Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Lewis Thomson on 06/09/2022 14:43:00
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Listener David wrote into the Naked Scientists to ask this question.
"According to red/blue shift theory stars nearer to us are moving away at a slower rate than those further away. Is this correct?"
Discuss your thoughts in the comments below...
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According to red/blue shift theory stars nearer to us are moving away at a slower rate than those further away.
There is no red/blue shift theory. The redshift of distant objects (galaxies, not so much individual stars, the vast majority of which cannot be individually picked out) is an observation, not a speculation. So that needed to be explained, which can be done so with a theory that has expansion of space, called the big bang theory. If everything is moving away, then if you extrapolate backwards, one can imagine everything was nearby about 14 billion years ago, and the theory suggests exactly that.
So yes, we observe distant objects moving away from us at a rate proportional to their distance from us, with minor local variances in that speed. Due to this expansion, our local group of galaxies (us and Andromeda plus a bunch of little ones) will never merge with any other group despite the gravitational attraction of some really massive 'nearby' objects such as the Virgo supercluster.
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To expand a bit on Halc said:
while the universe on a whole is expanding, smaller structures within in it are not, as they are bound together by gravitational attraction. The individual stars we see in the sky are part of our own galaxy, which is one of those bound structures. Even the local group of neighboring galaxies are a part of a bound structure. It isn't until you go out to much larger scales that the expansion dominates and you see the increasing red shift with distance.
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I would add: This doesn't just apply to us.
Pick any of those distant galaxies you can see with the Hubble telescope. If you were there, you would also see
distant objects moving away from us at a rate proportional to their distance from us, with minor local variances in that speed
So we aren't special in that regard.
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Are stars nearer to Earth moving slower than stars further away?
It all depends on the frame of reference.
In a star's own frame of reference, it isn't moving at all. That applies to our Sun, and both near and further-away stars.