JWST and ancient stars

Astronomers use the James Webb Space Telescope as a time machine: because light takes time to travel, Webb can see galaxies as they were more than 13 billion years ago. (nasa.gov) Webb does that in infrared light, the stretched-out glow from very distant objects, and NASA says the telescope is built to study everything from the first luminous glows after the Big Bang to solar systems that could support planets like Earth. (nasa.gov) One target in that search is Population Three stars, the first generation of stars, formed from primordial gas before later stars seeded space with heavier elements such as carbon, oxygen, and silicon. A 2024 Webb study reported a more than 5-sigma detection of helium-II 1640 emission in a clump near the galaxy GN-z11 at redshift 10.6. (arxiv.org) That GN-z11 clump showed no metal lines in the Webb spectrum, and the authors said photoionization by Population Two stars did not fit the data. They estimated a burst with about 200,000 solar masses of stars and said an accreting direct-collapse black hole remained a possible alternative explanation. (arxiv.org) Webb has also found galaxies that are not Population Three systems but may resemble a transition stage. In September 2024, NASA and the European Space Agency said galaxy GS-NDG-9422, seen about 1 billion years after the Big Bang, appears to have gas shining brighter than its stars. (nasa.gov; esa.int) Researchers said models matched GS-NDG-9422 if the galaxy contained unusually hot, massive stars, with temperatures above 80,000 degrees Celsius, compared with roughly 40,000 to 50,000 degrees Celsius for typical hot massive stars nearby. ESA said the Webb data also showed too much chemical complexity for the galaxy itself to host true Population Three stars. (esa.int) The same telescope is also tracing the raw materials of planets in younger systems much closer to home. In the Serpens Nebula, about 1,300 light-years away, Webb observed the protostar EC 53 and found crystalline forsterite and enstatite, plus amorphous olivine and pyroxene, across its disk of gas and dust. (nasa.gov) NASA said those observations showed crystalline silicates forming in the hot inner disk and then being thrown outward to colder regions. That gives astronomers a direct mechanism for how heat-made minerals could end up in comets, a long-running question because comets spend most of their time in the frigid outer Solar System. (nasa.gov) A separate 2025 Nature paper reported refractory solid condensation in an embedded protoplanetary disk, with the authors comparing the process to the formation of refractory solids in the early Solar System. Those are the high-temperature solids that include some of the earliest mineral building blocks preserved in meteorites. (nature.com) Taken together, the Webb results span two ends of the same story: spectra from the first few hundred million years after the Big Bang, and spectra from disks where rocky material is assembling around young stars. The first line of work asks what the earliest stars were like; the second asks how the ingredients that built Earth were sorted, heated, and moved before planets formed. (nasa.gov; nasa.gov)