Gravitational Lensing Windows

Galaxy clusters act as enormous gravitational lenses, bending and magnifying light from galaxies far behind them. This warps background galaxies into arcs, rings, and multiple images that would otherwise be too faint to see, turning each cluster into a natural telescope.

The Hubble Frontier Fields program aimed at six massive clusters as cosmic magnifying glasses. The JWST has pushed further, using cluster lensing to catch galaxies from the first few hundred million years after the Big Bang.