When you hear the word “serpent” or “snake”, the symbol of the Ouroboros may come to mind—the serpent that devours its tail, embodying the idea of eternity and the cycle of life and death. If you are interested in chemistry, you may recall Kekulé and the daydream in which he saw a snake coiling around itself and eating its tail, which inspired him to propose the ring structure of the benzene molecule. If you are a pharmaceutical or medial specialist, you may think of the Bowl of Hygieia or the Rod of Asclepius, where the serpent symbolizes healing, wisdom, and the renewal of life. If you are fascinated by ancient Egyptian mythology, you may recall the image of Apep), the serpent that tries to swallow the Sun and spread chaos every night.
A recent image captured by the James Webb Space Telescope reflects this shape; yet, what mythology presents as a serpent in the underworld appears as a real scene in the sky.
A Story Born Millions of Years Ago
Millions of years ago, an enormous cloud of gas and dust moved through space. Over time, gravity began to pull its matter inward, causing it to contract gradually and become denser and hotter. As the cloud reached a critical mass, matter piled up at its center and its temperature intensified, eventually forming a new protostar.
As pressure and temperature increased, the core of the young star became hot enough to fuse hydrogen nuclei into helium at an enormous rate. At this early stage, nuclear fusion was confined to only the hydrogen in the core. The outer layers were cooler and under too little pressure to allow fusion to occur. Therefore, the star preserved a vast reservoir of hydrogen in its outer layers, a remnant of the cloud from which it was born.
Over time, the hydrogen in the core depleted, causing it to contract and grow even hotter; it began fusing helium into heavier elements such as carbon, nitrogen, and oxygen. These violent reactions amplified the star’s radiation and strengthened its stellar winds to the extent that they stripped away its outer layers: first, the hydrogen-rich outer layer, then the helium-rich layer beneath it.
When the outer layers burst into space, the star’s core became bare, revealing a Wolf–Rayet star: a naked core blazing furiously, exposing what had long been hidden in its depths.
The core of our star shines with spectra rich in carbon, while some of its Wolf–Rayet peers display spectra dominated by nitrogen or oxygen as an evidence that they have progressed along their evolutionary paths. Wolf–Rayet stars are rare in the Milky Way; only a small number of stars possess the enormous mass needed to reach this stage of their lives. Moreover, this phase lasts only a few thousand years.
Apep System
At the heart of the Apep System—named after the Egyptian myth of the Serpent of Chaos—lies a binary system consisting of a nitrogen-rich Wolf–Rayet star, as well as a carbon-rich star whose journey we have traced. These two stars orbit one another, completing a full cycle roughly every 190 years. When they get closer along their long elliptical path, their stellar winds collide violently, compressing matter and cooling it rapidly enough for dust grains to form. As they continue to rotate, this dust is released into space, forming a spiral. Each ring in the spiral represents a past moment in the stars’ orbit, ultimately forming a helix that resembles a serpent. The story does not end there, since there is a third star that orbits this pair from a greater distance. Although it does not take part in the formation of the dust, its gravity and stellar winds distort the outer layers of the dust, producing a more complex, dynamic, and distinctive form.
Webb’s New Image
With its powerful mid-infrared camera, the James Webb Space Telescope has revealed details that were previously invisible. The image reveals four distinct dust layers, each representing a ring in the recent history of the system. Together, these layers represent nearly seven centuries of activity, expanding outward in a remarkable sequence. Their spacing indicates that dust production intensifies whenever the Wolf–Rayet stars reach the closest point in their orbit. Webb’s data also revealed the dust’s temperature, composition, and structure, confirming that it consists mostly of amorphous carbon. In the end, Wolf–Rayet stars will explode as supernovae, throwing their contents into space. One of the stars might release a huge burst of gamma rays before transforming into a black hole.
References
doi.org/10.1093/mnras/stw619
doi.org/10.1093/mnras/stx1496
science.nasa.gov
Cover photo credits: NASA, ESA, CSA, STScI, Y. Han (Caltech), R. White (Macquarie University), A. Pagan (STScI), CC BY 4.0, via Wikimedia Commons