A new image captured by the James Webb Space Telescope (JWST) reveals a massive star located on the distant outskirts of our Milky Way galaxy, emitting a powerful cosmic blowtorch. This stunning observation was made using the JWST's Near-Infrared Camera, showcasing two energetic jets colliding with the surrounding interstellar medium, creating the intricate nebulous formation known as Sharpless 2-284, or Sh2-284 for short.
The jets from this massive star stretch across an impressive eight light-years and expand at astonishing velocities of hundreds of thousands of miles per hour. The mere existence of these jets serves as a testament to understanding the formation process of the most massive stars in the universe. Jonathan Tan from the University of Virginia and Chalmers University of Technology noted, "Once we found a massive star launching these jets, we realized we could use the Webb observations to test theories of massive-star formation."
Typically, stellar jets are associated with lower mass stars during their formation stages. These jets are powered by material, predominantly hydrogen gas, that falls onto the developing star. This inflowing material creates a disk around the young protostar. As some of this material is absorbed by the star, increasing its mass, excess material is expelled through tightly wound magnetic fields, projecting it outwards in two directed jets along the star's axis.
While low-mass stars tend to form in a relatively orderly manner, the formation of more massive stars—those that eventually become supernovae—has been theorized to be more chaotic. This chaos could cause the star and its accretion disk to wobble, resulting in jets that are less uniform and more dispersed. However, the JWST imagery of Sh2-284 shows straight, well-aligned jets that are almost 180 degrees apart, suggesting a more stable formation process.
According to the models of star formation, the size of the jets correlates with the mass of the star producing them. Current estimates suggest that the star at the center of Sh2-284 is approximately ten times the mass of our sun and continues to grow, actively powering its outflow. Tan remarked, "How energetic these jets are, how straight, how narrowly collimated, and their ages can all help astronomers better understand the environment in which stars sourcing those jets form, as well as the intrinsic properties of such stars."
Yu Cheng from the National Astronomical Observatory of Japan, who led the JWST observations, expressed the importance of this finding, stating, "We didn’t really know there was a massive star with this kind of super-jet out there before the observation." The spectacular outflow of molecular hydrogen from a massive star like this is quite rare in other regions of the galaxy.
Sh2-284 is situated about 15,000 light-years from Earth, on the outskirts of the Milky Way's spiral disk. This region is characterized by a lower abundance of elements heavier than hydrogen and helium—referred to as "metals" by astronomers. These elements are typically formed within stars, and the lack of vigorous star formation in this galaxy region results in fewer of these elements being produced. Cheng noted, "To find a star forming in this low metallicity environment is fortunate for astronomers, because these conditions mimic those found in the early universe."
The history of Sh2-284 is fascinating, with the tips of the jets representing the oldest material expelled by the star. Over a timespan of more than 100,000 years, this material has been ejected, while younger outflows appear in the area behind the jets. Tan elaborated, "Originally the material in the tips was close to the star, but over time, the tips were propagating out." Although the growing star itself is not directly visible, the JWST captures the structure of Sh2-284 with its filaments, knots, bow shocks, and linear chains of clumpy material arising from the jets' interactions with the interstellar medium.
Despite the impressive power and beauty of these jets, they are transient phenomena. Eventually, the star will emerge from its cocoon, fully developed and potentially possessing tens of times the mass of our sun. Its lifespan will be limited to just a few million years before it explodes, creating a new nebula—a star-death event rather than a birth. However, the legacy of this massive star will enrich the cosmos with the metals it has forged, perpetuating the cycle of stellar evolution.
