For the first time, cosmic dust particles that play a critical role in the formation of planets around young stars have been observed being formed, thanks to the advanced capabilities of the James Webb Space Telescope (JWST). This remarkable discovery marks a significant advancement in our understanding of how the basic materials necessary for planet formation come together, as noted by Mikako Matsuura from Cardiff University, who spearheaded the new JWST observations.
The Butterfly Nebula, also known as NGC 6302, is located approximately 3,400 light-years away in the constellation of Scorpius. This exquisite celestial body is classified as a planetary nebula, representing the final stages of a sun-like star that has exhausted its hydrogen supply for nuclear fusion and has reached the end of its life cycle. In this process, the outer layers of the star are expelled into space, forming the nebula, while the incredibly hot core, radiating at a staggering 220,000 degrees Celsius (396,000 degrees Fahrenheit), remains as a white dwarf.
The Butterfly Nebula exhibits a bi-polar structure, with two prominent lobes that resemble wings. At the center lies a torus of dark dust, viewed edge-on, which is the focus of the JWST's imaging. Utilizing its Mid-Infrared Instrument (MIRI) and supplemented by data from the ALMA radio telescope, the JWST has targeted this central torus, revealing new insights into the dust composition within.
Typically, interstellar dust measures up to 0.1 microns (ten millionths of a meter) in size. However, the MIRI instrument detected grains of crystalline silicate dust within the Butterfly Nebula's torus that are considerably larger, measuring about a millionth of a meter. While still tiny, these grains are comparable to those found in star- and planet-forming regions, suggesting that the process of dust accumulation is underway.
The presence of larger dust grains marks the initial stages of the planet-building process. Dust found in molecular gas clouds, which give rise to new star systems, originates from the remnants of previous generations of stars. As this dust disperses into interstellar space, it contributes to the gas clouds responsible for forming new stars. The formation of larger dust grains, essential for creating planets, has remained somewhat enigmatic — until now.
For years, scientists have speculated about the mechanisms behind cosmic dust formation. With the powerful capabilities of the JWST, we are beginning to unravel this mystery. The size of the dust grains observed in the Butterfly Nebula indicates that they have been growing for an extended period, partially due to chemical reactions stimulated by the intense heat of the white dwarf at the nebula's core.
Among the findings, the JWST identified grains of quartz crystals within the dusty torus of the Butterfly Nebula. Matsuura remarked on the diverse nature of the dust, stating, "We were able to see both cool gemstones formed in calm, long-lasting zones and fiery grime created in violent, fast-moving parts of space, all within a single object." Additionally, the observations uncovered the presence of polycyclic aromatic hydrocarbons (PAHs), common carbon-based molecules that can be found on Earth in substances like burnt toast and car exhaust fumes. PAHs are suspected to play a crucial role in the chemistry of star- and planet-forming regions, and potentially in prebiotic chemistry that leads to the emergence of life.
As time progresses, the brilliance of the Butterfly Nebula will gradually disperse into the expanse of deep space. The PAHs, quartz grains, and other molecules that emerged from the star's demise will drift among the stars, seeking a new home in a gas cloud where they can contribute to the birth of a new system of stars and planets. This discovery not only enhances our understanding of cosmic processes but also opens new avenues for exploring the origins of planetary systems.
