Question

How do we know that there are intergalactic clouds between a distant quasar and us?

A) We see hydrogen emission lines at redshifts smaller than that of the quasar.
B) We see hydrogen absorption lines at redshifts smaller than that of the quasar.
C) We see hydrogen emission lines at redshifts greater than that of the quasar.
D) We see hydrogen absorption lines at redshifts greater than that of the quasar.
E) We see that the emission lines from the quasar are lessened by intervening gas and dust.

Answer 1

To determine the presence of intergalactic clouds between a distant quasar and us, we look for hydrogen absorption lines that are redshifted less than the quasar's spectral lines, indicating matter that is closer to us than the quasar.

Step-by-step explanation:

The presence of intergalactic clouds between a distant quasar and us is confirmed by observing hydrogen absorption lines at redshifts smaller than that of the quasar.

Quasars emit light that travels through the intergalactic medium before reaching us. Along the way, any intergalactic clouds containing hydrogen gas can absorb specific wavelengths of light, corresponding to the hydrogen's electronic transitions. Because these clouds are closer to us than the quasar, they are not moving away from us as rapidly as the quasar is, resulting in absorption lines that are redshifted to a lesser extent than the quasar's own spectral lines.

This effect can be observed as narrow hydrogen absorption lines in the quasar's spectrum at wavelengths that are shorter than we would expect based on the quasar's redshift.