Star Upsilon Andromedae D

Red dwarfs are small, cool stars with surface temperatures of about 2,000–3,800 K, much cooler than the Sun. They usually have 8–50% of the Sun’s mass and shine very faintly, sometimes at just a tiny fraction of the Sun’s brightness. Classified mainly as spectral type M, they are the most common stars in the Milky Way, making up roughly 70–75% of its stellar population.

They fuse hydrogen slowly through the proton–proton chain and are fully convective, which allows them to use their fuel very efficiently. As a result, red dwarfs can live for tens of billions to trillions of years—far longer than the Sun. Many exoplanets orbit red dwarfs, including some in close habitable zones, though strong stellar activity can affect planetary environments.