HW6-solutions

# HW6-solutions - Phys133 Written HW#6 SOLUTIONS IN RED...

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Phys133 Written HW#6 SOLUTIONS IN RED FONT ------------------------------------------------------------------------- Object at center of Active Galaxy M84 Figure 1 displays a Hubble Space Telescope slit spectrum taken of the nucleus of the active galaxy M84. It shows the Doppler shift of gas orbiting the galaxy ʼ s center. 1. From the right-side velocity plot, read off an estimated value for the recession speed Vc of the center of the galaxy. Give this in km/s. The dotted line representing the center velocity is roughly at V=1100 km/s. 2. Assuming this galaxy-center velocity is due to expansion of the universe, estimate the distance D to this galaxy (in Mpc) if the Hubble constant is taken to have a value Ho = 70 km/s/Mpc. Vc = Ho D => D = Vc/Ho = 1100 (km/s) / 70 (km/s/Mpc) = 15.7 Mpc 3. About how many years does it take light from this galaxy to reach earth? 1 pc = 3.26 light years => D= 3.26 * 15.7 Mly = 51 Mly So it takes light 51 Million years to reach earth. 4. From the graph, read off the peak change in speed Delta V toward and away from us on either

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HW6-solutions - Phys133 Written HW#6 SOLUTIONS IN RED...

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