The stars in order from smallest to largest are the brown dwarfs, red dwarfs, white dwarfs, main sequence stars, giant stars, and supergiants. Brown dwarfs are the smallest and coolest of all star types. They are too small to sustain nuclear fusion reactions in their cores and instead cool and fade over time. Red dwarf stars are slightly larger and hotter than brown dwarfs but still much cooler than our Sun. White dwarf stars are even hotter than red dwarf stars but have very little mass left after they exhaust their fuel supply and enter retirement. Main sequence stars like our Sun make up the majority of known star types. These middle-of-the-road objects fall somewhere between red dwarves and giantstars in terms of size and luminosity. Giantstars are much more massive than main sequence stars but have used up most of their hydrogen fuel supply so they start to cool down as they age. Supergiantsare the largest type of star knownâ€”they can be hundreds or even thousands of times more massive than our Sun!