Spiral galaxies

[Alanh]

Do all spiral galaxies spin the same direction? Is there any rule for this?

[Chris Peterson]

Do all spiral galaxies spin the same direction? Is there any rule for this?

In most spiral galaxies the arms trail the rotation direction. But in a few they appear to lead. The actual direction a galaxy rotates is purely a function of our point of view, with about half going each way... it just depends whether we see them from the "top" or the "bottom" side (with those terms themselves being arbitrary).

[neufer]

Galaxy pairs follow filaments
Keith T. Smith
Science 14 Dec 2018:
Vol. 362, Issue 6420, pp. 1260-1261
DOI: 10.1126/science.362.6420.1260-a

<<Galaxies are nonuniformly distributed in the Universe, forming a cosmic web of filaments and clusters. Filaments occupy about 5% of the volume of the Universe but contain about a third of the galaxies, which grow by merging. Mesa et al. identified pairs of neighboring galaxies embedded within filaments. They found that the orientation of the pairs preferentially align with the axes of the surrounding filaments, with the effect being more pronounced for elliptical galaxies than for spirals. Because galaxy spins are known to follow the filament direction, this implies that major merger events have a preferred orientation in this environment.>>

2dF survey map, containing the SDSS Great Wall

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<<In physical cosmology, galaxy filaments (subtypes: supercluster complexes, galaxy walls, and galaxy sheets) are the largest known structures in the universe. They are massive, thread-like formations, with a typical length of the order of 200 to 500 million light-years that form the boundaries between large voids in the universe. Filaments consist of gravitationally bound galaxies. Parts wherein many galaxies are very close to one another (in cosmic terms) are called superclusters. In the standard model of the evolution of the universe, galactic filaments form along and follow web-like strings of dark matter. It is thought that this dark matter dictates the structure of the Universe on the grandest of scales. Dark matter gravitationally attracts baryonic matter, and it is this "normal" matter that astronomers see forming long, thin walls of super-galactic clusters.>>

[orin stepanek]

This thread is not an APOD; Shouldn't it be in The Asterisk Café: (Discuss Anything Astronomy Related)!

[bystander]

This thread is not an APOD; Shouldn't it be in The Asterisk Café: (Discuss Anything Astronomy Related)!

You are correct, sir!

[Alanh]

Thank you.