All of these projections depend on a fundamental assumption: that the two galactic cores actually hit. If it's even a near miss - say, each galactic core passes through one of the spiral arms of the other galaxy, which is an incredibly near miss on this scale, roughly equivalent to a sniper hitting the wrong eye of a target from 10,000 feet - then the effects are going to be much less spectacular.
The most devastating part of such a near miss would be the increase in the density of the interstellar medium, though it would have far less of an effect than a core collision. Background radiation would rise, possibly be an order of magnitude - bad news for radio astronomy, since it give you much more noise to filter, but not particularly threatening to anyone on a planet with a nice thick atmosphere and a healthy magnetic field. Possibly one star per hundred thousand would be involved in a stellar collision event, with terminal effects on any stellar system involved, but stellar collisions are very rare events. Most people don't realize
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Re: ...Or not.polaris93February 3 2010, 04:34:04 UTC
This video presents a simulation of a galaxy-galaxy collision, in this case, of the Milky Way with the Andromeda Galaxy. Simulations always depend on the paradigms and the initiating values of the variables used in them. This video shows one possible simulation among many. You're right about collisions between stars being very, very rare. They happen almost exclusively among stars orbiting close to their galaxy's black hole, because the high angular velocity and dense crowding of such stars makes collisions inevitable over relatively short periods of time. In collisions between galaxies, since most stars in those galaxies are far out from the supermassive black holes at the centers of the galaxies, they are unlikely to collide at all with stars in the other galaxy. It is the collision of huge amounts of gas and dust at very high velocities and the interaction of the electromagnetic fields of the two galaxies that releases titanic amounts of energy. For example, in ngc 3256 (... )
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The most devastating part of such a near miss would be the increase in the density of the interstellar medium, though it would have far less of an effect than a core collision. Background radiation would rise, possibly be an order of magnitude - bad news for radio astronomy, since it give you much more noise to filter, but not particularly threatening to anyone on a planet with a nice thick atmosphere and a healthy magnetic field. Possibly one star per hundred thousand would be involved in a stellar collision event, with terminal effects on any stellar system involved, but stellar collisions are very rare events. Most people don't realize ( ... )
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