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ACTIVE GALACTIC NUCLEI

ACTIVE GALACTIC NUCLEI. Pinpoint nuclei emitting intense light can be 100 x entire galaxy ! Incredibly compact: < size of Solar System “Nonstellar” (“nonthermal”) spectrum of radiation Spectral lines smeared out in wavelength interpret by Doppler shift atoms move at ~10% c

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ACTIVE GALACTIC NUCLEI

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  1. ACTIVE GALACTIC NUCLEI • Pinpoint nuclei emitting intense light • can be 100 x entire galaxy! • Incredibly compact: < size of Solar System • “Nonstellar” (“nonthermal”) spectrum of radiation • Spectral lines smeared out in wavelength • interpret by Doppler shiftatoms move at ~10% c • randomly moving gas clouds, not thermal motion • High-speed jets of gas • close to speed of light

  2. Carbon Hydrogen Oxygen ULTRAVIOLET SPECTRUM of a SEYFERT GALAXY NGC 4151: Digital Sky Survey UV spectrum of the Seyfert galaxy NGC 4151 observed with Hopkins UV Telescope (Kriss et al. 1992)

  3. NGC 1068: An Obscured Seyfert This bright cloud has a direct view of the intense nucleus Radiation and (possibly) a wind escapes through a cone-shaped funnel Nucleus is hidden in here

  4. Schematic of an AGN C.M. Urry and P. Padovani

  5. MAX. SIZE FROM VARIABILITY The “light travel time” argument: • Suppose source doubles (or halves) brightness in 1 day • If source is bigger than 1 light-day then no signal can coordinate the variation • Therefore source must be be smaller than 1 light-day 1 light-day A catch: Random (uncoordinated) fluctuations may make source appear to vary more quickly than light travel time - but only rarely.

  6. THE REAL CATCH:RELATIVISTIC MOTION • Suppose source emits flashes 1 day apart, while moving toward you at Flash 1 0.2 lt-day Flash 1 Flash 2 1 lt-day Flash 2 0.8c Flashes emitted 1 day apart, received 0.2 days apart. 0.8 lt-day Flash 1 Day 1 Day 0

  7. MIN. MASS FROMENERGY OUTPUT • We see lots of active galaxies • Their lives can’t be too short (> few million yr) • Luminosity X Lifetime = Total energy output • Total energy output < Total mass • “Central Engine” > few million solar masses

  8. PUTTING IT TOGETHER • Variability small size • Energy output large mass COMBINATION OF SMALL SIZE AND LARGE MASS BLACK HOLE

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