Janus: Why this dying star has two faces but one core
Scientists have affectionately dubbed it 'Janus' due to its extraordinary characteristic of having hydrogen on one side and helium on the other
July 22, 2023
Figuratively speaking, some individuals can be described as two-faced, displaying different personas.
However, in ancient Roman mythology, the god Janus was quite literally depicted with two faces—one facing forward and the other backward, symbolising transitions and duality.
Surprisingly, in the cosmos, scientists have discovered a star that is two-faced as well.
This unique celestial object is a white dwarf star, which is a dense and hot stellar remnant.
Scientists have affectionately dubbed it "Janus" due to its extraordinary characteristic of having hydrogen on one side and helium on the other.
This peculiar composition sets it apart from the usual stellar patterns observed in the cosmos and adds a fascinating aspect to our understanding of celestial bodies.
"Janus is the Roman god with two faces, so we thought it was very appropriate. Moreover, Janus is the god of transition, and the white dwarf might be currently transitioning from having an atmosphere made of hydrogen to one made of helium," said Ilaria Caiazzo, a Caltech postdoctoral fellow in astrophysics and lead author of the study published this week in the journal Nature.
Situated within our Milky Way galaxy, the star resides approximately 1,300 light years away from Earth, positioned in the direction of the Cygnus constellation.
To put it in perspective, a light year signifies the vast distance light travels in the span of a year, covering an astonishing 5.9 trillion miles (9.5 trillion km).
Dubbed "Janus," this particular white dwarf star boasts a relatively substantial mass, being about 20% larger than our sun, all compacted into an object with a diameter merely half that of Earth.
What's even more remarkable is its rapid rotation on its axis, completing a full rotation every 15 minutes.
This rotational speed is significantly faster compared to typical white dwarf stars, which usually take several hours to a few days to complete one rotation.
Janus's unique features make it an intriguing subject of study in the realm of celestial phenomena.
"White dwarfs form at the very end of a star's life. About 97% of all stars are destined to become white dwarfs when they die," Caiazzo said.
"Our sun, for example, is currently burning hydrogen into helium in its core. When the hydrogen in the core is depleted, the sun will start burning helium into carbon and oxygen. When the helium also is gone from the center, the sun will eject its outer layers into space in an event called a planetary nebula and the core will slowly contract and become a white dwarf," Caiazzo added.
