Universe Today features SKYCR director’s discovery of a gravitational arc in JWST data

The international astronomy outlet Universe Today has published a feature on a new gravitational arc candidate identified in the massive galaxy cluster MACS J0308.9+2645 — a discovery made by Homer Dávila Gutiérrez, astrophysicist and director of SKYCR.ORG, through careful analysis of publicly available James Webb Space Telescope data. The underlying research is posted on the arXiv preprint server.

A discovery hiding in public data

Since JWST became operational in 2022, it has delivered the deepest and clearest views of the cosmos to date. One striking example is the galaxy cluster MACS J0308.9+2645, a deep field whose powerful gravitational field bends and amplifies the light of far more distant galaxies behind it, revealing them as distorted «gravitational arcs.» As it turns out, not all of those arcs had been catalogued.

Searching through JWST archival Near-Infrared Camera (NIRCam) data gathered through Webb’s General Observation program GO-5293, Dávila Gutiérrez identified a previously unrecorded arc candidate, designated A1. He found it after combing through 54 public JWST/NIRCam fields and evaluating 1,591 possible candidates — of which only A1 stood out as a robust arc candidate worth pursuing.

Gravitational lensing, first predicted by Einstein’s general theory of relativity, occurs when a massive foreground object curves the spacetime around it, warping and magnifying the light of objects behind it. Astronomers have used the effect for decades to observe faint, distant sources that would otherwise be invisible.

What makes A1 stand out

As Dávila Gutiérrez explained to Universe Today, three features set A1 apart. Its geometry: the source is extremely elongated, with an axis ratio around 6.5, and aligned tangentially with respect to the cluster center to within about a degree — exactly the orientation gravitational lensing produces. Its brightness: it is the brightest of the highly elongated sources at that radius, which made it measurable. And its absence from every catalogue: it does not appear in the cluster’s published strong-lensing inventory, nor in the SIMBAD, NED, or VizieR databases. When he contacted the GO-5293 team, they confirmed the object did not overlap with the systems they were analyzing.

An initial photometric analysis using the EAZY tool returned a redshift of roughly 4.4, which would have placed A1 within the first billion years of the universe. But here Dávila Gutiérrez emphasized a crucial lesson about method. Automated catalogue photometry — which captures only a small fraction of an extended source’s light — had biased that first estimate toward a much higher redshift. With corrected photometry, A1 is best interpreted as a galaxy at redshift around 1.4, seen as it was roughly 9 billion years ago, lying behind the cluster MACS J0308.9+2645 (itself at redshift 0.356), one of the most massive clusters known.

An evolving analysis

The current working interpretation, shared by the program team’s lensing experts, is that A1 is a singly lensed image: stretched and modestly magnified by the cluster’s gravity, but not multiply imaged. Its projected position, about 51 arcseconds from the cluster’s X-ray center, and its tangential elongation are consistent with that picture. The definitive test — an updated lens model of the cluster built from the new JWST data — is in progress.

The search also turned up a second, fainter candidate designated A2, with geometry similar to A1 but smaller, more elongated, and with less constrained photometry. Dávila Gutiérrez is careful to treat its nature and redshift as open questions, pending the same corrected reanalysis he applied to A1.

For readers of SKYCR, the story carries a double lesson that its director was keen to underline. Genuine discoveries are sitting in already-released Webb data, accessible to any researcher willing to do careful work — but automated catalogue photometry can badly mislead you for extended sources, which makes independent remeasurement, verification, and contact with the original program team essential. As he put it, independent researchers and program teams collaborating over public data is Webb’s archive working exactly as intended.

© 2026 Homer Dávila Gutiérrez, FRAS — SKYCR.ORG. All rights reserved. Publication: Homer Dávila Gutiérrez, Discovery of a gravitational arc candidate at photometric redshift 4.4 in MACS J0308.9+2645 from a catalogue-based search of JWST imaging, arXiv (2026). DOI: 10.48550/arXiv.2607.12129