Starlight - Main Sequence - O - B - A - F - G - K - M - Luminosity Classes - Spectral Class Codes
K Main Sequence stars are smaller and cooler than the Sun. They fuse hydrogen very slowly. Their fuel will last for hundreds of billions of years. There has not been sufficient time for K class stars to reach their end points. Eventually they will become Red Giants, and finally they will lose their atmospheres as Planetary Nebulae and become White Dwarfs. Their surface temperature is around 3500° K. Alpha Centauri B is a K1V star.
