Lecture 35 Extragalactic Astronomy

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Lecture 35 Extragalactic Astronomy

• Summary so far

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More general formula for the redshift

• Reason If d 1000 Mpc, then v H0d gives v
  70,000 km/sec 0.25 c. More distant galaxies
  have v c? Whats up?

Figure 24.3
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An interludeRadio Astronomywill make sense later

• To remind you of what you already know.
• Radio astronomy study of universe with EM waves
  having wavelength from about 1 millimeter to 50
  meters
• Comparison optical astronomy studies wavelengths
  between 4E-07 to 7E-07 meters

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The Radio Sky
Radio sources many associated with giant
elliptical galaxies
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Radio Galaxies, e.g. 3C296
Radio galaxies shine by a mechanism called
synchrotron radiation
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What is synchrotron radiation?
Accelerated electrons radiate EM waves DEMO
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History of Radio Astronomy, circa 1960

• Some of the brightest radio sources, 3C48, 3C273,
  did not seem to be associated with galaxies, but
  with star-like objects

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Spectra of these sources showed highly redshifted
lines great distances
Z (w-w0)/w0 0.16, 0.48, 1.7, 4.42 !! Quasar
Quasi-Stellar Radio Sources
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With Hubble Space Telescope, we have imaged
Quasars
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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
• Lets look at the distribution of quasar
  redshifts

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Question what does this mean?
7236 quasars
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The slide with no name