5

Galaxies consist of dark matter, stars, and gas. While gas is "collisional", i.e. it may interact hydrodynamically and cool, dark matter and, effectively, stars are collisionless. Hence, it is relative easy for an originally more or less spherical, gas-rich galaxy to collapse along the axis of rotation, while centrifugal forces prevents to collapse ...


3

The dynamics of the Solar System and the chemistry of the Solar System bodies don't support a hypothesis of a stellar merger later than formation of the protoplanetary disk which would have mixed-up things considerably and heavily disrupt any circumstellar disk. Thus this basically excludes any collision after the time one can start talking about a protostar,...


1

Stellar mergers are certainly possible, but also relatively rare. Maybe protostars merging is a bit more common since they have less relative velocity. However, unless the merger is straight it will typically deposit a lot of angular momentum. The sun seems to be a slow rotator for its spectral class. Hence it is not likely it was formed through a stellar ...


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