Recently, astronomers made a discovery that upended everything we thought we knew about white dwarfs by finding a very unusual specimen: a white dwarf that appears to have one side made up of hydrogen and the other side made up of helium. What is his name? Well, it's obvious.
The Discovery of Janus
This two-faced white dwarf has been dubbed Janus, after the two-faced Roman deity. The scientists examined Janus using data from two observatories, Caltech's Palomar in San Diego and the WM Keck Observatory on Maunakea, Hawaii.
Imagine a celestial body that rotates on its axis every 15 minutes, allowing researchers to view both sides of it. A celestial body with two completely different faces. On one side, a brilliant surface of hydrogen. On the other, a helium surface, which appears as if bubbles of gas are rising from its depth.
Ilaria Caiazzo of Caltech, an astrophysicist from Piedmont and principal investigator of the study, described the surprising nature of Janus: “The surface of the white dwarf changes completely from one side to the other. When I show people observations, they are blown away.”
An unexpected phenomenon
The "double-faced" nature of this white dwarf could be due to the fact that Janus is going through a particular evolutionary stage.
Caiazzo itself explains: “Not all, but some white dwarfs transition from a hydrogen to a helium dominance on their surfaces. We may have intercepted a white dwarf during this transition.”
Why this evolution should manifest itself so clearly is still a mystery. Scientists believe it could be related to the magnetic fields of the white dwarf. These fields could be asymmetrical or could alter the pressure of gases in its atmosphere.
"Two-faced" White Dwarf: looking for answers
To better understand this remarkable find, the researchers plan to look for other Janus-like objects as part of the observation.
The research, which has the potential to rewrite textbooks on stellar evolution, was published in the prestigious journal Nature (I link it to you here).