A red dwarf star is a small and cool star on the main sequence of the Hertzsprung-Russell diagram. These stars have a mass between about 0.08 and 0.6 times that of the Sun, making them the least massive type of star. They are known for their long lifespans, often lasting tens to hundreds of billions of years, which is much longer than larger stars like yellow dwarfs. Red dwarfs are typically dim and emit most of their energy in the infrared spectrum. Due to their low brightness, they are often difficult to observe from Earth. Many of the stars in our galaxy, including some in the Proxima Centauri system, are red dwarfs, making them a common type of star in the universe.