1. Distance:
* Cosmological Redshift: This is the most significant factor. As light travels through the expanding universe, the space itself stretches, causing the wavelengths of light to be stretched as well. This stretching results in a redshift, and the further the galaxy, the more the space has expanded, leading to a larger redshift. This is known as Hubble's Law, which states that the redshift of a galaxy is directly proportional to its distance.
2. Relative Velocity:
* Doppler Redshift: This occurs when a galaxy is moving away from us. The light waves emitted by the galaxy are stretched due to the relative motion, resulting in a redshift. This effect is similar to the Doppler effect we observe with sound waves, where the pitch of a siren changes as it moves towards or away from us.
Other factors that can contribute to redshift, though less significant, include:
* Gravitational Redshift: This effect occurs due to the curvature of spacetime caused by gravity. Light from a galaxy in a strong gravitational field can be redshifted as it escapes the field. However, this effect is generally much smaller than cosmological redshift.
* Intrinsic Redshift: This is a theoretical redshift caused by the internal properties of the galaxy itself, like its internal velocity or the presence of dark matter. However, this effect is not well understood and is currently considered negligible compared to cosmological redshift.
In summary, the primary factor determining redshift in light from a galaxy is its distance, due to the expansion of the universe. Relative velocity can also contribute to redshift, but its effect is usually much smaller than cosmological redshift.
