quasars • Tests of those models closer to the Milky Way • Extremely powerful BL Lac objects • Supermassive black holes are central engines for radio galaxies, quasars, Seyfert galaxies, & BL Lac objects

  3. 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?

  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 • spiral galaxies with incredibly bright, star-like center (nucleus) • very bright in the infrared • their spectra show strong emission lines Circinus 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 (~10% of time) VERY strong radio sources • Associated with jets from galaxies in clusters

  16. 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!

  17. Quasar Distribution • Seen at greatest distances (earliest history of the universe!) • Quasar behavior in some nearer clusters

  18. 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

  19. A quasar model… • Supermassive Black Hole formed as Galaxies are born… • Pulling in gas, dust, and stars into accretion disk • Generating jets of X-ray radiation for millions of years • “Re-ignited” during collisions/mergers of galaxies

  20. 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?

  21. 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

  22. 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!

  23. Theory Observation

  24. Formation of the Jets magnetic fields in accretion disks are twisted they pull charged particles out of the disk and accelerate them like a slingshot particles bound to magnetic field; focused in a beam Quasar Jets

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

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

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

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

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