Two-faced star exposed in first for astronomy

An unusual white dwarf star is made of hydrogen on one side and helium on the other. In a first for white dwarfs, the burnt-our cores of dead stars, astronomers from institutions including the California Institute of Technology (Caltech) and the University of Warwick have discovered that at least one member of this cosmic family is two faced. The findings, that one side of the white dwarf is composed of hydrogen, while the other is made up of helium, were published today in Nature. White dwarfs are the scalding remains of stars that were once like our sun. As the stars age, they puff up into red giants, but eventually their outer fluffy material is blown away and their cores contract into dense, fiery-hot white dwarfs. Our sun will evolve into a white dwarf in about 5 billion years. The newfound white dwarf, nicknamed Janus after the two-faced Roman god of transition, was initially discovered by the Zwicky Transient Facility (ZTF), an instrument that scans the skies every night from Caltech's Palomar Observatory near San Diego.