Gravitational Lensing in Galaxy Clusters

Galaxy clusters, the most massive bound structures in the Universe, act as powerful gravitational lenses by bending and magnifying the light from background galaxies. This phenomenon arises from the curvature of spacetime induced by the cluster’s total mass, including dark matter, gas and galaxies. Gravitational lensing manifests in two regimes: strong lensing, producing multiple, highly distorted arcs and rings close to the cluster core; and weak lensing, causing subtle shape distortions over wider fields. Together, these effects offer complementary probes of cluster mass distributions on scales ranging from tens to thousands of kiloparsecs. Strong lensing enables detailed reconstruction of the inner density profiles and detection of substructures, while weak lensing traces the smoother, larger‐scale dark matter halo. The observed magnification of distant sources has opened a window on the high‐redshift Universe, revealing galaxies that would otherwise be too faint to detect. Beyond mapping dark matter, cluster lensing constrains cosmological parameters such as the Hubble constant and the dark energy equation of state. Recent advances in high‐resolution imaging and spectroscopic follow‐up, particularly with facilities such as the Hubble Space Telescope and the James Webb Space Telescope, have refined lens models and uncovered unprecedented fine‐scale features, including microlensing by intracluster stars and caustic‐crossing events. Consequently, gravitational lensing in galaxy clusters remains at the forefront of both astrophysical and cosmological research, linking the study of large‐scale structure formation with investigations of the early Universe.

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Gravitational Lensing in Galaxy Clusters publication trend

The graph below shows the total number of articles in gravitational lensing in galaxy clusters across all publications each year (not limited to Nature Index journals).

Technical terms

Strong lensing: A regime of gravitational lensing where light deflection by a massive object produces multiple, highly distorted or magnified images of a single background source.

Weak lensing: A lensing regime characterised by subtle, coherent distortions in the shapes of background galaxies, used statistically to map large‐scale mass distributions.

Critical curve: A contour in the lens plane along which the magnification of a background source formally diverges, corresponding to caustics in the source plane.

Caustic: The envelope of lightrays in the source plane where magnification becomes formally infinite, marking regions of highly amplified images.

Magnification map: A spatial representation of the lensing magnification factor across the field of view, used to recover the true brightness and size of background sources.

Einstein radius: A characteristic angular scale of strong lensing, defining the radius at which a circularly symmetric lens would produce a ring image of a source located directly behind it.

References

1. Strong Lensing by Galaxy Clusters. Space Science Reviews (2024).
2. The GLASS-JWST Early Release Science Program. III. Strong-lensing Model of Abell 2744 and Its Infalling Regions. The Astrophysical Journal (2023).
3. Dark Matter under the Microscope: Constraining Compact Dark Matter with Caustic Crossing Events. The Astrophysical Journal (2018).
4. HUBBLE SPACE TELESCOPE COMBINED STRONG AND WEAK LENSING ANALYSIS OF THE CLASH SAMPLE: MASS AND MAGNIFICATION MODELS AND SYSTEMATIC UNCERTAINTIES. The Astrophysical Journal (2015).