The third known triple white dwarf: The close double white dwarf SDSS J125733.63+542850.5 hosts a white dwarf tertiary
Camila Aros-Bunster, Matthias R. Schreiber, Odette Toloza, Mercedes S. Hernandez, Diogo Belloni, Kareem El-Badry, Zach Vanderbosch, Felipe Lagos-Vilches, Boris T. Gänsicke and Detlev Koester