Colliding Gasses of Galaxies

The hubble has shown us many galaxies that have collided. However the
chances of their stars hitting are billions to one. These galaxies have
huge clouds of gas and dust. These structures could easily collide,and
add greatly to the compression force of gravity. Well these thoughts
come from knowing gas and dust clouds can be over 750 light-years
across. I can further think of emerging galaxies over time ending up
with two massive blackholes revolving around each other,and being more
dense than an average elliptical galaxy.(siamese twins). If it was two
spiral galaxies coming together I can visualize stars on there very edge
being left out of the pack. Bert