The Blue Dwarf is an interesting concept I've recently discovered, see my little write up about it below.

The smaller a star gets the less energy it needs to stop its own collapse, as a result M class stars burn their hydrogen fuel slowly. Compound this with the fact that red dwarfs are fully conductive, meaning that the hydrogen fuel within the star can completely circulate and all possible fuel can be used. This means that these stars have really long lifetimes of hundreds of trillions of years.

However, when they do run out of hydrogen fuel they will start to leave the main sequence much like every other star. As they do so they will start to burn hotter and brighter, some even becoming as bright as the sun is today. So trillions of years from now a new era of the universe will begin, the era of the blue dwarf. The blue dwarf stage of these stars has been estimated to last hundreds of billions of years, providing light and energy for a tremendous amount of time. Time far longer than the current age of the universe.

So cold and frozen worlds that lie outside of their star's habitable zone will in time find themselves enveloped in heat and light, and may provide another stage for the spectacle of life. Imagine life and civilizations being born on planets that are not billions of years old, but have been awakened after hundreds of trillions of years of frozen slumber.

Additional link to blog post, not by me.

[beyondearthlyskies.blogspot.com]