Fate of Galaxies: Will Stars be Pulled into Black Holes?

[pforeman]

In the far distant future, will all of the stars in a galaxy be pulled into one giant black hole in the center?
Are the arms of spiral galaxies like our milky way spiralling in or flying out?
Thanks
Paul

 

[Chronos]

That is still being debated. I seriously doubt 'all' stars will be absorbed by supermassive black holes, which seriously complicates any theory the universe will eventually achieve a state of perfect thermodynamic equilibrium.

 

[Chalnoth]

In the far distant future, will all of the stars in a galaxy be pulled into one giant black hole in the center?
Are the arms of spiral galaxies like our milky way spiralling in or flying out?
Thanks
Paul

For the most part, the orbits of stars in our galaxy are extremely stable. For objects close to the black hole, there is some gravitational radiation that causes the objects to lose orbital energy. But the magnitude of this radiation is extremely dependent upon distance, and is pretty negligible for objects even a short (in astrophysical terms) distance away.

Every once in a great while, there will be a close interaction between stars which transfers enough momentum to one star to kick it out of the galaxy. The galaxy loses one star, but the remaining stars have less orbital energy between them and are, after that interaction, on average a bit closer to the orbiting black hole. After many such interactions, more stars are liable to have fallen into the central black hole.

At the same time, matter within our galaxy is (occasionally) forming smaller stellar black holes which very slowly radiate away to nothing.

On extremely long time scales, matter itself is likely to decay through a process known as proton decay.

All of these processes are incredibly slow, and I couldn't tell you which will win out. But Wikipedia has a nice article on the subject:
http://en.wikipedia.org/wiki/Future_of_an_expanding_universe