Do all galaxies spin in the same direction? © Getty Images

Do all galaxies spin in the same direction?

From angular momentum to dark matter, it’s enough to make your head spin on a cosmic scale.

Asked by: Brian Shimell, Banstead

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If all galaxies formed from the same cloud of spinning material, we might expect their spin directions to be the same. This is similar to the planets of the Solar System, which all spin in the same direction as the proto-planetary cloud from which they formed (except for Venus and Uranus which were probably made to spin in the opposite direction by large impacts).

But, although galaxies do not form from the same cloud of material, they are not randomly distributed in space; they form along ‘filaments’ with ‘voids’ in between. This means that proto-galaxies actually are gravitationally linked in small areas of the Universe and this is probably a result of the distribution of dark matter throughout the Cosmos. The matter in these filaments tends to move in a corkscrew motion towards the area of highest density. The result of this is that there can be a preferential direction of spin for galaxies forming in the same filament, although it also depends on the galaxy’s mass.

Hence, if we look out into the Universe, there can be areas that appear to have a preferential direction for galaxy rotation, but averaged over the whole Universe, their spin direction is actually random.


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