The concept of duplicity in individuals, though not a physical trait like the ancient Roman god Janus, finds an intriguing counterpart in the cosmos.
Astronomers have come across a white dwarf star, a compact and intensely dense celestial object, with an unusual identity – it has earned the moniker Janus due to its unique composition: hydrogen on one side and helium on the other.
Drawing a connection to the Roman god Janus, who symbolized transitions and duality with two faces, the researchers found it fitting to name this enigmatic star.
Ilaria Caiazzo, an astrophysics postdoctoral fellow at Caltech and the lead author of the study published in the journal Nature, remarked, “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.”
This Janus star is situated in the Cygnus constellation, about 1,300 light years away from our Earth within the vast expanse of the Milky Way galaxy.
For context, a light year corresponds to the distance light travels in one year, spanning an astonishing 5.9 trillion miles (9.5 trillion km).
Comparatively substantial for a white dwarf, Janus possesses a mass 20% larger than our sun, tightly packed into an object with a diameter merely half that of Earth.
Remarkably, it rotates on its axis every 15 minutes, an exceptionally fast rate considering that most stars of this type usually rotate every few hours to a few days.
Caiazzo provided insight into the formation of white dwarfs, stating, “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.
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.”
Fortunately, the sun’s transformation into a white dwarf is anticipated to occur in a distant 5 billion years from now.
The discovery of Janus was facilitated by the Zwicky Transient Facility, situated at Caltech’s Palomar Observatory near San Diego. Subsequent observations of the star were conducted using various ground-based telescopes.
Following the formation of a white dwarf, its heavier elements tend to sink to the core, while lighter elements, such as hydrogen and helium, float toward the surface.
During certain stages of the evolution of some white dwarfs, this layered structure is believed to be disrupted by intense mixing, causing the hydrogen and helium to blend together.
Janus appears to embody a white dwarf in the midst of this transitional blending process, with the curious peculiarity of featuring hydrogen on one side and helium on the other.
The researchers hypothesize that the star’s magnetic field might be responsible for this asymmetry.
If the magnetic field is stronger on one side than the other, as often seen in celestial objects, it could lead to a lopsided distribution of elements, resulting in one side being hydrogen-rich while the other side is helium-dominated.
Caiazzo expressed, “Many white dwarfs are expected to go through this transition, and we might have caught one in the act because of its magnetic field configuration.”
Janus is not alone in its extraordinary characteristics among white dwarf stars. Caiazzo, part of a research team, had previously reported on another unique white dwarf in 2021.
This particular star, with a diameter slightly larger than Earth’s moon, possessed the greatest mass and smallest size among all known white dwarfs.
Caiazzo concluded, “Every time we look at stars in different ways, we are bound to be surprised and even baffled sometimes. Stellar phenomenology is extremely rich, and no two stars are the same if looked at closely enough.”
The vast and intricate cosmos never fails to captivate, revealing wonders beyond our imagination.