Just because we observed that our milky way galaxy is spinning in a certain direction therefore we assume it is applicable to all other galaxies, I am curious to find out if hypothetically most of the celestial objects such as natural satellites, planets, stars even galaxies within our observable universe are spinning/rotating in the same direction as the milky way what kind of implications can we say about the condition in the early universe? or is it just an coincident?
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$\begingroup$ I'm very astronomy-naive, but if viewed "upside down", isn't each body already spinning in the opposite direction? $\endgroup$– NicoleCommented Nov 4, 2015 at 7:58
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1$\begingroup$ I think what you are asking is is there any non-randomness in the direction of angular momentum vectors? $\endgroup$– ProfRobCommented Nov 4, 2015 at 8:01
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$\begingroup$ @RobJeffries: yes $\endgroup$– user6760Commented Nov 4, 2015 at 8:05
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2$\begingroup$ This property of spirals is referred to as the handedness of the their rotation, and has been investigated by several authors, e.g. Trujillo et al. (2006) and Longo (2009, 2011), who seem to find a small, but significant, parity violation. I don't know enough about the subject to comment on the credibilty of the studies, though. $\endgroup$– pelaCommented Nov 4, 2015 at 8:52
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2 Answers
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Angular momentum of the entire universe remains constant. Assuming that the big bang was the only thing present initially, it wouldn't posses any angular momentum. Now, if there are unequal number of planets, galaxies, stars,etc. in the observable universe spinning in both directions, there'd be some net angular momentum which would violate the conservation of angular momentum. Hence, in my opinion, there are equal number of celestial bodies spinning in both directions.
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Galaxies are oriented in different directions, if we consider the orientation to be relative to their central axis of rotation. Then when we consider things like galaxies and their "direction" of spin, we tend to orient them so that "up" is the direction that, when we look at them from "above", they rotate in an anticlockwise direction - the same as observing Earth's rotation looking down from the North Pole. We tend to use a "right-hand rule" for this rotation, so that when the direction of rotation matches the curl of the fingers on the right hand, the thumb points in the "up" direction. What this means is that every galaxy rotates the same way.
On the smaller scale what we see is that things in systems tend to rotate in the same direction - looking "down from above" on our Solar System we see that the planets all revolve in the same direction around the Sun (anticlockwise). The vast majority of smaller bodies also revolve in this same direction. The Sun rotates in this same direction. And the planets themselves tend to rotate in the same direction (exceptions being Venus and Uranus). This is understandable as the accretion disc would have been rotating during Solar System formation.
So yes, for the most part at least, as far as we have been able to determine, everything spins the same way within its own environment.
