The classes are O, B, A, F, G, K, and M, with O-type stars being the hottest, densest hypergiants and K and M stars being the coolest red dwarfs and supergiants. Some classifications contain even cooler-temperature objects that might be brown dwarfs (objects too hot to be planets and too cool to be stars) or even rogue planets. They are labeled L, T, and Y, and some of them are known to be cooler than planets.
