Weak Gravitational Lensing in Cosmological Observations

Weak gravitational lensing arises from the minute deflection of light from distant galaxies by the gravitational potential of intervening large-scale structure. The coherent distortions in galaxy shapes—known as cosmic shear—encode information on the distribution of dark matter, the growth of structure and the geometry of the Universe. Recent advances in wide-field imaging and shape-measurement algorithms have enabled surveys to map the projected mass distribution over vast areas of sky, yielding direct probes of dark energy through the evolution of structure formation. Key challenges in these analyses include the accurate determination of galaxy shapes in the presence of instrumental and atmospheric point-spread functions, the separation of lensing signals from intrinsic alignments of galaxies and the calibration of photometric redshifts. By combining shear measurements across multiple redshift bins—cosmic shear tomography—observers extract the matter power spectrum as a function of time, constraining fundamental cosmological parameters such as the matter density, clustering amplitude and the dark energy equation of state. The synergy of lensing with complementary probes—such as baryon acoustic oscillations, galaxy clustering and cluster mass estimates—enhances the robustness of cosmological inferences and tests models of gravity beyond General Relativity.

Research from Nature Portfolio

Recent studies have revealed a detectable baryon acoustic oscillation feature in the cross-correlation of galaxy positions and galaxy ellipticities, demonstrating the viability of lensing-induced shape correlations as a standard ruler. By analysing spectroscopic samples combined with deep imaging surveys, researchers have measured the galaxy–ellipticity cross-correlation function at intermediate redshifts and modelled it with linear alignment schemes. This approach has achieved a 3–5 % precision on comoving distance measurements and yielded a ~10 % reduction in uncertainty when added to traditional galaxy clustering analyses. Such independent shape-based distance indicators are expected to play a pivotal role in mitigating systematics in forthcoming wide-field experiments.

Weak Gravitational Lensing in Cosmological Observations publication trend

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

Technical terms

Cosmic shear: Coherent distortion of background galaxy shapes due to weak lensing by intervening matter.

Convergence: Projected surface mass density along the line of sight, related to magnification of galaxy images.

Shear: Anisotropic stretching of galaxy images, described by two orthogonal components.

Cosmic shear tomography: Division of source galaxies into redshift bins to study the evolution of lensing power spectra over cosmic time.

Intrinsic alignment: Physical correlation of galaxy shapes with local tidal fields, which can mimic or bias lensing signals.

Photometric redshift: Estimated galaxy redshift derived from multi-band photometry rather than spectroscopy, subject to calibration uncertainties.

Baryon acoustic oscillations: Regular, periodic fluctuations in the density of the visible baryonic matter of the Universe, used as a standard ruler.

Point-spread function (PSF): Response of an imaging system to a point source, requiring accurate modelling to correct observed galaxy shapes.

References

1. First Constraints on Growth Rate from Redshift-space Ellipticity Correlations of SDSS Galaxies at 0.16. The Astrophysical Journal Letters (2023).
2. Evidence for baryon acoustic oscillations from galaxy–ellipticity correlations. Nature Astronomy (2023).
3. Euclid. Astronomy & Astrophysics (2025).
4. KiDS+VIKING-450: Cosmic shear tomography with optical and infrared data⋆. Astronomy & Astrophysics (2020).