First ‘Einstein Zig-Zag’ Found in Space May Help Solve Mystery of Space Expansion

A source of light in space that was believed to be the bending light of a galaxy from a distant galactic core is actually a rare and first-of-its-kind gravitational lens, according to the research team that studied the system.

The system is called J1721+8842, and it was first discovered in 2017. At the time, the system was thought to be a galaxy bending the light of a distant quasar—a powerful galactic nucleus. But after two years of observations with the Nordic Optical Telescope—and data from the James Webb Space Telescope—the latest team says the object is actually a composite lens, made up of two aligned galaxies. In addition, the team postulates that the light travels through the lens in a zig-zag pattern. The group’s research is currently hosted on the preprint server arXiv, and suggests that rare structures may help answer some important questions about the universe.

“In this book, we present evidence from light curves obtained from the Nordic Optical Telescope (NOT), new redshift measurements from the James Webb Space Telescope (JWST) Near InfraRed Spectrograph (NIRSpec), and revised lensing models, which unequivocally confirm the situation where one source is lensed in J1721+8842,” the team wrote.

Gravitational lenses are objects with significant gravitational fields that bend light from other sources in the universe. Gravitational lensing was proposed by Einstein as early as 1912.

Gravitational lenses are used by astronomers because they magnify distant light that would otherwise be too faint to be seen. In other words, gravitational lenses are the sites of the most distant and oldest parts of the universe; in 2022, astronomers used gravitational lensing to observe Eardel, the oldest known star.

Sometimes, gravitational lenses form rings of light in the sky, called Einstein rings. Last year, another group suggested that Einstein’s rings raised the axion charge in physics’ race to discover the events that cause dark matter, the 27% of the universe that we know is there but can’t directly see.

Earlier this year, a team at Lawrence Berkeley National Laboratory identified a very fine gravitational lens formed by the formation of galaxies that they say is the size of “eight perfectly placed needles” in a haystack. Inside that lens was an Einstein Cross, which showed an even distribution of mass (including black dye) throughout the lens.

Unlike previous gravitational lenses, however, the structure of J1721+8842 shows that the light in the lens fluctuates between the two galaxies; hence, the very first “Einstein zig-zag lens”.

“Full lensing models, time-delay measurements and cosmology constraints derived from this program will be published in follow-up papers as part of the TDCOSMO collaboration,” the researchers added. This means that the double lens system can help Hubble astronomers understand the constant, a number that describes the rate of expansion of the universe. The constant is different depending on how you calculate it, a problem known as the Hubble tension.

Being able to scan the composite lens for a new Hubble measurement every now and then will help astronomers understand whether the equation is consistent with the model of the universe or not. The team noted that the lens “can also measure the distances between the observer, the lens and the two sources, allowing an accurate measurement of the expansion history of the universe.”

Advanced telescopes are a modern marvel, and they can help answer some of humanity’s most important questions—where did everything come from, and where are we going, in the first place. But gravitational lenses make the work of telescopes easier, by allowing the laws of gravity to magnify some of the most distant regions of the universe. Aside from the details they can provide, the lenses deserve attention in their own right. J1721+8842 is Einstein’s zig-zag in space—I mean, that’s all sounds cool as hell.