Radio Galaxies and Quasars
Powerful natural radio transmitters associated withGiant elliptical galaxies
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The discovery of quasars: a history lesson that teaches something about the universe
Some of the brightest radio sources, 3C48, 3C273, did not seem to be associated with
galaxies, but with star-like objects
Spectra of quasars showed strong emission lines, highly redshifted
See Figure 24.2 of text
Application of Hubble’s Law indicates enormously distant,Brilliant objects. But where are the galaxies?
Summary of Quasar Characteristics
• Clearly are a brilliant, energetic phenomenon in centers of galaxies
• Quasars are very distant. We see them as they were long ago
• Let’s look at the distribution of quasar redshifts
Observations of quasars and radio galaxies allow us to look out billions of light years
into space• NVSS survey of the sky at radio
wavelengths found 1.8 million sources, almost all of which are radio galaxies and quasars
• The Sloan Digital Sky Survey (SDSS) measured positions, brightness, and spectra (therefore distances) of 675,000 galaxies and 90,000 quasars
• What do we see? What is the shape of the universe as a whole?