Question

Imagine two particles of dust, A and B, are inside an accretion disk of a black hole. Particle A is closer to the black hole and particle B is further from the black hole. If they were the same temperature and emitted the same light, how would their colours compare to you as a distant observer?

a) Particle A appears bluer
b) Particle B appears bluer
c) Both appear the same
d) Both appear red

Answer 1

Particle A would appear redder to a distant observer due to a greater gravitational redshift compared to Particle B, which is further from the black hole and experiences less of this effect.

Step-by-step explanation:

The colors of two particles of dust, A being closer to the black hole and B being further away, as observed from a distance, will be affected by the gravitational field of the black hole. As hot matter falls into a black hole, it emits radiation due to high temperatures and velocities.

The phenomenon of gravitational redshift occurs when light from particle A, which is closer to the black hole, travels to a distant observer, causing the light to shift to longer, redder wavelengths. Hence, particle A will appear redder because its light is more redshifted compared to particle B, which is further away and experiences less gravitational redshift.

Particle A would appear redder due to the gravitational redshift, an effect predicted by the theory of General Relativity, which makes it more challenging to observe radiation from matter near the black hole.