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Chapter 25: Problem 9

Why were some astronomers skeptical that the redshifts of quasars gave a true indication of their distance?

Short Answer

Expert verified
Some astronomers were skeptical that the redshifts of quasars accurately indicated their distance because these quasars displayed unusually high redshifts, implying that they were extremely far away and extraordinarily bright - much more than any known object. This challenged the existing theories about the limits of brightness and energy for celestial bodies. Moreover, some observed associations of high redshift quasars with low redshift galaxies raised questions about the validity of redshift-based distance estimation.

Step by step solution

01

Understand Redshift

Redshift in astronomy corresponds to the change in observed wavelength and frequency due to the relative motion between the observer and the source. It follows from the Doppler effect in light. When the source of light is moving away from the observer, the light appears ‘redder,’ or shifted towards longer wavelengths, than when it is at rest. This is called redshift.
02

Hubble's Law & Distance Estimation

Hubble's law is used to estimate the distance of celestial bodies. According to Hubble's law, the redshift (z) of light from a distant galaxy is proportional to its distance from the observer, because the space between is expanding. The greater the redshift, the further away the galaxy is.
03

Why Some Astronomers Were Skeptical

Quasars showed very high redshifts, suggesting they were extremely distant and therefore extraordinarily bright and powerful, much more so than any known object in the universe. Some astronomers were skeptical because such extreme properties challenged existing theories about the energy production and capacity of celestial objects. There were also some apparent inconsistencies, such as quasars with high redshifts found in proximity to galaxies with low redshifts.

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Most popular questions from this chapter

. What is a blazar? What is unique about its spectrum? How is it related to other active galaxies?

Use a telescope with an aperture of at least \(20 \mathrm{~cm}\) (8 in.) to observe the Seyfert Galaxy NGC 1068 (also known as M77). Located in the constellation Cetus (the Whale), this galaxy is most easily seen from September through January. The epoch 2000 coordinates are R.A. \(=2^{\mathrm{h}} 2.7^{\mathrm{m}}\) and Decl. \(=-0^{\circ} 01^{\prime}\). Sketch what you see. Is the galaxy's nucleus diffuse or starlike? How does this compare with other galaxies you have observed?

Relativistic Redshift. Access the Active Integrated Media Module "Relativistic Redshift" in Chapter \(2.5\) of the Universe Web site or eBook. Use this to calculate the redshift and recessional velocity of quasar in whose spectrum the \(\mathrm{H}_{\mathrm{\alpha}}\) emission line of hydrogen (unshifted wavelength \(656 \mathrm{~nm}\) ) appears at a wavelength of (a) \(937 \mathrm{~nm}\) and (b) \(5000 \mathrm{~nm}\).

Suppose you saw an object in the sky that you suspected might be a quasar. What sort of observations might you perform to test your suspicion?

The quasar SDSS 1044-0125 has a redshift \(z=5.80\). At what speed does this quasar seem to be receding from us? Give your answer in \(\mathrm{km} / \mathrm{s}\) and as a fraction of the speed of light \(c\).
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