However, it is likely that every rocky planet is infested with microbial life whether there is a sun or not, and that would include all rocky planets in the galaxy and all other galaxies. The trick is to realize that life doesn't need air; maybe we do, but not all life needs air or water. Think about it, though, oxygen powers our cars, heats our homes, and provides energy for us and our neural systems. High energy, about the highest energy system there is until the nuclear stage. Microbes living in rocks don't have that kind of energy available, so don't have the extra energy for mental processes.
Conclusion: Alien life, yes; aliens, no.