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B. O'Gorman, G.J. Mathews, I.-S. Suh, F. Weber ()
Recently, some puzzling features have emerged from the accumulated radii and masses of white dwarfs based upon Hipparchos parallaxes. In particular, some stars have radii much smaller than expected based upon their observed masses and standard models for white-dwarf structure. It has been proposed that those white dwarfs may contain an iron core. In this talk we argue that such iron cores are unlikely. We suggest that a plausible alternative may be a transition to strange quark matter within the white-dwarf core. We present revised calculations of the white-dwarf mass-radius relation based upon a well-constrained strange quark-matter equation of state. We argue that the data exhibit several features consistent with this hypothesis. We suggest that there is marginal evidence for a bimodality in white-dwarf populations one of which may contain strange-matter cores.