A key realization of Einstein’s theory of general relativity is the fact that massive objects distort space-time in a manner similar to a lens, magnifying and shifting light from background objects. This was a crucial test for the theory of relativity just four years after it was proposed, and has been seen in countless examples. Today, 105 years after the first test, astronomers continue to discover never-before-seen alignments. Meet the zigzag lens.
All gravitational lenses are exciting, but some are more exciting than others. At first glance, J1721+8842 was intriguing, but not particularly revolutionary. In this system, light from a distant quasar has traveled more than 10.5 billion years to reach us. After passing through a lens, it formed six visible images. The number six was unique, which made it interesting, the authors of the paper (which has yet to be finalized by peer review) explain. In recent years there was a proposal to be able to form six images under certain conditions, that is, with two lenses.
The first lens is relatively close to the source, with an estimated distance of 10.2 billion light-years. What happens is that the light from the quasar is magnified and multiplied throughout this enormous galaxy. Two of the images are deflected in the opposite direction when they reach the second lens, another massive galaxy. The path of the light is a zigzagging motion between the quasar, the first lens and then the second, which is only 2.3 billion light years away.
Not only that, but the second lens also magnifies the first – although not very bright, this can be seen in the images collected by JWST. The team believes this is the first case of a double gravitational lens and the first example of a strong galaxy-scale gravitational lens with six images of the same distant object.
This is an accidental and extraordinary find. The researchers were curious about the odds of finding such a precise alignment between us, two lenses and a quasar on a single line of sight spanning 10.5 billion light-years. They estimate this to be one in 100 million.
If this isn’t enough, this object seems like a cornucopia of excitement. It is the northernmost gravitational lens known, meaning there are many ground-based telescopes that can make follow-up observations. Its special nature could also be used to better estimate the expansion rate of the universe – a current topic of heated debate in cosmology.
The paper is currently awaiting peer review by Astronomy & Astrophysics and is currently available on the ArXiv.