Webb Telescope Unveils Hidden Dust Shells of Triple Star System Apep

The James Webb Space Telescope (JWST) has achieved another remarkable first, detecting four distinct dust shells surrounding the enigmatic triple-star system known as Apep. This groundbreaking observation, made possible by Webb's mid-infrared camera, significantly surpasses earlier images which had only managed to capture a single shell. Experts liken the enhanced imaging capabilities of the Webb telescope to illuminating a previously darkened chamber, bringing hidden details into sharp focus and revolutionizing our understanding of this unique cosmic phenomenon.

Beyond its profound scientific implications, this new image of Apep stands out as one of Webb's most aesthetically captivating and visually impressive photographs to date, a high standard considering the telescope's already stunning portfolio. The final composition integrates several years' worth of data from the European Southern Observatory's Very Large Telescope (VLT) in Chile, complemented by the incredibly rich and detailed images acquired by Webb's Mid-Infrared Instrument (MIRI).

MIRI, which uniquely combines both a camera and a spectrograph, is the sole mid-infrared instrument aboard the Webb telescope. Astronomers and scientists leverage its capabilities to explore celestial bodies that are relatively cooler or exceptionally distant. In this particular instance, Apep represents an extraordinary triple-star system situated approximately 8,000 light-years from Earth, a relatively close proximity in the vast cosmic expanse. It resides within the constellation Norma.

The distinctive nature of Apep lies in its three gravitationally bound stars, two of which are classified as Wolf-Rayet stars. While these three stars appear as a single luminous point in Webb's image, their profound mutual influence and broader systemic impact are vividly showcased. Dr. Ryan White, a PhD student at Macquarie University in Australia, highlighted the system's unparalleled orbital period, stating that the next longest orbit for a dusty Wolf-Rayet binary extends to roughly 30 years, whereas most typically fall within a two to ten-year range.

Wolf-Rayet stars are inherently rare cosmic entities. Out of the hundreds of billions of stars inhabiting the Milky Way Galaxy, scientists estimate that only about a thousand of them are Wolf-Rayet stars. NASA notes that among the few hundred Wolf-Rayet binaries observed thus far, Apep is the singular example within our galaxy to contain two Wolf-Rayet stars of these specific types, with most systems featuring only one.

When a pair of Wolf-Rayet stars approach each other, their powerful stellar winds collide and intermingle, resulting in the creation and expulsion of copious amounts of carbon-rich dust for approximately a quarter-century at a time. Previously, only a single shell of this dust around Apep had ever been imaged, though scientists harbored a long-standing belief that additional outer shells existed. Ground-based telescopes, however, proved insufficient for this task. NASA indicates that these newly observed shells were emitted over the past 700 years.

The Webb telescope not only allowed scientists to finally observe more than one dust shell, but it also conclusively affirmed the existence of three gravitationally bound stars within the system. The VLT had initially detected the third star in 2018, but Webb provided the definitive evidence. In the Apep system, the two Wolf-Rayet stars expel dust, which is subsequently “slashed,” as scientists describe it, by the third star—a colossal supergiant. This massive supergiant, through its wider orbit, carves openings into each expanding cloud of dust.

The detailed data provided by Webb also yielded another crucial discovery concerning the stars' orbits. Astronomers were able to precisely determine the frequency with which the pair of Wolf-Rayet stars pass by each other: once every 190 years. During these unusually protracted orbits, the stars maintain close proximity for periods of 25 years.

Yinuo Han, a postdoctoral researcher at Caltech, described the experience of analyzing Webb's new observations as akin to entering a dark room and activating the lights, where everything suddenly becomes visible. Han noted that dust is pervasive throughout Webb's image, and the telescope clearly demonstrates that the majority of it was cast off in regular, predictable patterns.

The two Wolf-Rayet stars, though once more massive than their companion, have shed a significant portion of their mass over an extended period. Nevertheless, scientists estimate that both Wolf-Rayet stars in Apep still possess between 10 and 20 times the Sun's mass, while the supergiant companion is up to 50 times more massive. Eventually, these Wolf-Rayet stars are destined to explode as supernovae, dispersing their residual material into space. There is also a possibility that they could transform into black holes if either star emits a gamma-ray burst.

This pioneering research has been documented in two new scientific papers. Yinuo Han is the lead author of “The Formation and Evolution of Dust in the Colliding-wind Binary Apep Revealed by JWST,” published in The Astrophysical Journal. Concurrently, Ryan White is the lead author of a separate paper, “The Serpent Eating Its Own Tail: Dust Destruction in the Apep Colliding Wind Nebula,” also published this week in The Astrophysical Journal.