Space itself is actually growing as well as celestial bodies having some relative motion that on average moves away from a common point. The growth in space its

Space itself is actually growing as well as celestial bodies having some relative motion that on average moves away from a common point. The growth in space itself is called inflation. Last time I studied cosmology (university) this was an accepted fact although the precise mechanism that explains this inflation was not agreed upon (scalar field, dark energy etc). I think there is some debate about whether inflation is speeding up or slowing down or how long it has occurred for but AFAIK the concensus is that it is a real thing. To make an analogy, it is as if you had an elastic sheet with objects moving on its surface. The elastic sheet can be expanded which causes the distance between any two fixed points to grow. (it's been many years since I studied physics so any corrections to my comments are appreciated)