In the chapter, we discussed that the largest redshifts found so far are greater than 6. Suppose we find a quasar with a redshift of 6.1. With what fraction of the speed of light is it moving away from us?

The quasar is moving with 0.93 the speed of light.

Explanation:

Let:

v be the speed that the quasar is moving at away from us,

z be the redshift

c be the speed of light.

The relativistic doppler shift formula, the fraction of the speed of light that the quasar is moving away from us is given by:

v/c = [ (z - 1) ^2 - 1]/[ (z - 1) ^2 + 1]

= [ (6.1 - 1) ^2 - 1]/[ (6.1 - 1) ^2 + 1]

= 0.93

v = 0.93*c

Therefore, the quasar is moving with 0.93 the speed of light.