Gravitational Lensing with JWST

Gravitational Lensing using #JWST

Gravitational lensing is an effect on light from a background source that arises as a result of the curvature of spacetime, the three dimensions of space and time united into a single entity, caused by mass.

A gravitational lens is matter, such as a cluster of galaxies or a point particle, that bends light from a distant source as it travels toward an observer. The amount of gravitational lensing is described by Albert Einstein's general theory of relativity

When a Telescope lines up with a gravitational lens, it becomes an incredibly powerful telescope, in which case you are using the gravity of an entire cluster of galaxies as a natural telescope. James Webb was able to see multiple versions of the same supernova going off in a galaxy as a result of this gravitational lens.

The light had to follow a different path around this gravitational lens or galaxy cluster. So astronomers were able to see a type one supernova go off in a galaxy that was lensed by a galaxy cluster, and they were able to see it go off multiple times, depending on the length of the journey that the light had to take to go around the galaxy.

Galaxy clusters are the most massive structures in the Universe and are therefore powerful cosmic telescopes for observing faint and distant sources via the gravitational lensing effect.

When a background source galaxy lies behind a galaxy cluster, the light rays that we see from the source are deflected by the gravitational potential of the foreground galaxy cluster, that is, the source is gravitationally lensed by the cluster.

In the regime of strong lensing, we see multiple magnified and distorted images of the background source. The lensing magnifications produced by galaxy clusters can reach factors of ∼100 − 1000, allowing us to detect the faintest sources, which would otherwise be impossible. The positions and morphologies of the multiple lensed images also allow us to probe the distribution of matter, particularly dark matter, in the galaxy cluster, which is crucial for understanding the nature of dark matter. Furthermore, an individual galaxy cluster often lenses several background sources into several corresponding ‘families’ of multiple images that straddle different locations around the galaxy cluster. Families of multiple images formed by sources of different redshifts provide measurements of angular diameter distance ratios between the cluster and sources, allowing us to probe the geometry of the Universe. In cases where a background source is time varying, such as a quasar or supernova, the time delay(s) between the multiple images provide measurements of the ‘time-delay distance’ and the Hubble constant that sets the expansion rate of the Universe. Strong lensing galaxy clusters are therefore excellent laboratories for astrophysical and cosmological studies.

The James Webb Space Telescope (#JWST;) operating in the infrared will provide unprecedented observations of high-redshift galaxies, in terms of both sensitivity and angular resolution. Studying these distant galaxies is crucial for understanding how the first galaxies formed and evolved into the structures that we see today. These first galaxies are inherently faint, and the combination of JWST and galaxy cluster lensing is therefore the best way to detect and study these faintest galaxies. As part of the Early Release Observations (ERO), the JWST team publicly released the observations of its first cosmic targets, including the galaxy cluster. In this Letter we demonstrate the power of strong gravitational lensing and JWST to unveil and study faint distant galaxies. In particular, we identify new sources in the JWST images that were previously undetected in Hubble Space Telescope (HST) imaging, more than doubling the number of families of multiple images. Even though these new families of images do not yet have spectroscopic redshifts, we demonstrate the utility of our cluster lens mass model to constrain the redshifts of these new source galaxies, including one at z # 6.