Shocked, scientists discovered an unprecedented star that changes its face

Astronomers have discovered a star with a face of Janus, the properties of which surprised even scientists, – the online edition of the Guardian newspaper reported on Wednesday.

According to a study published in the journal Nature, one side of the white dwarf appears to be composed almost entirely of hydrogen and the other helium. No single star with such a spontaneously forming duality has ever been discovered before.

As explained by Ilaria Kaizo, an astrophysicist at Caltech, who led the research, the two sides of the white dwarf’s surface are very different. As he said, even his colleagues were surprised by this.

Discovered more than a thousand light-years away in the constellation Cygnus, Janus is named after the two-faced Roman god, and its scientific name is ZTF J1901+1458.

Janus was first detected by the Zwicky Transient Facility (ZTF) telescope at Caltech’s Palomar Observatory.

Caiazzo was searching for white dwarfs, and one candidate stood out due to the rapid changes in light. It turns out that Janus rotates on its axis every 15 minutes. Spectral analyzes showed that one side contained only hydrogen and the other almost exclusively helium.

Close up, researchers say, both sides of the star will be bluish in color and similar brightness, but the helium side will appear mottled and the hydrogen side will appear smooth.

One explanation from astronomers is that Janus may be going through a rare phase transition that occurs during the evolution of white dwarfs.

White dwarfs represent the last stage in the evolution of stars, and they usually shrink to about the size of the Earth, while their mass is almost the same as that of the Sun, so their density is very high. White dwarfs have extremely high surface temperatures, which is why they emit bright white light.

As a result of the star’s intense gravitational field, heavier elements sink into the core, while lighter elements float, the atmosphere composed of two layers of a thin layer of hydrogen on top of a layer of helium. When the star’s temperature drops below 30,000 degrees Celsius, bubbles form in the thick helium layer, and mix with the hydrogen layer, which softens and disappears from view.

According to Caiazzo’s interpretation, there are white dwarfs whose surface hydrogen is replaced by helium, and it is possible that this transition was observed in the case of Janus.
According to the scientist’s theory, if this is the case, perhaps the asymmetric magnetic field can cause the observed phenomenon: because if the magnetic field is stronger on one side, it can limit bubble formation in the helium layer, while bubble formation occurs on the other side and the hydrogen layer disappears.