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CHAPTER [strong]17[/strong]

Artist’s conception of the two-lobed emission of gas, dust, and electromagnetic radiation from the vicinity of a supermassive black hole in the center of a galaxy. The dusty cloud perpendicular to the two lobes is the side view of a disk of gas and dust spiraling inward toward the black hole. Seen from this perspective, the system is called a double-radio source.

Quasars and Other Active Galaxies

WHAT DO YOU THINK?

  • What does “quasar” stand for?
  • What do quasars look like?
  • Where do quasars get their energy?

Answers to these questions appear in the text beside the corresponding numbers in the margins and at the end of the chapter.

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In this chapter we look at active galaxies—energy sources of almost unimaginable power. While the short-lived outputs of supernovae boggle the mind, they represent miniscule amounts of energy compared to quasars, Seyfert galaxies, radio galaxies, and BL Lac objects. Quasars, for example, emit more energy each second than the Sun does in 200 years, and they continue to do so for millions of years. Evidence shows that most galaxies undergo periods of similar activity. Some truly remarkable activity must occur deep within quasars and other ultrahigh energy sources to make them so luminous.

In this chapter you will discover

  • bright and unusual objects called active galaxies
  • distant, luminous quasars
  • the unusual spectra and small volumes of quasars
  • the extremely powerful BL Lac objects
  • supermassive black holes that serve as central engines for radio galaxies, quasars, Seyfert galaxies, and BL Lac objects