Two-Faced Star Discovered; White Dwarf Features Hydrogen on One Side, Helium on the Other

A white dwarf baffled astronomers after discovering it was a two-faced star. It has a bizarre appearance due to its two contrasting faces.

Two-Face Star Discovered

Dr. Ilaria Caiazzo, an astrophysicist at Caltech, who led the work, said the surface of the white dwarf changes from one side to the other, which blew them awayOnene of its sides is made up of helium, while the other half is made up of hydrogen, ScienceDaily reported.

A particular star stood out in Caiazzo's search for white dwarfs because of its quick brightness variations. Additional observations showed that Janus rotated once every 15 minutes. One side of the object was almost totally composed of hydrogen, and the other side was almost entirely composed of helium, according to spectrometry studies, which reveal the chemical fingerprints of a star.

Both sides of the star would appear smooth and bluish if observed up close, but the helium side would have a grainy, patchwork appearance akin to our sun, while the hydrogen side would appear more even in color and brightness. Since the star's shell is covered with swirling gas, it is challenging to understand why it has two faces.

Anything is difficult to separate, according to Caiazzo. One theory is that Janus might be going through a rare transition that is supposed to happen during the evolution of white dwarfs.

The seething remains of stars that formerly resembled our sun are white dwarfs. Red giants form as the stars get older. The core eventually shrinks into a dense, blazing, scorching white dwarf that is about the size of Earth and has a mass similar to that of our sun once the fluffy outer material is eventually blown away.

A two-tiered atmosphere of helium with a thin layer of hydrogen (the lightest element) on top is created by the star's strong gravitational field, which causes heavier elements to sink to the star's core and lighter ones to float.

The thicker helium layer starts to bubble when the star cools to below 30,000C (54,032F), which causes the outer hydrogen layer to mix with it, get diluted, and eventually vanish from view.

Some white dwarfs, but not all, change their surface composition from hydrogen to helium predominance, according to Caiazzo. One of these white dwarfs may have been captured in the act by us.

If so, the researchers think that an unbalanced magnetic field may be to blame for the uneven transition. According to Caiazzo, if the magnetic field is stronger on one side, it might restrict convection or bubbling in the helium layer. On the other hand, convection might be taking control, losing the hydrogen layer.

The study was published in the journal Nature.

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What Is a White Dwarf?

White dwarfs are stars like the Sun after using up all of their nuclear fuel. This kind of star expels most of its outer material as it nears the conclusion of its nuclear burning cycle, forming a planetary nebula, per NASA.

The star's scorching core is all that is left. When this core reaches a temperature of more than 100,000 Kelvin, it turns into a very hot white dwarf. Over the course of the following billion years or so, the white dwarf cools down unless it is accreting material from a nearby star (see Cataclysmic Variables).

There are a lot of nearby young white dwarfs that have been identified as soft or lower-energy X-ray sources. Recent advances in soft X-ray and extreme ultraviolet observations have made them potent tools for studying the makeup and structure of these stars' thin atmospheres.