The Ring Nebula, an iconic celestial phenomenon resembling a doughnut, is situated approximately 2,500 light-years away within the constellation Lyra. Astronomers suspect it conceals a mystery that the James Webb Space Telescope, a partnership between NASA and the European and Canadian space agencies, might reveal. Utilizing Webb’s infrared MIRI instrument, researchers acquired a distinct view of the small, hot star at its core.
This core, a white dwarf, is the remnant of a star nearing the end of its life that has lost its outer layers. Upon further examination, scientists found a dust disk encircling the dimming star, akin to those observed around youthful stars in their planet-forming phases. This marks only the second occasion such a disk has been detected around a dying star. While new planets cannot be seen in the nebula’s images, scientists theorize that these conditions could initiate a second generation of planets long after the original ones have formed.
The revelation, published in The Astrophysical Journal, prompts inquiries regarding their nature, formation, longevity, and the potential for a secondary phase of planet formation. In contrast to massive stars that explode into supernovae and transform into black holes, medium-sized stars gradually deplete their nuclear fuel and die more slowly. These stars, like our sun in roughly 5 billion years, evolve into planetary nebulas, a term that can be misleading since it pertains more to stars in decline than to planets.
Scientists have pinpointed several thousand planetary nebulas within the Milky Way, including the Ring Nebula, which is also referred to as NGC 6720 and Messier 57. Utilizing Webb, researchers detected a dense dust cloud surrounding the central white dwarf. “Initially visible as gas-and-dust-rich planet-forming disks in young stellar objects, crucial for star formation,” the authors observed. “Interestingly, dusty disks or disk-like formations emerge again as these stars approach their demise.”
A comparable observation was made previously when astronomers examined the Southern Ring Nebula with Webb, focusing on wavelengths beyond human sight. In the initial images, astronomers were astonished to recognize the actual source of the nebula, according to astronomer Karl Gordon from the Space Telescope Science Institute in Baltimore. “We understood this was a binary star, yet we didn’t perceive much of the actual star responsible for the nebula,” he explained during a news conference in 2022. “However, now with MIRI, this star shines red due to the surrounding dust.”
The dust cloud enveloping the Ring Nebula comprises tiny particles of amorphous silicate, a glass-like substance, as stated in the recent paper. These grains are exceedingly small, potentially less than one-thousandth the thickness of human hair. The cloud itself extends across distances thousands of times greater than that between the Earth and the sun.
Researchers noted another fascinating characteristic at the nebula’s center: the fluctuations in the brightness of the white dwarf. This may suggest the presence of an adjacent star, likely a small red dwarf star. Although scientists have not directly witnessed this companion, they deduce its existence from the patterns observed in the nebula.
The study may corroborate earlier observations that indicated the star had two companions—one distant from the system and another close by. A nearby star could account for the peculiar arcs and rings surrounding the nebula.