Strange white dwarf discovered, split by hydrogen and helium gas

In billions of years, the moment our sun burns out of its own fuel and swells up to become a red giant before 'exploding' to form a planetary nebula, all that What remains at its center will be a solid core known as a white dwarf.

This is in fact the common fate of most of the stars located in our galaxy. Recently, however, international astronomers have suddenly discovered an extremely unusual example of a white dwarf: A white dwarf is roughly bisected into two symmetrical halves, with one side consisting of all the stars. hydrogen molecules and helium on the other.

Due to its strange appearance, this white dwarf has been nicknamed Janus, after the Roman god with two faces, and has been studied using data from the Zwicky Transient system. Facility at Caltech Palomar Observatory (San Diego) and WM Keck Observatory (Hawaii). Every 15 minutes, Janus completes one rotation on its own axis. Such an extremely fast rotation allows scientists to relatively closely observe the two sides of the star.

'The surface of this white dwarf changes completely from side to side,' study leader Ilaria Caiazzo of Caltech said in a statement. 'The results of the observations surprised us all'.

The scientists also found some chemical identifiers of hydrogen on the helium-free half and the hydrogen-free helium on the other. The team believes this highly unusual phenomenon could be because Janus is going through a special evolutionary phase, rare for typical white dwarfs known to man.

However, the question of why this evolution is presented in such a 'half-hearted' way needs further explanation. The researchers suggest that this is most likely related to the white dwarf's magnetic field, which may be asymmetrical or possibly change the gas pressure in the atmosphere.

'The magnetic fields around cosmic bodies tend to be asymmetrical or stronger in one direction,' Caiazzo said. 'Magnetic fields can prevent the mixing of matter. So if the magnetic field is stronger on one side, that side will be less mixed and there will be more hydrogen."

To better understand this strange find, the researchers aim to look for more Janus-like objects as part of a survey of the sky being carried out by the Zwicky Transient Facility system.

David Pac

Update 27 July 2023