Research

When two galaxies in the sky perfectly line up in the sky, we can see images of the background galaxy (source) as its light bends around the foreground galaxy (lens), known as strong gravitational lensing. This phenomenon was predicted using Einstein's theory of General Relativity and observed for the first time in 1979. With certain objects, such as quasars, we see multiple clear images of the source. The difference in time that it takes light to travel different paths around the lens gives us insight into the matter distribution within the lens, as well as cosmological parameters such as the Hubble constant. The study of this process is known as Time-Delay Cosmography.

Weak gravitational lensing is a phenomenon in which light from distant galaxies is subtly distorted by the gravitational influence of large-scale structures, such as dark matter and galaxy clusters, as it travels through the universe. Unlike strong lensing, which produces dramatic arcs and multiple images, weak lensing causes small distortions in background galaxies. These distortions are too small to detect in individual galaxies, so astronomers perform a statistical analysis over large samples. Weak lensing is sensitive to all matter (dark and luminous), making it a powerful cosmological probe. It can be used to measure the growth of structure in the universe, constraining key parameters such as the matter density of the universe and properties of dark energy. 

Cosmological redshift is the stretching of light from distant galaxies due to the expansion of the universe. As the universe grows, the wavelength of photons traveling through space increases, shifting their light toward the red end of the spectrum. By analyzing the spectra of galaxies, astronomers identify known spectral features, such as emission or absorption lines, and measure how far they’ve shifted from their expected wavelengths. This determines a galaxy’s redshift, which in turn provides its distance through Hubble’s law. Redshift measurements are essential for mapping the 3D structure of the universe and tracing its expansion history. Large surveys, such as SDSS, DESI, and Euclid, collect spectra for millions of galaxies. These data are used to study large-scale structure, galaxy evolution, and the effects of dark energy.