Stars form from giant clouds of gas and dust that begin to collapse under their own gravity. As this cloud spins, it flattens into a disk with the young star forming at the center. Around the star, bits of dust start sticking together, slowly building up into pebbles, then boulders, and eventually full-sized planets. The inner planets tend to be rocky because radiation pressure drives away lighter elements, while the outer planets can grow into gas giants. It’s a chaotic process that takes millions of years, with planets jostling for position and sometimes even getting kicked out of their system. This is not just theory however as we can see it happening across the Galaxy.
Until recently it was thought that protoplanetary disks disappear after about 10 million years. However a team of researchers at the University of Arizona have made a surprising discovery about planetary formation; the disks can remain for much longer provided the stars are one-tenth the mass of the Sun, or smaller. The paper was published in the Astrophysical Letters Journal, by a team led by Feng Long from the university’s Lunar and Planetary Laboratory. The team has analysed a 30-million-year-old protoplanetary disk using the James Webb Space Telescope in the first detailed chemical analysis of such a long-lived disk.
The team theorise that while high-energy radiation from young stars usually clears out planet-forming disks, stars below a certain mass threshold maintain these disks much longer. They studied J0446B, a star in the constellation Columba about 267 light-years away, which has unexpectedly retained its protoplanetary disk for much longer than usual. Despite its advanced age, the disk’s chemical composition remains largely unchanged compared to younger disks.
The study confirmed that the disk around J0446B is not a debris disk (which would contain secondary material from asteroid collisions) but confirmed it is a primordial disk, as evidenced by the presence of hydrogen and neon gases. This discovery of a long-lived gas-rich disk has tantalising implications for the search for extraterrestrial life. There is particularly interest in how this might relate to systems like TRAPPIST-1, 40 light years away, which features a red dwarf star with seven Earth-sized planets, three of which orbit in the habitable zone. It’s here where liquid water could exist, creating potential conditions for life to develop.
The TRAPPIST-1 system of planets (Credit : NASA/JPL-Caltech)
The work provides a valuable insight into stellar and planetary system evolution. and the researchers emphasise that fully understanding them is particularly important because low-mass stars are thought to be far more numerous than sun-like stars throughout the universe. As Feng Long noted, studying these enduring disks helps “fill out the blanks in the photo album of the Universe.”
Source : James Webb Telescope reveals planet-forming disks can last longer than previously thought
