Habitability of red dwarf systems
The theorized habitability of red dwarf systems is determined by factors including tidal effects, flaring, and variability. Modern evidence suggests that planets in red dwarf systems are unlikely to be habitable, due to high probability of tidal locking, likely lack of atmospheres, and the high stellar variation many such planets would experience.
Source: Wikipedia — Habitability of red dwarf systems (CC BY-SA 4.0)