Introducing Janus, the Exotic ‘Two-Faced’ White Dwarf Star

WASHINGTON—Some people are two-faced, figuratively speaking of course. The ancient Roman god Janus was two-faced, literally—with one looking forward and another backward, representing transitions and duality. But a two-faced star? Yes, indeed.
Scientists have observed a white dwarf star—a hot stellar remnant that is among the densest objects in the cosmos— that they have nicknamed Janus owing to the fact it has the peculiar distinction of being composed of hydrogen on one side and helium on the other.
“Janus is the Roman god with two faces, so we thought it was very appropriate. Moreover, Janus is the god of transition, and the white dwarf might be currently transitioning from having an atmosphere made of hydrogen to one made of helium,” said Ilaria Caiazzo, a Caltech postdoctoral fellow in astrophysics and lead author of the study published this week in the journal Nature….