I have a vague recollection of theoretical stellar encounters that left a star going relativistic but I'll leave that for you'all to google ( and it's not observed, merely theoretical ).
2.
Most roughly orbit a galaxy in the same direction, but some could orbit in retrograde ( likely as a result of a previous close encounter with another star ) and a galactic collision would greatly raise the odds of a stellar encounter-- though the odds remain extremely low.
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