Free Astronomy Magazine March-April 2025

33 MARCH-APRIL 2025 few heavier elements such as carbon and iron, which came later through supernova explosions. “Current models predict that with so few heavier elements, the disks around stars have a short lifetime, so short in fact that planets cannot grow big,” said the Webb study’s co-investigator Elena Sabbi, chief scientist for Gemini Observatory at the National Science Foundation’s NOIRLab in Tucson. “But Hubble did see those planets, so what if the models were not correct and disks could live longer?” To test this idea, scientists trained Webb on the Small Magellanic Cloud, a dwarf galaxy that is one of the Milky Way’s nearest neighbors. In particular, they examined the massive, star-forming cluster NGC 346, which also has a relative lack of heavier elements. The cluster served as a nearby proxy for studying stellar environments with similar condi- tions in the early, distant universe. Hubble observations of NGC 346 from the mid 2000 revealed many stars about 20 to 30 million years old that seemed to still have planet- forming disks around them. This went against the conventional be- lief that such disks would dissipate after 2 or 3 million years. “The Hubble findings were contro- versial, going against not only em- pirical evidence in our galaxy but also against the current models,” said De Marchi. “This was intrigu- ing, but without a way to obtain spectra of those stars, we could not really establish whether we were witnessing genuine accretion and the presence of disks, or just some artificial effects.” Now, thanks to Webb’s sensitivity and resolution, scientists have the first-ever spectra of forming, Sun- like stars and their immediate envi- ronments in a nearby galaxy. “We see that these stars are indeed surrounded by disks and are still in by NASA/ESA/CSA Ann Jenkins Christine Pulliam N ASA’s James Webb Space Tel- escope just solved a conun- drum by proving a controver- sial finding made with the agency’s Hubble Space Telescope more than 20 years ago. In 2003, Hubble provided evidence of a massive planet around a very old star, almost as old as the uni- verse. Such stars possess only small amounts of heavier elements that are the building blocks of planets. This implied that some planet for- mation happened when our uni- verse was very young, and those planets had time to form and grow big inside their primordial disks, even bigger than Jupiter. But how? This was puzzling. To answer this question, researchers used Webb to study stars in a nearby galaxy that, much like the early uni- verse, lacks large amounts of heavy elements. They found that not only do some stars there have planet- forming disks, but that those disks are longer-lived than those seen around young stars in our Milky Way galaxy. “With Webb, we have a re- ally strong confirmation of what we saw with Hubble, and we must re- think how we model planet forma- tion and early evolution in the young universe,” said study leader Guido De Marchi of the European Space Research and Technol- ogy Centre in N o o r d w i j k , Netherlands. In the early universe, stars formed from mostly hydro- gen and he- lium, and very T his is a James Webb Space Telescope image of NGC 346, a massive star cluster in the Small Magellanic Cloud, a dwarf galaxy that is one of the Milky Way’s nearest neighbors. With its relative lack of elements heavier than hydrogen and he- lium, the NGC 346 cluster serves as a nearby proxy for study- ing stellar environments with similar conditions in the early, distant universe. Ten, small, yellow circles overlaid on the image indicate the positions of the ten stars surveyed in this study. [NASA, ESA, CSA, STScI, Olivia C. Jones (UK ATC), Guido De Marchi (ESTEC), Margaret Meixner (USRA)]