Starlight - Main Sequence - O - B - A - F - G - K - M - Luminosity Classes - Spectral Class Codes
Main sequence M Stars, Red Dwarfs, are the smallest* main sequence stars. M stars fuse hydrogen very slowly. Their surface temperature is around 2500° K. Much of their radiation output lies in the infrared region. Their fuel will last for a trillion years. Proxima Centauri, the nearest star to the Sun is a M5V star. M stars are the most common type of star in the Milky Way galaxy. There are more Main Sequence M type stars than all other spectral types combined.
Once they have exhausted their fuel, they will simply cool to large planet like cinders. No such bodies have been found. There has not been enough time since the universe began for them to form.
*Bodies smaller than M8 stars cannot become stars. They do not develop enough pressure and temperature
to sustain fusion. They are classified as Brown Dwarfs and Gas Giant Planets.