An international team used the Multi Unit Spectroscopic Explorer, or MUSE, on the European Southern Observatory’s Very Large Telescope to examine 76 possible strong gravitational lenses. A residual neural network had selected the candidates from images collected by the DESI Legacy Imaging Surveys.
The peer-reviewed study, published in The Astrophysical Journal Supplement Series, fully confirmed 55 systems. That is narrower than the 70-lens figure highlighted in the NSF NOIRLab report distributed by Phys.org: the paper says 15 of those systems still need more observations.
How the candidates were checked
A strong gravitational lens appears when a massive foreground object, such as a galaxy, bends light from a more distant source. The distorted background object can show up as arcs, rings or multiple images. Similar-looking structures are not always evidence of lensing, so images alone cannot settle every candidate.
MUSE is an integral-field spectrograph, meaning it records a spectrum at each point across an image. Those spectra let researchers estimate how far away different objects are by measuring their redshifts. A genuine lensing configuration requires the source to sit behind the foreground lens.
The team made 92 MUSE pointings from 2022 through 2024 and extracted spectra for 223 objects in the observed fields. In 55 of the 76 candidate systems, the researchers measured redshifts for both the foreground lens and the background source. The paper classifies those systems as fully confirmed.
Fifteen systems still need follow-up
For another 15 candidates, the team measured only the redshift of the foreground galaxy. The background sources were too faint, lacked prominent spectral features or were not visible clearly enough in data taken under unfavorable weather. The paper says those systems require additional observations before they can be confirmed.
The remaining six candidates were ruled out. Spectroscopy showed that apparent arcs or multiple objects were actually spiral arms or unrelated foreground and background objects rather than gravitationally lensed sources.
Confirmed strong lenses give astronomers natural magnifying glasses for studying distant galaxies. Larger, well-characterized samples can also support future work on dark-matter distributions, galaxy structure and measurements of cosmic expansion. Those are potential uses of the catalog; this study focused on checking which candidates were real.
