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For millennia, humans have been fascinated by the mysteries of the cosmos.
Unlike ancient philosophers who imagined the origins of the universe, modern cosmologists use quantitative tools to better understand the evolution and structure of the universe. Modern cosmology dates back to the early 20th century, with the development of Albert Einstein’s theory of general relativity.
Today, researchers from the Atacama Cosmology Telescope (ACT) collaboration have created a groundbreaking new image that reveals the most detailed map of dark matter spread across a quarter of the sky, reaching deep into the cosmos. Moreover, it confirms Einstein’s theory of how massive structures grow and bend light, over the entire 14 billion year lifespan of the universe.
“We’ve mapped invisible dark matter across the sky to the greatest distances, and clearly see features of this invisible world that span hundreds of millions of light-years,” says Blake Sherwin, professor of cosmology at the University of Cambridge, where he leads a group of ACT researchers. “It looks like what our theories predict.”
Although it represents 85% of the universe and influences its evolution, dark matter is difficult to detect because it does not interact with light or other forms of electromagnetic radiation. To our knowledge, dark matter only interacts with gravity.
To find it, the more than 160 collaborators who built and collected data from the National Science Foundation’s Atacama Cosmology Telescope in the high Chilean Andes observe the light emanating 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 (CMB) radiation.
The team is tracking how the gravitational pull of large heavy structures, including dark matter, warps the CMB on its 14 billion year journey towards us, like how a magnifying glass bends light as it passes through through his lens.
“We created a new mass map using the distortions of light left behind by the Big Bang,” says Mathew Madhavacheril, assistant professor in the Department of Physics and Astronomy at the University of Pennsylvania. “Remarkably, it provides measurements that show that the ‘fatness’ of the universe, and the rate at which it is expanding after 14 billion years of evolution, is exactly what you would expect from our standard model of cosmology based on Einstein’s theory. gravity.”
Sherwin adds, “Our results also provide new insights into an ongoing debate that some have called ‘the crisis of cosmology'”, explaining that this crisis stems from recent measurements that use a different background light, that emitted by stars. galaxies rather than the CMB. These produced results suggesting that dark matter was not lumpy enough in the standard model of cosmology and led to fears that the model might be broken. However, the latest results from the ACT team have accurately assessed that the vast masses 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,” says Cambridge Ph.D. student Frank Qu. , member of the research team. “It will be interesting to see how this possible discrepancy between the different measures will be resolved.”
“CMB lens data rivals more conventional surveys of the visible light of galaxies in their ability to plot the sum of what exists,” says ACT Director Suzanne Staggs and Henry DeWolf Smyth Professor of Physics at the 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 scope of information that could be extracted from our telescope,” says Mark Devlin, Reese Flower Professor of Astronomy at the University of Pennsylvania and Deputy Director of the ACT. “We owe it to the ingenuity of theorists, the many people who built new instruments to make our telescope more sensitive, and the new analysis techniques our team developed.”
ACT, which operated for 15 years, was decommissioned in September 2022. Nevertheless, further papers presenting the results of the final set of observations are expected to be submitted soon, and the Simons Observatory will perform future observations on the same site, with a new telescope. should enter service 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 taking place April 10-14 at Kyoto University’s Yukawa Institute for Theoretical Physics.
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