Why in news?
A team of Indian astronomers analysing data from NASA’s James Webb Space Telescope has detected molecules called polycyclic aromatic hydrocarbons (PAHs) in the disc of dust and gas surrounding the young star T Chamaeleontis. The discovery attracted attention because these complex carbon‑rich molecules are considered building blocks for life and are rarely seen around low‑mass stars. A partial collapse of the disc’s inner wall allowed ultraviolet light to reach the outer regions, causing the PAH molecules there to glow.
Background
T Chamaeleontis (T Cha) is a sun‑like star located about 350 light years away in the Chamaeleon star‑forming region. With an age of around one million years, the star is surrounded by a transitional disc — a rotating ring of gas and dust with a large gap where planets may be forming. Earlier observations with the Spitzer Space Telescope hinted at the presence of PAHs but the faint signals were difficult to confirm. The new observations, made with Webb’s Mid‑Infrared Instrument, detected strong emission features from PAHs, some containing fewer than 30 carbon atoms.
Key findings
- Disk geometry: Researchers noticed that the inner wall of T Cha’s disc had partially collapsed, allowing ultraviolet radiation from the star to illuminate the outer disc. This illumination excited the PAH molecules, causing them to emit characteristic infrared signals.
- Chemical composition: The detected PAHs are small molecules composed solely of carbon and hydrogen arranged in fused rings. Such molecules are common in space but are usually found around high‑mass stars or within interstellar clouds. Detecting them around a young, low‑mass star like T Cha provides clues about the variety of organic chemistry in planet‑forming discs.
- Persistence over time: Comparison with data from 2002 indicates that the PAH features have persisted for at least two decades, suggesting that the molecules are resilient to changes in the disc’s structure and radiation environment.
- Role of Indian scientists: The study was led by researchers from the Indian Institute of Astrophysics in Bengaluru in collaboration with international partners. Their work highlights India’s growing contribution to space science and astrochemistry.
Significance
- Clues to the origin of life: PAH molecules are precursors to more complex organic compounds that could eventually lead to amino acids and nucleic acids. Finding them in a protoplanetary disc helps scientists understand the chemical conditions from which planets and, potentially, life emerge.
- Insights into disc evolution: The observed collapse of the disc’s inner wall and the survival of PAHs provide evidence that planet formation can rearrange disc structures while preserving sensitive molecules.
- Demonstrating Webb’s capabilities: The detection showcases the sensitivity of the James Webb Space Telescope for studying faint infrared signatures, opening new avenues for observing young stars and their environments.
Conclusion
The discovery of PAH molecules around T Chamaeleontis expands our understanding of the chemical richness of protoplanetary discs. It suggests that even around low‑mass stars, complex carbon‑based molecules can survive and possibly contribute to the ingredients of life. Continued observations with Webb and other observatories will further unravel how these molecules evolve as planets take shape.
Source: PIB
