Hydrogen atoms have a spectral line with a wavelength of 656 nm. Suppose we observe this particular line from hydrogen gas located near the event horizon of a black hole. Assuming the gas has no motion toward or away from us, where would this line appear in the spectrum?

Question

A) at a wavelength larger than 656 nm
B) at a wavelength shorter than 656 nm
C) at the same wavelength of 656 nm that we observe for this line in the laboratory
D) We could not record a spectrum from this gas because its light would be sucked into the black hole and therefore would never reach Earth.

Answer 1

A) at a wavelength larger than 656 nm