MOTHRA: World’s Largest Lens Telescope Hunts for Dark Matter & Cosmic Web

The search for dark matter just got a massive upgrade – literally. Astronomers are building MOTHRA (Massive Optical Telephoto Hyperspectral Robotic Array), a telescope unlike any other, in the Chilean Andes. Instead of a single, enormous mirror, MOTHRA will employ 1,140 Canon EF 400mm f/2.8L IS telephoto lenses to map the distribution of faint ionized gas, hoping to reveal the structure of the universe’s elusive dark matter.

The project, underway at the Obstech/El Sauce Observatory in Chile’s Rio Hurtado Valley, builds on earlier work with a smaller lens array called Dragonfly. While Dragonfly focused on the dim light of distant stars and galaxies, MOTHRA’s sheer scale – equivalent to a 4.7-meter lens – will allow it to detect far more subtle signals. Construction began in January, and the team anticipates full operation by the finish of 2026. DPReview and Yahoo News both reported on the project this week.

From Insect Eyes to Cosmic Webs

The name “MOTHRA” isn’t arbitrary. Researchers Pieter van Dokkum of Yale University and Roberto Abraham of the University of Toronto, the project’s co-founders, drew inspiration from the compound eyes of insects. These eyes, composed of numerous individual lenses, maximize light capture and provide a wide field of view. “It sprang from a sincere desire to do science in a faster and better way,” Abraham explained in an interview with The Globe and Mail. The telescope’s design reflects this biological model, stitching together the views from each of its 1,140 lenses.

But MOTHRA isn’t just about mimicking nature. It’s about tackling a fundamental question in cosmology: what is dark matter, and how is it distributed throughout the universe? Dark matter, which makes up roughly 85% of the matter in the universe, doesn’t interact with light, making it invisible to traditional telescopes. But, astronomers believe it exerts a gravitational influence on visible matter, shaping the large-scale structure of the cosmos. This structure is thought to resemble a vast cosmic web, with galaxies clustered along filaments of dark matter.

How MOTHRA Sees the Invisible

MOTHRA’s approach isn’t to directly detect dark matter particles (a goal pursued by other experiments), but to map the distribution of ionized gas that permeates the space between galaxies. This gas is thought to be influenced by the gravitational pull of dark matter, effectively tracing the underlying structure of the cosmic web.

Each of MOTHRA’s lenses is paired with either an Atik Cameras Apx26 or Apx60 camera, utilizing Sony IMX571 and IMX455 BSI CMOS sensors – 26-megapixel and 60-megapixel chips commonly found in consumer cameras from brands like Fujifilm, Sony, and Leica. The team specifically chose Canon’s EF lenses, rather than the newer RF mount, due to the EF mount’s greater back focus distance, which allows for the attachment of necessary accessories. The entire system is controlled by a network of Raspberry Pi 4B computers – 90 of them dedicated to guiding the array, with one Pi managing each camera.

Building on Dragonfly: A History of Lens Arrays

MOTHRA isn’t the first time van Dokkum and Abraham have experimented with using arrays of lenses as telescopes. The Dragonfly Telephoto Array, commissioned in 2013, started with just three lenses and gradually expanded to 24, then 48. PetaPixel covered the Dragonfly project in 2021, detailing its evolution. Dragonfly used CCD sensors, while MOTHRA utilizes the more modern CMOS technology. The success of Dragonfly demonstrated the feasibility of this unconventional approach, paving the way for the much larger and more ambitious MOTHRA project.

The leap from 48 lenses to 1,140 represents a significant increase in light-gathering power and sensitivity. Van Dokkum estimates that MOTHRA will require roughly ten times more lenses than Dragonfly to observe the faint ionized gas they’re targeting. “We have over a decade of experience with this family of lenses and continue to be delighted with both the quality of the lenses and the quality of support we have received from both Canon Japan and Canon USA,” the team stated.

Implications and Limitations

If successful, MOTHRA could revolutionize our understanding of dark matter and the cosmic web. Currently, simulations provide our best models of these structures, but direct observational evidence is scarce. MOTHRA’s observations could provide crucial data to test and refine these models, potentially revealing recent insights into the nature of dark matter and the evolution of the universe.

However, it’s essential to acknowledge the limitations of this approach. The data collected by MOTHRA will require sophisticated processing to account for the distortions and imperfections inherent in using so many individual lenses. The telescope’s resolution will be limited by the size of its effective aperture (4.7 meters), meaning it won’t be able to resolve fine details in the same way as larger, traditional telescopes. The project also relies heavily on the consistent performance of a large number of individual components – lenses, cameras, and computers – increasing the potential for systematic errors.

What’s Next for MOTHRA?

With construction well underway and expected to be completed by the end of 2026, the next phase for MOTHRA involves rigorous testing and calibration. The team will need to carefully characterize the performance of each lens and camera, and develop algorithms to combine the data from all 1,140 sources into a coherent image. Initial observations have already yielded promising results, including images of the Sculptor Galaxy (NGC 253) and the Dragon’s Heart Nebula (RCW 114). The team will then begin a systematic survey of the sky, mapping the distribution of ionized gas and searching for evidence of the cosmic web. The data will be made available to the broader astronomical community, fostering further research and collaboration.