Concept explainers
All galaxies farther away than about
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- The classical Doppler shift for light. A light source recedes from an observer with a speed v that is small compared with c. (a) Show that in this case, Equation 1.15 reduces to ffvc (b) Also show that in this case vc (Hint: Differentiate f = c to show that / = f/f) (c) Spectroscopic measurements of an absorption line normally found at = 397 nm reveal a redshift of 20 nm for light coming from a galaxy in Ursa Major. What is the recessional speed of this galaxy?arrow_forwardAll galaxies farther away than about exhibit a red shift in their emitted light that is proportional to distance, with those farther and farther away having progressively greater red shifts. What does this imply, assuming that the only source of red shift is relative motion?arrow_forwardSome of the familiar hydrogen lines appear in the spectrum of quasar 3C9, but they are shifted so far toward the red that their wavelengths are observed to be 3.0 times as long as those observed for hydrogen atoms at rest in the laboratory. (a) Show that the classical Doppler equation gives a relative velocity of recession greater than c for this situation. (b) Assuming that the relative motion of 3C9 and Earth is due entirely to the cosmological expansion of the universe, find the recession speed that is predicted by the relativistic Doppler equation.arrow_forward
- What speed should a galaxy move with respect to us so that the sodium line at 589.0 nm is observed at 589.6 nm?arrow_forwardIf a galaxy is 500 Mly away from us, how fast do we expect it to be moving and in what direction?arrow_forwardBecause of the cosmological expansion, a particular emission from a distant galaxy has a wavelength that is 2.00 times the wavelength that emission would have in a laboratory. Assuming that Hubble’s law holds and that we can apply Doppler-shift calculations, what was the distance (ly) to that galaxy when the light was emitted?arrow_forward
- Quasars are thought to be the nuclei of active galaxies in the early stages of their formation. A typical quasar radiates energy at the rate of 1041 W. At what rate is the mass of this quasar being reduced to supply this energy? Express your answer in solar mass units per year, where one solar mass unit (1 smu = 2.0*10^30 kg) is the mass of our Sun.arrow_forwardIn the laboratory, one of the lines of sodium is emitted at a wavelength of 590.0 nm. In the light from a particular galaxy, however, this line is seen at a wavelength of 602.0 nm. Calculate the distance to the galaxy, assuming that Hubble’s law holds and that the Doppler shift of Eq. 37-36 applies.arrow_forwardSuppose you measure the red shifts of all the images produced by gravitational lensing, .You findthat the central image has a red shift less than the outer images, and those all have the same red shift. Discuss how this not onlyshows that the images are of the same object, but also implies that the red shift is not affected by taking different paths throughspace. Does it imply that cosmological red shifts are not caused by traveling through space (light getting tired, perhaps)?arrow_forward
- How competitive are the constraints on Δα/α compared to quasar observations, and how well constrained is its dependence on the changes in Newtonian potential?arrow_forwardUse the distance and velocity data tofind the rate of expansion as a function of distance.(b) If you extrapolate back in time, how long ago would all ofthe galaxies have been at approximately the same position?The two parts of this problem give you some idea of how theHubble constant for universal expansion and the time back tothe Big Bang are determined, respectivelyarrow_forwardA galaxy is 30 Mpc away from us and has a recession velocity of 2000 km.s-1. What isHubble’s constant based on these values?arrow_forward
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