The Atacama Cosmology Telescope collaboration has made a significant breakthrough in uncovering the universe’s evolution. Researchers have produced an image that illustrates the most precise map of dark matter distributed throughout a quarter of the sky, extending into the cosmos’s depths.

The image verifies Einstein’s theory of how massive structures expand and distort light over the universe’s 14-billion-year existence.

“We have mapped the invisible dark matter across the sky to the largest distances, and clearly see features of this invisible world that are hundreds of millions of light-years across,” adds Blake Sherwin, professor of cosmology at the University of Cambridge. “It looks just as our theories predict.”

Dark matter constitutes 85% of the universe and significantly influences its evolution; however, detecting it has been challenging because it does not interact with light or other types of electromagnetic radiation, and as far as we know, it only interacts with gravity.

To track down dark matter, over 160 researchers who have constructed and gathered data from the National Science Foundation’s Atacama Cosmology Telescope in the Chilean Andes scrutinize the light that emerged after the universe’s inception, specifically during the Big Bang, when the universe was a mere 380,000 years old.

Cosmologists often refer to this light, which fills the universe, as the “baby picture of the universe.” It is also formally known as cosmic microwave background radiation (CMB).

The researchers track how the gravitational force of massive, weighty structures, including dark matter, alters the CMB during its 14-billion-year voyage to us. It is comparable to how a magnifying glass distorts light as it passes through its lens.

“We’ve made a new mass map using distortions of light left over from the Big Bang,” explains Mathew Madhavacheril, assistant professor in the Department of Physics and Astronomy at the University of Pennsylvania. “Remarkably, it provides measurements that show that both the ‘lumpiness’ of the universe and the rate at which it is growing after 14 billion years of evolution, are just what you’d expect from our standard model of cosmology based on Einstein’s theory of gravity.”

Sherwin notes that their findings provide fresh perspectives on an ongoing dispute known as the “Crisis in Cosmology.” This predicament arises from recent measurements that employ a distinct background light emitted by stars in “galaxies rather than the CMB.” These measurements have yielded outcomes that imply that the dark matter was not clumpy enough under the typical model of cosmology, raising concerns that the model might be flawed. Nevertheless, the team’s latest outcomes from ACT effectively confirm that the enormous clumps observed in the image are precisely the correct size.

“When I first saw them, our measurements were in such good agreement with the underlying theory that it took me a moment to process the results,” adds Cambridge Ph.D. student Frank Qu, part of the research team. “It will be interesting to see how this possible discrepancy between different measurements will be resolved.”

“The CMB lensing data rivals more conventional surveys of the visible light from galaxies in their ability to trace the sum of what is out there,” adds Suzanne Staggs, director of ACT and Henry DeWolf Smyth Professor of Physics at Princeton University. “Together, the CMB lensing and the best optical surveys are clarifying the evolution of all the mass in the universe.”

“When we proposed this experiment in 2003, we had no idea the full extent of information that could be extracted from our telescope,” says Mark Devlin, the Reese Flower Professor of Astronomy at the University of Pennsylvania and the deputy director of ACT. “We owe this to the cleverness of the theorists, the many people who built new instruments to make our telescope more sensitive, and the new analysis techniques our team came up with.”

ACT, which functioned for 15 years, was retired in September 2022. However, more publications disclosing findings from the ultimate set of observations are anticipated to be submitted shortly.

The Simons Observatory is set to undertake future observations at the same location, and a new telescope is planned to commence operations in 2024. This cutting-edge device will be able to map the sky approximately ten times faster than ACT.

Image Credit: Lucy Reading-Ikkanda, Simons Foundation