Astronomers have been left stumped and riddled with questions after discovering that at least one white dwarf exhibits a two-faced nature, with one side composed of hydrogen and the other made up of helium.
Lead researcher Ilaria Caiazzo, a postdoctoral scholar at Caltech, describes the white dwarf's transformation from one side to the other as a complete surface change.
"The surface of the white dwarf completely changes from one side to the other," said Caiazzo. "When I show the observations to people, they are blown away."
The unique white dwarf, named Janus after the two-faced Roman god, was initially detected by the Zwicky Transient Facility.
The celestial body's rapid changes in brightness caught Caiazzo's attention, which then prompted a further investigation using the CHIMERA instrument at Caltech's Palomar Observatory and the HiPERCAM on the Gran Telescopio Canarias in Spain's Canary Islands. The results confirmed that Janus rotates on its axis every 15 minutes.
Subsequent observations made with the W. M. Keck Observatory in Hawaiʻi revealed the dramatic duality of the white dwarf. The team used a spectrometer to analyze the light and found that when one side of Janus was in view, it consisted predominantly of hydrogen, with no signs of helium, whereas the other side showed only helium.
Researchers have put forward several theories to explain this unusual phenomenon. One theory suggests Janus may be undergoing a rare phase of white dwarf evolution, where some white dwarfs transition from being hydrogen- to helium-dominated on their surface.
As white dwarfs cool over time, heavier elements sink to their cores and lighter elements, such as hydrogen, rise to the top. However, the question remains as to why this transition is happening in such an asymmetrical manner, with one side evolving before the other.
The team also speculates magnetic fields play a crucial role in Janus' unique characteristic.
"Magnetic fields can prevent the mixing of materials. So, if the magnetic field is stronger on one side, then that side would have less mixing and thus more hydrogen," explained Caiazzo.
Another theory proposes that magnetic fields may alter the pressure and density of the atmospheric gases, leading to the observed differences.
Further research and observations are needed to unravel the mysteries behind Janus and determine the factors responsible for its distinct faces. The discovery opens up new avenues for understanding the complex evolution of white dwarfs and the role that magnetic fields play in shaping celestial objects.
The findings of the study were published in the journal Nature.