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Chapter 34: Q5PE (page 1238)

On average, how far away are galaxies that are moving away from us at\({\rm{2}}{\rm{.0 \% }}\)of the speed of light?

Short Answer

Expert verified

The direction is obtained as: \(d{\rm{ = 300 Mly}}\).

Step by step solution

01

Recession velocity

The recession velocity for a galaxy is given by,

\(v = {H_o}d\)

Here\({H_o}\)is the Hubble constant and\(d\)is the distance to the galaxy.

02

Evaluating the direction

Galaxies are moving away from \({\rm{2\% c}}\)at distance.

\(\begin{array}{c}d = \frac{v}{{{H_0}}}\\ = {\rm{ }}\frac{{{\rm{0}}{\rm{.2 \times 3 \times 1}}{{\rm{0}}^{\rm{8}}}\,{\rm{m/s}}}}{{{\rm{20 km/sMly}}}}\\ = {\rm{ 300 Mly}}\end{array}\)

Therefore, the distance of the galaxies that are moving away from us at \(2\% \) of the speed of the light is \(300\,{\rm{Mly}}\).

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Most popular questions from this chapter

Does observed gravitational lensing correspond to a converging or diverging lens? Explain briefly.

Suppose you measure the red shifts of all the images produced by gravitational lensing, such as in figure below. You find that the central image has a red shift less than the outer images, and those all have the same red shift. Discuss how this not only shows that the images are of the same object, but also implies that the red shift is not affected by taking different paths through space. Does it imply that cosmological red shifts are not caused by traveling through space (light getting tired, perhaps)?

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