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Scientists used the Atacama Cosmology Telescope to create this new map of dark matter. The orange areas show where there is more mass; purple where there is less or none. The typical features are hundreds of millions of light years in diameter. The whitish band shows where contaminating light from dust in our Milky Way galaxy, as measured by the Planck satellite, obscures a deeper view. The new map uses light from the cosmic microwave background (CMB) mainly as a backlight to silhouette everything between us and the Big Bang. “It’s a bit like silhouetteing, but instead of just having black in the silhouette, you have texture and lumps of dark matter, as if the light was streaming through a fabric curtain that had lots of knots and bumps in it,” said Suzanne Staggs, director of ACT and Princeton’s Henry DeWolf Smyth Professor of Physics. “The famous blue and yellow CMB image is a snapshot of what the universe looked like during a single epoch, about 13 billion years ago, and now this gives us information about all the epochs since then.” Credit: ACT Collaboration
For millennia, people have been fascinated by the mysteries of the cosmos.
Unlike ancient philosophers who envision the origin of the universe, modern cosmologists use quantitative tools to gain insights into the evolution and structure of the universe. Modern cosmology dates back to the early 20th century, with the development of Albert Einstein’s general theory of relativity.
Now, scientists from the Atacama Cosmology Telescope (ACT) collaboration have created a groundbreaking new image that reveals the most detailed map of dark matter distributed across a quarter of the entire sky and extending deep into the cosmos. In addition, it confirms Einstein’s theory of how massive structures grow and bend light, over the entire 14 billion year lifetime of the universe.
“We have mapped the invisible dark matter across the sky to the greatest distances, and clearly see features of this invisible world hundreds of millions of light-years across,” says Blake Sherwin, professor of cosmology at the University of Cambridge, where he leads a group of ACT- researcher. “It looks exactly as our theories predict.”
The Atacama Cosmology Telescope in northern Chile, supported by the National Science Foundation, operated from 2007–2022. The project is led by Princeton University and the University of Pennsylvania—Director Suzanne Staggs at Princeton, Associate Director Mark Devlin at Penn—with 160 collaborators at 47 institutions. Credit: Mark Devlin, associate director of the Atacama Cosmology Telescope and Reese Flower Professor of Astronomy at the University of Pennsylvania
Despite making up 85% of the universe and influencing its evolution, dark matter has been difficult to detect because it does not interact with light or other forms of electromagnetic radiation. As far as we know, dark matter only interacts with gravity.
To track it, the more than 160 collaborators who have built and collected data from the National Science Foundation’s Atacama Cosmology Telescope in the high Chilean Andes are observing light emitted after the dawn of the universe’s formation, the Big Bang—when the universe was only 380,000 years old . Cosmologists often refer to this diffuse light that fills our entire universe as the “baby picture of the universe,” but formally it is known as cosmic microwave background radiation (CMB).
The team tracks how attraction of large, heavy structures including dark matter distorts the CMB on its 14-billion-year journey to us, like the way a magnifying glass bends light as it passes through its lens.
“We’ve made a new mass map of the distortions of light left over from the Big Bang,” said Mathew Madhavacheril, assistant professor in the Department of Physics and Astronomy at the University of Pennsylvania. “Remarkably, it provides measurements showing that both the ‘lumpiness’ of the universe and the rate at which it is growing after 14 billion years of evolution are exactly what you would expect from our standard model of cosmology based on Einstein’s theory of gravity.”
Research from the Atacama Cosmology Telescope collaboration has culminated in a ground-breaking new map of dark matter distributed over a quarter of the entire sky, reaching deep into the cosmos. The findings provide further support for Einstein’s theory of general relativity, which has been the basis of the Standard Model of cosmology for more than a century, and offer new methods for demystifying dark matter. Credit: Debra Kellner
Sherwin adds, “our results also provide new insights into an ongoing debate that some have called ‘The Crisis in Cosmology,'” explaining that this crisis stems from recent measurements that use a different background light, one emitted from stars in galaxies rather than CMB.. These have produced results that suggest dark matter was not clumsy enough under the Standard Model of Cosmology and led to concerns that the model may be broken. However, the team’s latest results from ACT were able to accurately judge that the huge lumps seen in this image are exactly the right size.
“When I first saw them, our measurements agreed so well with the underlying theory that it took me a while to process the results,” said the 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.”
“CMB lensing data rival more conventional surveys of the visible light from galaxies in their ability to trace the sum total of what’s out there,” said Suzanne Staggs, director of ACT and Henry DeWolf Smyth Professor of Physics at Princeton University. “Together, the CMB lens and the best optical surveys clarify the evolution of all mass in the universe.”
“When we proposed this experiment in 2003, we had no idea of the full extent of information that could be extracted from our telescope,” said Mark Devlin, Reese Flower Professor of Astronomy at the University of Pennsylvania and deputy director of ACT. “We owe this to the skill 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.”
Research from the Atacama Cosmology Telescope collaboration has culminated in a ground-breaking new map of dark matter distributed over a quarter of the entire sky, reaching deep into the cosmos. The findings provide further support for Einstein’s theory of general relativity, which has been the basis of the Standard Model of cosmology for more than a century, and offer new methods for demystifying dark matter. Credit: Lucy Reading-Ikkanda, Simons Foundation
ACT, which operated for 15 years, was decommissioned in September 2022. Still, more papers presenting the results of the final set of observations are expected to be submitted soon, and the Simons Observatory will conduct future observations at the same site, with a new telescope scheduled to begin operation in 2024 .This new instrument will be able to map the sky almost 10 times faster than ACT.
This research will be presented at “Future science with CMB x LSS”, a conference running from April 10–14 at the Yukawa Institute for Theoretical Physics, Kyoto University.
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