Hertzsprung-Russel graph is a 2-dimensional graph, plotting star’s luminosity against temperature they emit.
White dwarfs are the star exhibiting high temperatures and low luminosities. These stars are extremely dense and mass comparable to that of the sun.
The main cause of low luminosities in the absence of fusion reaction inside the core of the star. Faint luminosity is provided by the thermal energy of the star. They are considered to be in the final stage of evolution having masses in the range of 10 solar mass (hence not enough to form a star)
