[doc30]

AFAIK, it would be the same as our galaxy encountering a galaxy of visible matter of equal mass: they would pass through each other with virtually no star/star collisions (galaxies are mostly empty space). OTOH, there would be profound gravitational interactions -- many stars, clusters, etc. would be ripped out of their usual orbits and get flung all over the place. Lots of disruption possible from gravitational interactions.

Could be perilous for some planets, while others may go unscathed.

I agree with you completely on the isuee of the effects on planets and starts duting such a collision. What vexes me is the structure of dark matter. Does it form some type of "proton" or "electron"? Is it homogeneously distributed or is there some kind of structure behind it? Does it aggregate to form large masses the way normal matter forms planets and stars, or even simple dust grains? With all that mass, can dark matter form black holes? Are there different types of dark matter? Evidence of its existence, like this in the NASA report, is interesting, but it breeds a whole host of additional questions.

[longshadow]

What vexes me is the structure of dark matter. Does it form some type of "proton" or "electron"? Is it homogeneously distributed or is there some kind of structure behind it? Does it aggregate to form large masses the way normal matter forms planets and stars, or even simple dust grains? With all that mass, can dark matter form black holes? Are there different types of dark matter? Evidence of its existence, like this in the NASA report, is interesting, but it breeds a whole host of additional questions.

.... most of which cannot be answered until they come up with some idea of what the "dark" matter is made up of, which is probably a job for the particle physicists.

Physicist; do you have any info on lines of research trying to determine what the dark matter is? What do they know it is is NOT made out of?