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Do we know of a celestial body which doesn't spin at all on its own axis? If not, why is it so?

  • Non-spinning black holes are a theoretical ideal that is unlikely to be found in nature.http://astronomy.stackexchange.com/questions/11626/how-is-a-non-rotating-black-hole-created – Marijn Aug 14 '16 at 09:35
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    The Universe itself doesn't spin. Except sunday mornings. :-) – peterh Aug 14 '16 at 11:23
  • This is at least a little interesting, as an inertial reference frame is actually an absolute thing, in contrast to most other types of reference frames. – SE - stop firing the good guys Aug 14 '16 at 11:31

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Many red and brown dwarfs must have planets that are in full tidal lock with their host star, that means that the same side of the planet is always facing the star so there is always day while on the other side there is always night. Our Moon and many other moons are also in such a tidal lock with their planet but not with the Sun so that the often-used term "Dark side of the Moon" is verbally incorrect since on the far side there is a day too (when on Earth it is a New Moon).

If you mean non-spinning in the sense that on the same side of the planet it is day for half a year and night the other half I'm quite sure such planets exist too. On SpaceEngine I've seen similar planets. Nothing speaks against the existence of such planets I believe. There also might exist moons whose same side faces their planet for half a year and the other half faces away from it.

user30007
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    Are you implying that tidally locked bodies do not spin? Because they do - In the case of the moon exactly one time for every full orbit around earth. – Pathfinder Feb 14 '20 at 18:45
  • @Pathfinder I described both options: tidally locked bodies that technically do spin (as you describe) and bodies that don't spin at all. – user30007 Feb 14 '20 at 19:58
  • I see, my misunderstanding. But regarding your second example you could argue that even these planets / bodies are spinning around the center of mass they share with whatever they are orbiting. Not sure though about the exact definition of "spin", not a physicist. Nice try though ;) – Pathfinder Feb 18 '20 at 18:02
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Every object in the universe--from a basic star to an exotic black hole--spins, and the origin of that spin can be traced back to the very beginning of time. Within instants after the Big Bang, the primordial fireball of energy expanded at an incredible speed, then later cooled and solidified into all the matter in the universe. Had this fireball been uniform in all directions, everything we see today would be completely homogeneous.

http://www.scientificamerican.com/article/what-causes-objects-such/

Marijn
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  • Thanks, does this explanation apply also to elementary particles, or there are other reasons? –  Aug 14 '16 at 13:22
  • All elementary particles have intrinsic spin associated with them. If we look for a mechanism that links the cosmic angular momentum with the quantum momenta of the constituent elementary particles that make up the object, we will run into trouble, see: http://sciexplorer.blogspot.nl/2014/11/why-do-particles-have-spin_18.html – Marijn Aug 14 '16 at 13:30
  • Thanks, you know that bugs me! I don't get why they deny particles spin, since that seems a fundamental feature of ohysics. Just the fact that the value of L is a little larger than the expected, doesn't mean that they sit still. The fact that L is 500 times bigger could have dozens of explanations, and that would have intrinsic origin, don't you agree? –  Aug 14 '16 at 13:34
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    @user104372 Particles don't actually spin, just as they don't have position or size. However, they do have angular momentum, which is what we call their "spin". – Sir Cumference Aug 14 '16 at 14:49
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    Downvoted, the idea of the "primordial fireball" is very misleading, and it does not actually explain by which mechanisms this supposed fireball would set "everything" in motion. – Thriveth Aug 15 '16 at 14:12
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    I don't understand this answer. What does the initial expansion of the universe have to do with the angular momentum of objects that formed after that point? And what is meant by "had this fireball been uniform in all directions, everything we see today would be completely homogeneous." The "fireball" was uniform in all directions and everything is homogeneous (down to quantum oscillations). Just look at the CMB. In any case, none of that has any relation to spinning stars and black holes. – zephyr Aug 15 '16 at 16:03
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    Not to mention, this is a pretty flawed explanation of the Big Bang. – Sir Cumference Aug 16 '16 at 20:00