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Lecture 35 – Extragalactic Astronomy

Lecture 35 – Extragalactic Astronomy. Summary so far. More general formula for the redshift. Reason: If d = 1000 Mpc, then v = H 0 d gives v = 70,000 km/sec = 0.25 c. More distant galaxies have v > c? What’s up?. Figure 24.3. An interlude…Radio Astronomy…will make sense later.

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Lecture 35 – Extragalactic Astronomy

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  1. Lecture 35 – Extragalactic Astronomy Summary so far

  2. 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? What’s up? Figure 24.3

  3. An interlude…Radio Astronomy…will 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

  4. The Radio Sky Radio sources – many associated with giant elliptical galaxies

  5. Radio Galaxies, e.g. 3C296 Radio galaxies “shine” by a mechanism called synchrotron radiation

  6. What is synchrotron radiation? Accelerated electrons radiate EM waves DEMO

  7. 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

  8. 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

  9. With Hubble Space Telescope, we have imaged Quasars

  10. 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

  11. Question: what does this mean? 7236 quasars

  12. The slide with no name

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