Webb confirms disks lasted longer in early universe conditions
Planet formation found possible in low-metal environments
Findings reshape theories on planet-forming disk lifespans
James Webb's image of NGC 346 shows a star cluster with ten surveyed stars marked.
Photo Credit: NASA, ESA, CSA, STScI
The NASA/ESA/CSA James Webb Space Telescope has verified a decades-old mystery regarding planet formation in the early universe. According to The Astrophysical Journal, findings indicate that planet-forming disks around stars endured far longer than previously theorised, even in environments with minimal heavy elements.
Reportedly, in 2003, the NASA/ESA Hubble Space Telescope observed the presence of massive planets around ancient stars. This was surprising as these stars lacked heavier elements like carbon and iron, essential for planet formation. The discovery raised questions about how such planets could form and grow so early in the universe's history.
Revisiting a Longstanding Puzzle
To explore this further, the Webb Telescope focused on NGC 346, a massive star cluster in the Small Magellanic Cloud. As one of the Milky Way's nearest neighbours, its chemical composition, dominated by hydrogen and helium, closely resembles conditions in the early universe. The cluster's stars, estimated to be between 20 to 30 million years old, were found to retain planet-forming disks far beyond the expected timeframes seen in our galaxy.
Guido De Marchi, study lead from the European Space Research and Technology Centre (ESTEC), stated to ESA sources that they see that disks indeed surround these stars and are still in the process of gobbling material, even at the relatively old age of 20 or 30 million years. This finding challenges current models, which predict that planet-forming disks dissipate within a few million years. Elena Sabbi, co-investigator and chief scientist at NOIRLab's Gemini Observatory, explained in a statement that models suggested disks would not survive in environments with low metal content. Webb has now proven that planets in such conditions can form and evolve for longer periods.
Why Do Disks Persist Longer?
Two possible explanations have been proposed for the extended lifespans of these disks. The first suggests that radiation pressure, which typically disperses disks, is less effective in environments with minimal heavier elements. These elements are needed for radiation to interact with the surrounding gas efficiently.
The second explanation considers the initial size of gas clouds. Stars forming in low-metal environments might originate from larger clouds of gas, leading to bigger disks. Larger disks take significantly longer to disperse, providing more time for planet formation.
These observations provide new insights into planet formation in the early universe, indicating that planets may have had extended growth periods even under conditions once thought unfavourable. With Webb's unprecedented resolution, astronomers now have tangible evidence that planet-forming disks are far more resilient than previously understood, reshaping long-standing theories about planetary evolution.
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