The Goldilocks Zone. The above image is a great illustration of the relative size of the habitable zone around different types of star, with stars like our Sun at the bottom.
Even very dim M class dwarf stars (pictured top) could harbour planets with liquid water – the planets would just need to be situated much closer in. These stars can have very active magnetic fields however, frequently throwing harmful radiation out towards any orbiting planets. M class stars are also extremely stable, some destined to burn for over 100 billions years, much longer than our Sun which has around 4 billion years of fuel left.
In the middle we see the K class dwarf stars. These will also out live our Sun (by a factor of 4), have nice wide zones of habitation, and much less magnetic activity than the M class stars. Potentially these K class stars are the ideal incubators for the slow evolution of life, and there’s plenty of them. Nearly 13% of stars in our galaxy are K class red dwarfs. That’s approximately 26 billion in our galaxy alone!