"The answer is an effect from Einstein’s General Theory of Relativity called the 'gravitational redshift...' "
<<https://www.nasa.gov/image-article/einsteins-theory-of-relativity-critical-gps-seen-distant-stars/ >>
Your above comment represents a definitive answer to the original question, which is not and needs to be looked at differently. As you note from NASA's observation, "The answer is an effect from Einstein’s General Theory of Relativity called the “gravitational redshift ..." The statement appears to be relativistic bias, because the redshift in light is not the only significance. There are many and not only 'gravitational red shift'. The observations posted by NASA do not reveal the full picture of redshift, and "gravitational redshift" is not the only significant cause of redshift in light.
Redshift is a natural phenomenon caused by various causes, and not significantly due to gravitational redshift, here is a list of causes of redshift in light.
1. Propagation Delay or, Time Delay: First and foremost light should cause its own propagation delay or transmission delay or time delay. Propagation delay is the amount of time required for a signal to be received with light after it is sent; This is caused by the time it takes for the signal to travel through a medium or void in space. Propagation delay is of primary interest in electronic circuit design and computer networking, although all signals will inherently experience some form of propagation delay. As light travels a distance of 1 km in a vacuum, there will be a time delay or delay of 3.33 microseconds (µsec). Time delay (Δt) corresponds to wavelength enlargement Δλ as we know t ∝ 1/f or t ∝ λ. This increase in wavelength will cause a red shift as it accumulates over time.
2. Doppler redshift: As an object moves away from the observer, the light waves emitted by the object are enlarged, causing them to have a lower pitch and moving them towards the red end of the electromagnetic spectrum, where the wavelength of light is longer (λ+Δλ). Blue shift occurs when the phenomenon described above is reversed.
3. Gravitational Redshift: The phenomenon that electromagnetic waves or photons escaping a gravitational well expend their energy resulting in longer wavelengths (λ+Δλ), which shifts the frequency of light towards the red end of the electromagnetic spectrum resulting in gravitational redshift.
4. Photometric Redshift: Photometric redshift is an estimate of the deceleration velocity of an astronomical object such as a galaxy or quasar, where Doppler redshift can replace the deceleration velocity.
5. Cosmic Redshift: The universe is expanding, and that expansion stretches light through interstellar space in a phenomenon known as cosmic redshift. The higher the redshift, the more distance the light has travelled.
By this time, you probably understand why NASA's observation of “gravitational redshift", not just redshift as you seem to present in the existence of different redshifts.
The final redshift is calculated based on the effective redshift, and in this context, one can see my research papers available on my ResearchGate profile.
Besides. Relativistic time or time dilation is not redshift. As time distortion can cause in objects with mass but redshift causes in electromagnetic waves having massless photons.
