On November 17, 2024, a team of international astronomers announced the discovery of an Einstein zig-zag lens, marking a significant milestone in astronomical research. The findings, published on the pre-print archive arXiv, detail the sighting of two galaxies that align in such a manner that their combined gravitational effects act as a compound lens.
Previous studies had identified instances of galaxies bending light in accordance with Einstein's theory of general relativity, but this configuration is deemed extremely rare. The researchers noted that two out of six multiple images are deflected in opposing directions as they pass the first lens galaxy on one side and the second on the other, creating zig-zag optical paths.
The system, designated J1721+8842, was initially thought to involve a single elliptical galaxy bending light from a quasar. However, a two-year analysis revealed variations in the quasar's image and small light spots that appeared to be duplicates from one source.
This unique setup enabled the application of time-delay cosmography and dual source-plane lensing techniques. Further investigation confirmed that the six light spots matched the main quartet, indicating they originated from the same source. Data from the James Webb Space Telescope helped clarify that what was initially perceived as an Einstein ring was actually a second lensing galaxy.
The astronomers created a computer model to validate their observations as a compound lens. This discovery is expected to enhance calculations of the Hubble constant, potentially addressing ongoing debates regarding its true value. According to cosmologist Thomas Collett from the University of Portsmouth, these lensed quasars could provide critical insights into whether the universe's expansion rate corresponds with the cosmological model.
However, Collett cautioned that deriving accurate calculations will be complex and may take over a year to complete as the team works to analyze the intricate images of J1721+8842.