active galaxies and supermassive black holes chapter 17

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Active Galaxies and Supermassive Black Holes Chapter 17

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  • Active Galaxies and Supermassive Black HolesChapter 170

  • In the last few chapters, you have explored our own and other galaxies, and you are ready to stretch your scientific imagination and study some of the most powerful objects in nature. Supermassive black holes at the centers of galaxies are common but extreme. To study them, you will be combining many of the ideas you have discovered so far to answer four essential questions: What makes some galaxy cores active? How do supermassive black holes erupt? How did supermassive black holes form and evolve? How do supermassive black holes affect the evolution of their host galaxies and galaxy clusters?Guidepost0

  • The formation and evolution of supermassive black holes leads your astronomical curiosity outward into space and backward in time to the era of galaxy formation. In the next chapter, you will take the next step and try to understand the birth and evolution of the entire universe.Guidepost (continued)0

  • I. Active Galaxic NucleiA. Seyfert GalaxiesB. Double-Lobed Radio SourcesC. Quasars

    II. Supermassive Black HolesA. Disks and JetsB. The Search for a Unified ModelC. Triggering EruptionsD. Supermassive Black Holes Through TimeOutline0

  • Active GalaxiesGalaxies with extremely violent energy release in their nuclei (pl. of nucleus).Active Galactic Nuclei (= AGN)Up to many thousand times more luminous than the entire Milky Way; energy released within a region approx. the size of our solar system!0

  • The Spectra of GalaxiesTaking a spectrum of the light from a normal galaxy:The light from the galaxy should be mostly star light, and should thus contain many absorption lines from the individual stellar spectra.0

  • Seyfert GalaxiesUnusual spiral galaxies: Very bright cores Emission line spectra. Variability: ~ 50 % in a few monthsMost likely power source:Accretion onto a supermassive black hole (~107 108 Msun)0

  • Interacting GalaxiesSeyfert galaxy NGC 7674Active galaxies are often associated with interacting galaxies, possibly the result of recent galaxy mergers.Often: gas outflowing at high velocities, in opposite directions0

  • Cosmic Jets and Radio LobesMany active galaxies show powerful radio jetsRadio image of Cygnus AMaterial in the jets moves with almost the speed of light (Relativistic jets).Hot spots: Energy in the jets is released in interaction with surrounding material0

  • Radio GalaxiesCygnus A: A giant pair of radio jets. Jet visible in radio and X-rays; show bright spots in similar locationsCentaurus A (= Cen A = NGC 5128): Infrared image reveals warm gas near the nucleus.0Radio Image

  • Radio Galaxies (2)NGC 1265: Evidence for the galaxy moving through intergalactic materialRadio image of 3C 753C 75: Evidence for two nuclei recent galaxy merger0

  • Radio Galaxies (3)3C31: Member of a chain of galaxiesTwisted jets, probably because two galactic nuclei are orbiting each other.0

  • Formation of Radio JetsJets are powered by accretion of matter onto a supermassive black hole.Black HoleTwisted magnetic fields help to confine the material in the jet and to produce synchrotron radiation.Accretion Disk0

  • Active Galaxies in Galaxy ClustersThe powerful radio lobes of radio galaxies can push away intergalactic gas in galaxy clusters.0Even hundreds of millions of years after the Galaxys activity has calmed down, there are still ghost cavities in the X-ray emission from intergalactic gas.

  • QuasarsActive nuclei in elliptical galaxies with even more powerful central sources than Seyfert galaxiesAlso show very strong, broad emission lines in their spectraAlso show strong variability over time scales of a few months0

  • The Spectra of QuasarsThe Quasar 3C 273:Spectral lines show a large red shift ofz = Dl / l0 = 0.1580

  • Studying QuasarsThe study of high-redshift quasars allows astronomers to investigate questions of:1) Large scale structure of the universe2) Early history of the universe3) Galaxy evolution4) Dark matterObserving quasars at high redshifts: distances of several Gpc Look-back times of many billions of years The universe was only a few billion years old!0

  • Evidence for Black Holes in AGNsNGC 4261: Radio image reveals double-lobed jet structure; close-up view by Hubble Space Telescope reveals a bright central source embedded in a dust torus.0

  • Other Types of AGN and AGN UnificationRadio Galaxy:Powerful radio lobes at the end points of the jets, where power in the jets is dissipated.Cyg A (radio emission)Observing direction0

  • Other Types of AGN and AGN Unification (2)Emission from the jet pointing towards us is enhanced (Doppler boosting) compared to the jet moving in the other direction (counter jet).Quasar or BL Lac object (properties very similar to quasars, but no emission lines)Observing direction0

  • AGN Unification0Components of a Seyfert Galaxy or QuasarBroad Line RegionNarrow Line Region

  • Bursts of Activity of Supermassive Black HolesA star wandering too close to a supermassive black hole can be disrupted and trigger an X-ray outburst.0

  • Gallery of Quasar Host GalaxiesElliptical galaxies; often merging / interacting galaxies0

  • Quasars Through TimeQuasar activity in the Universe was most abundant at redshifts z ~ 2 3.0The highest-redshift quasars are seen at z > 6, but those are very rare.