Using the first science image released by the James Webb Space Telescope (JWST) this month, an international team of scientists led by the Max Planck Institute for Astrophysics has built an improved model for the mass distribution of the galaxy cluster SMACS J0723.3−7327. They used dozens of multiple images of far-away background galaxies revealed in the JWST image, some of which were too faint to be detected previously. Acting as a so-called gravitational lens, the foreground galaxy cluster produces both multiple images of background galaxies and magnifies these images. One family of such multiple images belongs to a galaxy, which the model predicts to be at a distance of about 13 Gyrs, i.e. whose light travelled some 13 billion years before reaching the telescope. If confirmed, this will emphasise the importance of accurate gravitational lens models for the identification of distant galaxies and their detailed study.
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