What primarily causes the redshift observed in very distant galaxies across vast intergalactic distances?

Answer

The stretching of space between the galaxy and the observer

For distant galaxies, cosmological redshift occurs because the space itself stretches over billions of years, stretching the light traveling through it toward longer wavelengths.

What primarily causes the redshift observed in very distant galaxies across vast intergalactic distances?
galaxiesastronomyuniverseredshiftblueshift