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Universe Eighth Edition

Roger A. Freedman • William J. Kaufmann III. Universe Eighth Edition. CHAPTER 25 Quasars and Active Galaxies. 25-1 The distinctive features of quasars 25-2 The connection between quasars and distant galaxies 25-3 What Seyfert galaxies and radio galaxies are and how they compare to quasars

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Universe Eighth Edition

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  1. Roger A. Freedman • William J. Kaufmann III Universe Eighth Edition CHAPTER 25 Quasars and Active Galaxies

  2. 25-1 The distinctive features of quasars 25-2 The connection between quasars and distant galaxies 25-3 What Seyfert galaxies and radio galaxies are and how they compare to quasars 25-4 The properties of active galactic nuclei 25-5 How supermassive black holes can power active galactic nuclei 25-6 Why many active galaxies emit ultrafast jets of material By reading this chapter, you will learn

  3. Key Ideas • Quasars: A quasar looks like a star but has a huge redshift. These redshifts show that quasars are several hundred megaparsecs or more from the Earth, according to the Hubble law. • To be seen at such large distances, quasars must be very luminous, typically about 1000 times brighter than an ordinary galaxy. • About 10% of all quasars are strong sources of radio emission and are therefore called “radio-loud”; the remaining 90% are “radio-quiet.” • Some of the energy emitted by quasars is synchrotron radiation produced by high-speed particles traveling in a strong magnetic field.

  4. Key Ideas • Seyfert Galaxies: Seyfert galaxies are spiral galaxies with bright nuclei that are strong sources of radiation. Seyfert galaxies seem to be nearby, low-luminosity, radio-quiet quasars. • Radio Galaxies: Radio galaxies are elliptical galaxies located midway between the lobes of a double radio source. • Relativistic particles are ejected from the nucleus of a radio galaxy along two oppositely directed beams.

  5. Key Ideas • Blazars: Blazars are bright, starlike objects that can vary rapidly in their luminosity. They are probably radio galaxies or quasars seen end-on, with a jet of relativistic particles aimed toward the Earth. • Active Galaxies: Quasars, blazars, and Seyfert and radio galaxies are examples of active galaxies. The energy source at the center of an active galaxy is called an active galactic nucleus. • Rapid fluctuations in the brightness of active galaxies indicate that the region that emits radiation is quite small.

  6. Key Ideas • Black Holes and Active Galactic Nuclei: The preponderance of evidence suggests that an active galactic nucleus consists of a supermassive black hole onto which matter accretes. • As gases spiral in toward the supermassive black hole, some of the gas may be redirected to become two jets of high-speed particles that are aligned perpendicularly to the accretion disk. • An observer sees a radio galaxy when the accretion disk is viewed nearly edge-on, so that its light is blocked by a surrounding torus. At a steeper angle, the observer sees a quasar. If one of the jets is aimed almost directly at the Earth, a blazar is observed.

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