 They are estimated to be 11 to 12 billion years old.Because the far-future evolution of stars depends on physical questions which are poorly understood, such as the nature of dark matter and the possibility and rate of proton decay, it is not known precisely how long it will take white dwarfs to cool to blackness.Barrow and Tipler estimate that it would take 1015 years for a white dwarf to cool to 5 K; however, if weakly interacting massive particles (WIMPs) exist, it is possible that interactions with these particles will keep some white dwarfs much warmer than this for approximately 1025 years.