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ACTIVE GALACTIC NUCLEI

Discover the enigmatic world of Active Galactic Nuclei, ultra-compact light sources at the cores of galaxies, emitting nonstellar radiation with high-speed gas jets and hidden nuclei. Dive into the Ultraviolet Spectrum of Seyfert Galaxies like NGC 4151 and NGC 1068, and unravel the mysteries of these celestial powerhouses. Learn about the light travel time argument and the impacts of relativistic motion on observational variances. Explore the implications of energy output and mass in the context of active galaxies to reveal the presence of supermassive black holes.

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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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