Webb Space Telescope Locates First ‘Einstein Zig-Zag’

Nov. 22 () –

Using the James Webb Space Telescope (JWST), astronomers have discovered the first “Einstein zig-zag,” an image of a quasar repeated six times in a single image.

This system, designated J1721+8842, is composed of a quasar, which is an extremely luminous galactic nucleus, surrounded by two very separated but perfectly aligned galaxies. Not only is this sighting incredibly rare, marking a fascinating example of a curious space-time curvature phenomenon introduced in Albert Einstein’s theory of gravity, general relativity, but zig-zag J1721+8842 also has a power that standard gravitational lenses do not have.

“I am excited, not only because this is a fascinating natural phenomenon, but also because this system is incredibly promising for measuring cosmological parameters,” told Space.com Martin Millon, a member of the discovery team and a cosmologist at Stanford University. “This lens system offers the potential to impose tight constraints on both the Hubble constant and the dark energy equation of state, something that is not generally possible,” he added. The findings are published in arXiv.

General relativity states that objects with mass cause a curvature in the very fabric of space and time, united as a single entity called “spacetime.” The greater the mass of an object, the greater the “dent” it makes in space-time. Since gravity arises from this curvature, the more mass an object has, the greater its gravitational influence.

Gravitational lensing occurs when light from a background source passes in front of a large body on its way to Earth and therefore follows the resulting curvature in space, causing its own road curves. Light from this background source takes different paths around a gravitational lens, approaching the lens mass at different distances and bending by different amounts. This means that this light from the same background source can reach the same telescope at different times.

As a result, a single backlight-emitting body can appear in multiple locations in a single image. These objects can form arrangements such as Einstein rings, Einstein crosses, and, in this currently unique case, an Einstein zigzag.

JWST was not actually the first telescope to detect J1721+8842. The lensing quasar, which is more specifically composed of glowing gas and dust around a feeding supermassive black hole, was discovered by Cameron Lemon in 2017 using the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) located at the Haleakala Observatory in Hawaii.

At first, the quasar appeared to be surrounded by only a four-fold lens. However, the sensitivity of the JWST has revealed that two galaxies are actually lensing this distant quasar six times, and that the most distant galaxy in this arrangement is also being lensed by the nearest galaxy.

“Normally, gravitational lenses created by a single galaxy form two or four images of the background source, depending on the alignment. In this case, there is an exceptional alignment between two galaxies and a background quasar, forming a rare configuration of six images. We call it ‘Einstein’s zigzag’ because the optical path of two of the multiple images passes by the first galaxy on one side before being deflected by the second galaxy on the other side.. “This optical path creates a zigzag pattern between the two galaxies,” Millon explained.

Lead author of the research and EPFL Astrophysics Laboratory scientist Frédéric Dux told Space.com that this is the first time scientists have found such a perfect alignment between three different bodies that they create a gravitational lens.

“Normally, a gravitational lens would involve just two objects, say a galaxy acting as a lens and another galaxy behind it, acting as a source, whose light is deflected by the one in the foreground,” Dux said. “Of course, there are many cases of lensing that occur due to multiple galaxies at once, such as in the lensing of galaxy clusters. In those cases, the effects of the different deflectors combine in a weak way. You wouldn’t find a single galaxy that acts as a perfect lens on its own. The lineup just isn’t good enough.”