A huge, very hot, very luminous, blue post-main-sequence star; spectral type O or B. These rare, extremely hot stars burn helium. and are very rare and very bright. Blue giants are at least 18 Sol or more in mass. Examples include Rigel and Regulus.
Hot Luminous Stars - Text by Chris Clowes Stars occupying the top left corner of the Hertzsprung-Russell Diagram. They are among the most spectacular inhabitants of the galaxy. They evolve quickly and encompass a range of stellar types during their lifetimes. They include Type O, Type Of, Ofpe/WN9, Wolf-Rayet, WNL, LBV, B[e] stars.