Scientists find a white dwarf with two faces (and they can’t really explain it)

Astronomers are baffled. Because on one side, the newly discovered star is made of hydrogen, while the other side is made of helium.

Meanwhile, many white dwarf stars have already been discovered in the universe. This means that researchers already know a lot about these “dead stars”. However, it turns out that they still have surprises waiting for us. Because for the first time, scientists have encountered a white dwarf with two markedly different faces.

white dwarfs
As you may already know, white dwarfs are the remnants of boiling stars that once resembled our Sun. As stars age, hydrogen fusion in the star’s core stops and it swells. Then a red giant is formed. When the star then explodes from its outer layers of gas and dust, the core contracts, leaving a white dwarf. The star has come to the end of his life. Our sun will also end up as a compact white dwarf in five billion years.

like
In a new study, researchers take a closer look at a newly discovered white dwarf. The star was used Zwicky Transit Facility (ZTF), a machine that scans the sky every night. Follow-up research revealed that the star rotates on its axis every 15 minutes.

two faces
So far nothing special. But subsequent observations using the W.M. Keck Observatory in Hawaii revealed something startling. The team used a spectrometer to analyze the light from the white dwarf. The data revealed the presence of hydrogen when one side of the star was visible (with no signs of helium), and only helium when the other side was oscillating. In short, the star appears to have two sides, one side made of hydrogen and the other side made of helium. “The surface of the star is therefore fundamentally different from one side to the other,” researcher Ilaria Kayazo said.

double faced
Because of the white dwarf’s dual nature, the star is called Janus, after the Roman god of beginnings and endings, who was also depicted with two faces. Researchers are still not sure of the exact cause. However, they did come up with some potential theories for the puzzling phenomenon.

From hydrogen to helium
“Some white dwarfs first have a hydrogen-dominated surface and then they get a helium-dominated surface,” Kaizo explains. “Maybe we caught a white dwarf in the act.”

correct
When a white dwarf sees the light of day, heavier elements “sink” into the core. The lighter elements — hydrogen being the lightest — then float to the surface. Over time, as the white dwarf continues to cool, all of the elements mix together. However, in some cases, the hydrogen inside becomes so dilute that the helium takes over. Janus may embody this transitional stage. Although in this case the question arises as to why the transition occurs in an incoherent manner, with one side developing earlier than the other.

magnetic field
Researchers believe it may have something to do with the white dwarf’s magnetic field. “They are usually unequal or stronger on one side,” says Caiazzo. They can even prevent materials from mixing. So if the magnetic field is stronger on one side, fewer elements get mixed in here, resulting in more hydrogen.” Another option is that the magnetic field changes the pressure and density of atmospheric gases. “Magnetic fields can lead to lower gas pressures in the atmosphere,” explains co-author James Fuller. “Where they are strongest, a hydrogen ocean can then form.”

More white dwarfs
However, for now, speculation remains. “We don’t know which of these theories is correct, but we can’t think of any other way to explain the asymmetric aspects without magnetic fields,” says Fuller. To help solve the mystery, the team hopes to find more Janus-like white dwarfs using ZTF. And they are absolutely sure of that. “ZTF is very good at detecting foreign objects,” Caiazzo says. “And with the help of the Vera C. Rubin Observatory in Chile, which is still under construction, it will soon be easier to detect white variable dwarfs.”

This creates hope. Because maybe in a few years we will learn more about the dual nature of Janus, who is still the cosmic oddity guy for the time being.