Could there be life in the galaxies nearest to the Milky Way?
Is there any reason that there may not be, or might not have been, inhabited planets in the galaxies that are nearest to the Milky Way?
The galaxies that are nearest to the Milky Way are mostly small galaxies that aren't very bright. Some of them (though not all) have low rates of star formation, and many are in the process of being torn apart by gravitational interaction with the Milky Way.
Overall, these qualities aren't very favorable for the presence of Earth-like planets and life. Galaxies that aren't very bright also tend to have low metallicities (metallicity is a measure of the amount of elements heavier than hydrogen and helium in the galaxy; these elements are created in the cores of dying stars - in particular, hot bright stars - so bright galaxies with long histories of star formation are more likely to have high metallicity). These heavy elements are needed in order for rocky planets like the Earth to form. In addition, irregular galaxies being torn apart by the Milky Way might not be favorable places for life to form because of the complicated orbits that the stars follow within the galaxy, which could potentially bring the stars close to dangerous objects. Spiral galaxies, where the stars go in well-defined orbits, are more stable and safer for the long-term prospects of life.
This is not to say that there couldn't be life in these galaxies. However, the most favorable galaxies for life are probably those like the Milky Way - big, bright spiral galaxies. The Andromeda Galaxy is the only other galaxy within our Local Group that is similar to the Milky Way - basically, the Local Group consists of the Milky Way and Andromeda plus a bunch of small "satellite galaxies" of each. If I were looking for intelligent life outside the Milky Way, I would probably focus on Andromeda rather than the small satellite galaxies that are nearer to us.
For more information about the sorts of environments within a galaxy that might be hospitable to life, have a look at the article in the October 2001 issue of Scientific American entitled "Refuges for Life in a Hostile Universe" (by Guillermo Gonzalez, Donald Brownlee and Peter D. Ward). I could not find this story on the Scientific American website but I did find a PDF copy from another source.
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