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Starts With A Bang

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.
most distant gravitational lens
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
Key Takeaways
  • According to Einstein’s general theory of relativity, matter and energy deform the fabric of spacetime. If enough mass gathers together in one place, it can behave as a gravitational lens.
  • Distorting and magnifying the light from background galaxies, these gravitational lenses can create arcs, multiple images, and in the case of a perfect alignment, an “Einstein ring.”
  • With brand new JWST data, astronomers have now identified the most distant gravitational lens ever, and it just happens to come with a perfect Einstein ring. Here’s its cosmic story, so far.

In Einstein’s general relativity, matter and energy bend spacetime.

General relativity curved space time
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.

galaxy cluster colors
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.

gravitational lens example
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 in 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.

lensed star Quyllur El Gordo
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 it’s 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

When the observer, lens, and background objects all align, spectacular features emerge.

gravitational lens illustration
An illustration of gravitational lensing showcases how background galaxies — or any light path — is distorted by the presence of an intervening mass, but it also shows how space itself is bent and distorted by the presence of the foreground mass itself. When multiple background objects are aligned with the same foreground lens, multiple sets of multiple images can be seen by a properly-aligned observer, or even an “Einstein ring” in the case of perfect alignment. If a transient event, like a supernova, occurs in the background galaxy, it will appear with time delays in the various images.
Credit: NASA, ESA & L. Calçada

Arcs, multiple images, and even complete rings all become possible.

This side-by-side view of galaxy cluster SMACS 0723 shows the MIRI (left) and NIRCam (right) views of this region from JWST. Note that although there’s a bright galaxy cluster at the center of the image, the most interesting objects are gravitationally lensed, distorted, and magnified by the cluster itself, and are located far more distant than the cluster itself.

Most often, galaxy clusters make the best gravitational lenses, containing overwhelmingly large masses.

the fishhook within el gordo
The triply lensed galaxy shown here is known as the Fishhook, after its unique appearance shaped by the foreground gravitational lens. While the entire foreground cluster, El Gordo, lenses the background galaxy, it’s the prominent double galaxy in the foreground cluster that provides the Fishhook with its remarkable appearance.
Credit: Jose M. Diego (IFCA), Brenda Frye (University of Arizona), Patrick Kamieneski (ASU), Tim Carleton (ASU), Rogier Windhorst (ASU); Processing: Alyssa Pagan (STScI), Jake Summers (ASU), Jordan C. J. D’Silva (UWA), Anton M. Koekemoer (STScI), Aaron Robotham (UWA), Rogier Windhorst (ASU)

But individually massive, compact galaxies can theoretically serve as gravitational lenses, too.

strong gravitational lensing horseshoe
This object isn’t a single ring galaxy, but rather two galaxies at very different distances from one another: a nearby red galaxy and a more distant blue galaxy that’s gravitationally lensed by the foreground galaxy’s mass. These objects are simply along the same line of sight, with the background galaxy’s light gravitationally distorted, stretched, and magnified by the foreground galaxy. The result is a near-perfect ring, which would be known as an Einstein ring if it made a full 360 degree circle. While lensing is more commonly seen from galaxy clusters, individual galaxies can do it if they’re compact enough and if the alignment is right.
Credit: ESA/Hubble & NASA

Such galaxies are rare today, but massive, compact galaxies were common 10-12 billion years ago.

flight through universe CEERS JWST NASA
Taking us beyond the limits of any prior observatory, including all of the ground-based telescopes on Earth as well as Hubble, NASA’s JWST has shown us the most distant galaxies in the Universe ever discovered. If we assign 3D positions to the galaxies that have been sufficiently observed-and-measured, we can construct a visualized fly-through of the Universe, as the CEERS data from JWST enables us to do here. At greater distances, compact, star-forming galaxies are more common; at closer distances, more diffuse, quiescent galaxies are the norm.
Credits: Frank Summers (STScI), Greg Bacon (STScI), Joseph DePasquale (STScI), Leah Hustak (STScI), Joseph Olmsted (STScI), Alyssa Pagan (STScI); Science by: Steve Finkelstein (UT Austin), Rebecca Larson (RIT), Micaela Bagley (UT Austin)

Caught by JWST’s eyes, a distant massive, compact galaxy was found behaving as a gravitational lens.

gravitational lens einstein ring
This gravitationally lensed system from the COSMOS-Web field consists of a compact, massive galaxy located ~17 billion light-years away, and a more distant galaxy 21 billion light-years away whose light is stretched into a ring-like shape. The decomposition of the two components is shown at bottom.
Credit: P. van Dokkum et al., Nature Astronomy accepted, 2023

The lens itself is 17 billion light-years away: 2.3 billion more distant than the prior record-holder.

A farthest gravitational lens image
This image shows the JWST data in five different wavelength NIRCam filters (top) for the gravitational lens and the lensed galaxy behind it together. At bottom, the light is broken up to display the foreground lens (left) and background ring (right) separated into their relevant components.
Credit: P. van Dokkum et al., Nature Astronomy accepted, 2023

Another 4 billion light-years behind the lens is a background galaxy, lensed perfectly into an Einstein ring.

jwst spitzer lensed galaxy
The same region of space that was imaged by JWST was previously imaged by Spitzer at long (24 micron) wavelengths. The difference in resolution between the two observatories, as well as the signal-to-noise discrepancies, show how superior JWST is to its infrared predecessor.
Credit: P. van Dokkum et al., Nature Astronomy accepted, 2023

The ring-shaped light reveals the lens’s mass: 650 billion Suns, concentrated within only a few thousand light-years.

Farthest gravitational lens observed old Hubble data
Once the most distant lensed galaxy was identified in JWST data, archival Hubble data was examined, where at 814 nanometers and 1.6 microns, evidence for the ring and the foreground lens were discovered in the data, respectively.
Credit: P. van Dokkum et al., Nature Astronomy accepted, 2023

Multiply imaged features within the ring may yet be resolved within the background galaxy.

two filter lens ring
By examining only a subset of the light from JWST, the ring can be separated from the foreground lens, where several key features (such as the red glow and bright star-forming regions) are highlighted and appear multiple times. With further analysis and future data, individual features in the background, lensed system may be more fully reconstructed.
Credit: P. van Dokkum et al., Nature Astronomy accepted, 2023

With lensing magnification and JWST’s capabilities combined, the Universe comes evermore into focus.

wide field cosmos-web lensed system
This wide-field view, centered on the most distant gravitational lens ever discovered, shows a larger area of the COSMOS-Web field. The Einstein ring is clear evidence of a gravitational lens.
Credit: P. van Dokkum et al., Nature Astronomy accepted, 2023

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.


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