<p>Everything moves.  Entire galaxies move.  Our galaxy is moving towards Andromeda at over 100 km/s and our entire local group is moving towards the great attractor even faster than that.</p>

<p>When a less massive object orbits a more massive one, both move, but the less massive one moves more.  Often the calculation is simplified to make the central body unmoving, but that's a simplification and not accurate.</p>

<p>Our Milkyway has a center of mass with a giant black hole in that region.   If anything in our galaxy didn't move, it would slowly fall into the center.   Stars don't move like that, they move around each other while orbiting within the Milky-Way at high speeds.</p>

<p>Movement, I should add, is defined from a certain point of view, so it's always possible to pick one thing and say "this isn't moving" and that would be correct from that thing's point of view, but that object still sits in spacetime (relatively speaking), and space time defines a force, which (shockingly) moves things, so even if you say "Lets say this object isn't moving", the unevenness of space time will move it.</p>

<p>So, everything moves.   That's a universal law.  </p>

CC BY-SA 4.0
2019-03-15T01:30:42.437Z
2019-03-15T01:30:42.437Z
userLTK
<p>Let's review some things. We know stars usually exist in galaxies. When they are, they orbit a central black hole in the center. </p>

<p>Then, there are rogue stars. They have been ejected out of a galaxy. They must be travelling faster than the galaxy's escape velocity to do that, so they are also moving, but very, very fast. </p>

<p>Now, let's review some basic logic. Are red giants stars? Yes they are. They are stars in the giant phase when the star ceases to fuse H into He and fuses heavier elements, to wit, not in the main sequence anymore. <em>But they are still stars</em>.</p>

<p>Thus, it is safe to say all red giants move. </p>

CC BY-SA 4.0
2019-03-15T02:56:53.300Z
Stars in a galaxy don't orbit the central mass. The central mass usually makes up less than a promille of the total galactic mass.
AtmosphericPrisonEscape
CC BY-SA 4.0
2019-03-15T04:30:03.987Z
@AtmosphericPrisonEscape then what exactly keeps the galaxy together? Black matter is not yet confirmed, and we know that stars do indeed orbit around the center of the galaxy.
Max0815
CC BY-SA 4.0
2019-03-15T04:49:33.220Z
The mass of the galaxy itself keeps the galaxy together. While this might sound like an oxymoron, it is not. Stars inside of galaxies are are exactly that - they orbit inside of a huge mass distribution and not outside of it. This changes their orbits fundamentally, apart from the fact that this mass has rather a disky than a spherically symmetric distribution. Also dark matter, not black matter, has many different lines of evidence pointing to it. See wikipedia.
AtmosphericPrisonEscape
CC BY-SA 4.0
2019-03-16T01:07:40.283Z
@AtmosphericPrisonEscape then what do that black holes in the center do? They don't just sit there. And err, I meant dark matter, not black matter.
Max0815
CC BY-SA 4.0
2019-03-15T01:27:07.413Z
2019-03-15T01:27:07.413Z
Max0815
<p>A friend and I are having a friendly chat about this. They are stars so I'm claiming they still move in orbit. </p>

CC BY-SA 4.0
2019-03-15T01:17:02.827Z
By move, you mean change position is space? Everything in space is moving.
Ingolifs
CC BY-SA 4.0
2019-03-15T16:42:54.467Z
they certainly don't orbit us...
Rory Alsop
CC BY-SA 4.0
2019-03-16T07:00:13.003Z
"Move" relative to what? There's no "motion" per se. It's always relative to some other object. So your question is incomplete. It should be "do they move relative to object XYZ?" Then it could be answered. By the way, before you go there, there's no motion "relative to space". Space is not a thing. You can only move, or not move, relative to a thing. But space is just a whole lot of nothing (no-thing) that allows things to move.
Florin Andrei
<star>
Are red giants stationary or do they move?
Ryan Clarke
# Are red giants stationary or do they move?

(Asked by: username_0 on 2019-03-15)

A friend and I are having a friendly chat about this. They are stars so I'm claiming they still move in orbit.

**Tags:** star

> **Comments:**
> **username_1**: By move, you mean change position is space? Everything in space is moving.  
> **username_2**: they certainly don't orbit us...  
> **username_3**: "Move" relative to what? There's no "motion" per se. It's always relative to some other object. So your question is incomplete. It should be "do they move relative to object XYZ?" Then it could be answered. By the way, before you go there, there's no motion "relative to space". Space is not a thing. You can only move, or not move, relative to a thing. But space is just a whole lot of nothing (no-thing) that allows things to move.  

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## 2 answers

### Answer by username_4 on 2019-03-15. Score: 4

Everything moves. Entire galaxies move. Our galaxy is moving towards Andromeda at over 100 km/s and our entire local group is moving towards the great attractor even faster than that.

When a less massive object orbits a more massive one, both move, but the less massive one moves more. Often the calculation is simplified to make the central body unmoving, but that's a simplification and not accurate.

Our Milkyway has a center of mass with a giant black hole in that region. If anything in our galaxy didn't move, it would slowly fall into the center. Stars don't move like that, they move around each other while orbiting within the Milky-Way at high speeds.

Movement, I should add, is defined from a certain point of view, so it's always possible to pick one thing and say "this isn't moving" and that would be correct from that thing's point of view, but that object still sits in spacetime (relatively speaking), and space time defines a force, which (shockingly) moves things, so even if you say "Lets say this object isn't moving", the unevenness of space time will move it.

So, everything moves. That's a universal law.


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### Answer by username_5 on 2019-03-15. Score: 0

Let's review some things. We know stars usually exist in galaxies. When they are, they orbit a central black hole in the center.

Then, there are rogue stars. They have been ejected out of a galaxy. They must be travelling faster than the galaxy's escape velocity to do that, so they are also moving, but very, very fast.

Now, let's review some basic logic. Are red giants stars? Yes they are. They are stars in the giant phase when the star ceases to fuse H into He and fuses heavier elements, to wit, not in the main sequence anymore. *But they are still stars*.

Thus, it is safe to say all red giants move.

> **Comments:**
> **username_6**: Stars in a galaxy don't orbit the central mass. The central mass usually makes up less than a promille of the total galactic mass.  
> **username_5**: @username_6 then what exactly keeps the galaxy together? Black matter is not yet confirmed, and we know that stars do indeed orbit around the center of the galaxy.  
> **username_6**: The mass of the galaxy itself keeps the galaxy together. While this might sound like an oxymoron, it is not. Stars inside of galaxies are are exactly that - they orbit inside of a huge mass distribution and not outside of it. This changes their orbits fundamentally, apart from the fact that this mass has rather a disky than a spherically symmetric distribution. Also dark matter, not black matter, has many different lines of evidence pointing to it. See wikipedia.  
> **username_5**: @username_6 then what do that black holes in the center do? They don't just sit there. And err, I meant dark matter, not black matter.  

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