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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?

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  • $\begingroup$ Non-spinning black holes are a theoretical ideal that is unlikely to be found in nature.astronomy.stackexchange.com/questions/11626/… $\endgroup$
    – Marijn
    Aug 14 '16 at 9:35
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    $\begingroup$ The Universe itself doesn't spin. Except sunday mornings. :-) $\endgroup$
    – peterh
    Aug 14 '16 at 11:23
  • $\begingroup$ 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. $\endgroup$ 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.

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    $\begingroup$ 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. $\endgroup$
    – Pathfinder
    Feb 14 '20 at 18:45
  • $\begingroup$ @Pathfinder I described both options: tidally locked bodies that technically do spin (as you describe) and bodies that don't spin at all. $\endgroup$
    – user30007
    Feb 14 '20 at 19:58
  • $\begingroup$ 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 ;) $\endgroup$
    – 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/

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  • $\begingroup$ Thanks, does this explanation apply also to elementary particles, or there are other reasons? $\endgroup$
    – user13628
    Aug 14 '16 at 13:22
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    $\begingroup$ @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". $\endgroup$ Aug 14 '16 at 14:49
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    $\begingroup$ 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. $\endgroup$
    – Thriveth
    Aug 15 '16 at 14:12
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    $\begingroup$ 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. $\endgroup$
    – zephyr
    Aug 15 '16 at 16:03
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    $\begingroup$ Not to mention, this is a pretty flawed explanation of the Big Bang. $\endgroup$ Aug 16 '16 at 20:00

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