Take the 2-minute tour ×
Astronomy Stack Exchange is a question and answer site for astronomers and astrophysicists. It's 100% free, no registration required.

If we consider a point on the central part of a contracting object as observed from earth, the point is continuously moving away from us as the object contracts. Moreover, light emerges from a deeper gravitational well as the object contracts. So, shouldn't contracting objects show a redshift? And if so it should be less towards the edges than towards the centre, right?

share|improve this question
What do you mean by central part of the contracting object? 'Earth expands'? Where is the light emerging from? –  polyphant May 1 at 18:00
@ChrisLovell I mean as viewed from the earth, a spherical object would appear circular. So, the part we see as the center of that apparent circle would be moving away faster in the direction opposite to us. –  Yashbhatt May 2 at 2:39
The earth expands?? –  Py-ser May 2 at 3:16
Sorry, typed the question late at night. Made the edits. –  Yashbhatt May 2 at 3:23

1 Answer 1

up vote 2 down vote accepted

shouldn't contracting objects show a redshift?

Yes, they should. But do they, actually? That's the better question.

To have any appreciable redshift, the speed of the object needs to be huge. That will be a very short implosion. Also, there aren't many mechanisms that can accelerate implosions that much.

What I'm saying is - it's theoretically possible, but in practice you won't see it that often, if ever.

And if so it should be less towards the edges than towards the centre, right?

Sure. If the object is transparent to its own radiation, then you'd see blueshift from the other side, too. Again, this is very theoretical.

share|improve this answer
"in practice you won't see that often" . Has anyone ever observed such a thing? –  Yashbhatt May 2 at 2:41

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.