Quote:
Originally Posted by bluescope
Still very strange to have bi-directional revolution !
Anyone else have any theories ?
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I am not sure that this changes anything much in the galaxy evolution field, but perhaps makes it a little more complex.
The last few years has seen the bottom up scenario for galaxy evolution favoured, where large galaxies like the milky way being shown to be an aggregation of smaller galaxies merged and swallowed over eons of time.
This evidence would give equal weight to the top down scenario, where large galaxies like our own are the product of the collapse of immense gas clouds early in the universe's history. It seem likely that there were at least 2 of these immense clouds interacting in this early era, before settling down and proceeding to amalgamate lots of smaller already formed galaxies in the time since.
You can imagine a giant gas cloud collapsing and forming a nascent milky way, then colliding with another giant gas cloud that now forms the halo. I imagine the nascent milky way would cannibalise much of the second gas clouds mass and then using it for star formation inside the galactic disk, whilst leaving a fossil gas remnant still orbiting prograde (at least from the solar systems perspective).
With the much younger and smaller universe the milky way would then cannibalise other possibly smaller, possibly larger galaxies in the immediate neighborhood to build the galactic empire. M31 is next, although M31 being much larger would no doubt view it the other way around, as being the cannibal rather than the cannibalee.