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Unformatted text preview: 2. H o = 70 km/s/Mpc. What would be the apparent diameter (in arcseconds) of a galaxy which has an actual diameter of 60 kpc if its 656.3 nm H line is observed at 740 nm. Solution: redshift=Δλ/λ=(740656.3)nm / 656.3nm = 0.128 = v/c v = 300000 km/s * 0.128 = 38400 km/s d = v/Ho = 38400 km/s / 70 km/s/Mpc = 549 Mpc. 60 kpc = 549 000 kpc x apparent d. / 57.3 o . app d = 0.006 o = 22.5'' 3. A quasar with a luminosity of 10 39 W has 5x10 8 M of material in its accretion disk. Assuming constant luminosity and 10% efficiency, how long would this quasar consume its fuel? Solution: Total massenergy of the accretion disk, E tot = mc 2 = 5 x 10 8 x 2 x 10 30 kg x 9 x10 16 m/s = 9 x 10 55 J efficiency is 10%, then the total energy that can be radiated away is E rad = E tot * 0.1 = 9x10 54 J power radiated away per second by the quasar is P rad = 10 39 J/s Then time = E rad /P rad = 9 x 10 15 s = 300 million years...
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 Fall '09
 MehmetYali
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