Question

(a) Galaxies emit electromagnetic radiation from the transition of electrons between different atomic orbits in hydrogen. One such transition is called the Lyman-α transition. When this transition occurs in hydrogen in the lab it produces light with wavelength λemit = 121.567 nm. This transition has been observed in one of the most distant objects ever seen, called a quasar. The observed wavelength of the Lyman-α transition from the quasar is λobs = 866.0 nm. What is the redshift of the quasar?

b) The quasar is moving away from us. Using the formula for the Doppler shift of light, show that the velocity of the source can be written in terms of the redshift.

(c) What is the speed of recession of the quasar?

(d) It is found that distant galaxies are moving away from us with a speed proportional to their distance from us, v = H0d, where H0 is called Hubble’s constant. The quasar is at a distance of about 4000 Mpc (1 Mpc, or megaparsec, is about 31×1021 m). What is Hubble’s constant?

(e) An excellent estimation of the age of the Universe is t0 = 1 H0 . What is this value in years?

Answer 1