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upstart writes:

Short-cut method pinpoints a galaxy apparently formed from just hydrogen and helium:

Staring deep into space and far back in time, a team of astronomers may have spotted a galaxy full of stars made from only the primordial gas created in the Big Bang. Such "population III stars" would have formed from hydrogen and helium and nothing else, and researchers have been searching for them for decades, racking up many disputed sightings. If confirmed, the discovery, made with NASA's JWST space observatory, opens a window on the starting point of the chemical enrichment of the universe, in which the heavier elements needed to make planets and life began to be forged in stellar explosions.

"It's very exciting," says astronomer Elka Rusta of the University of Florence. "We hypothesize that [population III stars] exist from theory, but they have never been directly observed."

The nature of population III stars remains uncertain. Most theorists think they were huge, with masses up to 1000 times that of the Sun, 10 times larger than any star around today. That's because a cloud of gas collapsing to form a star needs to cool, which requires ionizing the atoms in the gas when they collide. But tightly bound hydrogen and helium atoms are hard to ionize, unlike the heavier elements found in later generations of stars. So a cloud of primordial gas would just keep growing as it pulled in more gas under its own gravity, reaching an enormous size before finally becoming dense enough to ignite nuclear fusion in its core.

The gigantic stars that resulted would also burn hot and fast, ending in a supernova explosion after just a few million years. That brief first flash of population III stars is hard for astronomers to spot in galaxies that went on to shine steadily for billions of years with smaller, longer lived stars. But the spectrum of the light from the giant stars might give them away. Different elements absorb and emit characteristic wavelengths of light. Population III stars would produce very strong emission lines for hydrogen and helium and would lack completely spectral lines produced by heavier elements.

[...] The team still refers to it as a candidate because without a detailed spectrum it's impossible to rule out other, less exciting possibilities. For example, GLIMPSE-16043 could be a cloud of lingering primordial gas that is being energized by light from a black hole gorging on matter. Or it could simply be a smaller cluster of stars much closer to Earth that is mimicking a population III spectrum. To settle the issue, "ultimately, you will need spectroscopy," Sobral says. Naidu says JWST officials have awarded the project some high-priority observing time in June to get a spectrum.

If population III stars prove to be big and bright, the ultraviolet light they emit could have played a key role in the youthful universe: ionizing the neutral hydrogen gas between galaxies. And small primordial galaxies like GLIMPSE-16043 could be the predecessors of ultrafaint dwarf galaxies close to our own Milky Way that appear to contain very ancient stars only slightly enriched by heavier elements, notes Tim Beers of the University of Notre Dame. Some astrophysicists think those current stars are the children of population III stars, Beers says, and by studying them astrophysicists could learn about their ancient forebears. "I find it exciting that you can draw a straight line from what we see around the Milky Way to this proposed birthplace."

arXiv Reference: https://doi.org/10.48550/arXiv.2501.11678

Original Submission