JWST observations discover a small star-forming complex
Tomasz Nowakowski
astronomy writer
Stephanie Baum
scientific editor
Robert Egan
associate editor
Using the James Webb Space Telescope (JWST), astronomers have detected what appears to be a faint and small star-forming complex. The discovery of the new complex, which received the designation LAP2, is detailed in a research paper Sept. 8 on the arXiv preprint server.
The hypothetical Population III stars, composed almost entirely of primordial gas, are theorized to be the first stars to form after the Big Bang. Finding very low-metallicity, low-mass sources at high-redshifts could be crucial to investigating these stars, as they provide a rare glimpse of galaxies under conditions similar to those of the early universe. This could help us understand, for instance, how the first generations of stars enriched the cosmos with heavier elements.
Recently, a team of astronomers led by Eros Vanzella of the Astrophysics and Space Science Observatory of Bologna, Italy, inspected one such high-redshift, metal-poor and low-mass source. The source was identified behind the galaxy cluster Abell 2744, which acts as a strong lens.
"We report the discovery of a faint, oxygen-deficient strongly-lensed ionizing source—dubbed LAP2 (Lensed And Pristine 2)—at a spectroscopic redshift of z = 4.19," the researchers explained.
By conducting spectroscopic observations, the astronomers first acquired two mirrored images, LAP2-a and LAP2-b. The large magnification factors of the two images indicate that LAP2 is a tiny and faint star complex with an estimated size of less than 33 light years and intrinsic ultraviolet luminosity of -12.2.
Based on the collected data, the mass of LAP2 was estimated to be a few tens of thousands of solar masses, while its metallicity was found to be less than 0.6% of solar metallicity. The specific star-formation rate (sSFR) of LAP2 was calculated to be 100 per billion years and the age of this complex is assumed to be less than 10 million years.
The metallicity of LAP2 makes it one of the most metal-poor objects known to date. Moreover, the observations suggest that this complex is being caught in an early, pristine formation phase consistent with an instantaneous-burst scenario.
Due to its properties, LAP2 could provide a rare glimpse into galaxies under conditions similar to those of the early universe, occupying a rarely explored regime of low stellar mass. Therefore, the authors of the paper plan more observations of this star-forming complex in order to further explore this matter.
"The system is scheduled to be observed with NIRSpec/IFU in prism mode (Prog. 7677) for a total of 17.4 hours. The resulting two-dimensional maps will enable a direct comparison with the VLT/MUSE IFU Lyα detection, an independent and deeper check of the oxygen deficit in both multiple images, and—by combining them with the data presented here—the possibility of placing more stringent limits on oxygen and other metal lines," the astronomers concluded.
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More information: E. Vanzella et al, A Pristine Star-Forming Complex at z=4.19, arXiv (2025).
Journal information: arXiv
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