In the field of one of JWST’s largest-area surveys, COSMOS-Web, an Einstein ring was discovered around a compact, distant galaxy. It turns out to be the most distant gravitational lens ever discovered by a few billion light-years. (Credit: P. van Dokkum et al., Nature Astronomy accepted, 2023)

JWST discovers the farthest gravitational lens ever

A more distant galaxy liked the lens so much that it went and put a ring on it. Here’s the science behind this remarkable cosmic object.

In Einstein’s General Relativity, matter and energy bend spacetime.

An animated look at how spacetime responds as a mass moves through it helps showcase exactly how, qualitatively, it isn’t merely a sheet of fabric. Instead, all of 3D space itself gets curved by the presence and properties of the matter and energy within the Universe. Multiple masses in orbit around one another will cause the emission of gravitational waves, while any light passing through a region that contains this distorted spacetime will be bent, distorted, and possibly magnified by the effects of curved space. (Credit: LucasVB)

Gather sufficient mass in one location, and space will severely distort.

In this image, a massive set of galaxies at the center causes many strong lensing features to appear. Background galaxies have their light bent, stretched, and otherwise distorted into rings and arcs, where it gets magnified by the lens as well. This gravitational lens system is complex, but informative for learning more about Einstein’s relativity in action. (Credit: ESA, NASA, K. Sharon (Tel Aviv University) and E. Ofek (Caltech))

When light passes through that distorted region, bending and magnification ensue.

A distant, background galaxy is lensed so severely by the intervening, galaxy-filled cluster, that three independent images of the background galaxy, with significantly different light-travel times, can all be seen. In theory, a gravitational lens can reveal galaxies that are many times fainter than what could ever be seen without such a lens, but all gravitational lenses only take up a very narrow range of positions on the sky, being localized around individual mass sources. (Credit: NASA & ESA)

It behaves similarly to an optical lens, but powered by gravity: a gravitational lens.

One of the most exciting features found in the El Gordo field, as seen with JWST’s eyes, is the most distant red giant star ever discovered: Quyllur, which is the Quechua term for star. It is the first red giant star found more than 1 billion light-years away, and is actually over 10 billion light-years away. It was only visible due to JWST’s unique capabilities coupled with El Gordo’s gravitational lensing magnification. (Credit: J.M. Diego et al. (PEARLS collaboration), A&A, 2023)