Dwarf stars are small and relatively cool stars that fall into several categories, including red dwarfs, white dwarfs, and brown dwarfs. They are typically less massive than main-sequence stars like our Sun and have lower luminosity. Red dwarfs are the most common type, making up about 70% of the stars in the universe. White dwarfs are the remnants of stars that have exhausted their nuclear fuel and shed their outer layers. They are very dense and hot but gradually cool over time. Brown dwarfs are substellar objects that are not massive enough to sustain hydrogen fusion, placing them between the largest planets and the smallest stars.