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A wonderful discovery that left astronomers scratching their heads. A white dwarf star with two distinct faceseach of which consists of different elements.
This lonely star, nicknamed “Janus,” after the two-faced Roman god, is located more than 1,000 light-years away in the constellation of Cygnus. The researchers, led by Dr. Ilaria Kayazu of the California Institute of Technology, made this startling discovery using the Zwicky Transit Observatory (ZTF), an observatory near San Diego, according to a report from the California Institute of Technology. guardian.
Janus: a star with unusual properties
Janus was singled out for its rapid changes in brightness, and further observations revealed that the star rotates on its axis every 15 minutes. What sets Janus apart is the stark difference between its two sides — one side is made up almost entirely of hydrogen, while the other side is made up mostly of helium.
If we look closely, both sides will appear bluish, but the helium side will have a patchy appearance like our sun, while the hydrogen side will look smoother.
“The surface of the white dwarf shifts completely from one side to the other,” said Dr. Ilaria Kayazu, an astrophysicist at the University of Michigan. California Institute of Technology said in the report. “When I show people the notes, they’re dumbfounded.”
What is a white dwarf?
White dwarfs are remnants of stars that were once similar to our sun.
As these stars age, they expand into red giants before shedding their outer material and shrinking into dense white dwarfs.
Inside the white dwarf, the heavier elements sink to the core, forming a layer of helium beneath a thin layer of hydrogen. As the star cools, the helium layer sheds, causing the mixing and gradual disappearance of the outer hydrogen layer.
But why is Janus so different?
The initial detection was made using the Zwicky Transient Facility (ZTF), a powerful sky survey instrument based at Caltech’s Palomar Observatory. The lead researcher, Dr. Ilaria Caiazzo, has been searching for highly magnetized white dwarfs like ZTF J1901+1458, which her team had previously found using ZTF.
The perplexing question remains: Why does this lonely white dwarf in space have completely different faces? While the team is baffled, they suggest some possible explanations. One theory is that Janus may be going through a rare phase of white dwarf evolution, according to California Institute of Technology a report.
According to Caiazzo, not all, but some white dwarfs are going through a transition from being hydrogen-dominated to being helium-dominated on their surface. The team wonders if Janus could be one of the white dwarfs caught up in this intriguing metamorphosis.
After white dwarfs form, their material separates, with heavier elements sinking into the core and lighter elements, such as hydrogen, floating to the surface. As it cools, the materials are expected to mix and, in some cases, dilute the hydrogen, making the helium more diffuse. Janus may represent this transitional stage, But the mystery remains: Why does this shift occur in a disjointed fashion, with one side evolving before the other?
Magnetic fields may hold the key to this mystery
Scientists suggest that magnetic fields may hold the key to this puzzle. Magnetic fields around celestial bodies often exhibit asymmetry, and are stronger on one side. These fields can hinder the mixing of materials, which means that if one side of Janus has a stronger magnetic field, it will mix less and hold more hydrogen.
Another theory proposed by the team also involves magnetic fields, but in this scenario, the fields alter the pressure and density of atmospheric gases. Magnetic fields can depressurize the gas, creating a hydrogen “ocean” where the magnetic fields are strongest.
To solve the mystery, the team plans to search for more Janus-like white dwarfs using ZTF’s sky survey, which excels at spotting unusual objects. Future surveys, such as those from the Vera C. Rubin Observatory in Chile, are expected to make finding variable white dwarfs easier, according to the report from California Institute of Technology.
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