Impressions of the author of the two-faced star Janus
K. Miller, Caltech/IPAC
Astronomers have discovered a double-faced star with each face having a different composition. The white dwarf, named Janus after the Roman god of gateways and change, is the first star of its kind to be discovered.
Jeremy Hale Doctors and colleagues at the University of British Columbia in Canada discovered Janus using the Twicky Transient Facility in California, and then used several other telescopes to make further observations. Observations have shown that one side of the star is composed entirely of hydrogen and the other side is composed entirely of helium. From Earth she is more than 1,300 light years away and rotates about once every 15 minutes.
We know that the entire surface of some white dwarfs can change from helium to hydrogen and back to helium again, but we have never seen a white dwarf in the midst of this change with certainty. The mechanism behind it still remains obscure.
“This seems to have something to do with the magnetic field being slightly stronger on one side of the star than the other, but the data themselves show no evidence of a very strong magnetic field,” Hale says. “I mean, we still don’t fully understand what’s going on.”
In the presence of such a magnetic field, convection, or internal stirring, of the star will be suppressed only on the side where the magnetic field exists. stronger. White dwarfs are mostly made of hydrogen and helium, so the lighter hydrogen floats naturally to the surface on the side without convection, while the more abundant helium bubbles to the top on the other side.
“At lunar distance, you can clearly see these convective patches, with one half appearing about 15% brighter than the other,” Hale says. “Its temperature is about five times that of the sun, so it would be incredibly bright to the eye and uncomfortable to look at.”
The fact that we have only found one of these stars despite exploring much of the universe means that these objects are probably relatively rare. It was also an incredible coincidence that we were able to identify it. The axis of rotation just happens to be perpendicular to the boundary between the helium and hydrogen planes, and we just happen to be facing the star.
With this good fortune, the researchers hope to get more detailed data on Janus to understand how exactly its internal dynamics work. This star may hold the key to explaining this strange stage in the evolution of white dwarfs.
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