How can dwarfs stars be so bright?
They are not
Stars are classified by the Morgan Keenan system by the letters O,B,A,F,G,K and M. O being the brightest and M having the most fainted light. The stars being classified as K and M are also divided into 2 groups, "Giants" and "Dwarfs". The giants are the ones being brighter then our sun and the dwarfs emit less light than our sun. Otherwise dwarfs are emiting their light the same way other stars do, by fusion of different elements.