A nebula that, instead of being round, takes the shape of a giant egg: this atypical silhouette is the work of a duo of aging celestial bodies that, in tandem, are actively sculpting their environment in their final moments of life.
This cosmic scene is unfolding within the AFGL 4106 system, nestled in a cloud of dust and gas. Using the Very Large Telescope of the European Southern Observatory (ESO), astronomers have captured a detailed image of this pair of stars. The two massive stars, orbiting each other, have reached an advanced stage of their existence and are ejecting immense amounts of matter.
Two aging stars in the binary system AFGL 4106 sculpt a luminous egg-shaped nebula as they approach the end of their lives.
Credit: ESO/G. Tomassini et al.
Unlike our solitary Sun, most stars in the galaxy evolve as couples. These binary systems, where two stars are bound by gravity, are indeed very common. Researchers estimate that a vast majority of stars are born with a companion, or even more rarely, several. Their joint evolution can then profoundly influence their destiny, especially during their final stages.
In the obtained image, the central stars appear as black dots, masked, their brilliance being too intense for the detectors. To highlight the much fainter nebula that surrounds them, scientists used the SPHERE instrument. This equipment is precisely designed to handle high contrast and compensate for atmospheric distortions, thus delivering a sharp view of details once elusive.
The oval aspect of the structure most likely stems from the gravitational interaction between the two stars. Matter ejected by one is deflected and shaped by the presence of the other, giving rise to this asymmetrical morphology.
These results, recently published in the journal
Astronomy & Astrophysics, enrich our knowledge of the final episodes in the lives of massive stars. Observing such systems helps astronomers trace the history of many celestial objects and refine our model of the cosmic matter cycle.
The end of life of massive stars
Stars similar to those in the AFGL 4106 system experience a much shorter and more turbulent existence than our Sun. Their significant mass fuels extremely vigorous nuclear reactions in their cores, depleting their fuel reserve at a frantic pace. After only a few million years, they leave the main sequence to become red giants.
During this stage, the star expands considerably and becomes unstable. It then begins to release its outer layers into space, generating a vast cloud of gas and dust. This phenomenon can last for several thousand years. The ejected matter moves away from the central star, drawing an expanding envelope called a circumstellar nebula.
The star's end depends on its initial mass. For the most massive stars, the core can collapse and trigger a titanic explosion: a supernova. This cataclysm then scatters some of the chemical elements synthesized by the star's core, such as iron or silicon, into the interstellar medium. These elements will later be integrated into new generations of stars and rocky planets and are essential for the emergence of life.
Analyzing these final phases is crucial for tracing the chemical enrichment of the galaxy. Each studied nebula constitutes a record of the mechanisms that occurred within the star. By understanding how these red giants behave and eject their matter, we refine our perception of the origin of the atoms that compose our environment.