A new kind of “cold star” has been identified by astronomers. It is the faint
Jupiter-sized companion of a white dwarf in a binary system called WZ Sagittae
about 160 light years away. David Ciardi of the University of Wyoming, Laramie,
says it is a “stellar cinder” of a kind never seen before. It formed when a
superdense white dwarf captured most of the mass of a companion star.
The object lost its stellar status when its mass fell below the fusion
threshold for hydrogen and its nuclear fires sputtered out. In a future issue of
The Astrophysical Journal, Ciardi’s group estimates its temperature at
1700 K, well below the 2600 K of the coldest known hydrogen-burning star, and
the 6000 K of the Sun.
