March 1, 2024

Results emerge from the new South Pole Telescope camera

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Cosmic microwave background radiation – the oldest light in the universe – traversed vast distances before reaching us. During its long journey, the gravitational forces of massive cosmic structures caused its trajectory to curve before it was captured by the South Pole Telescope. Credit: Zhaodi Pan/Argonne National Laboratory

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Cosmic microwave background radiation – the oldest light in the universe – traversed vast distances before reaching us. During its long journey, the gravitational forces of massive cosmic structures caused its trajectory to curve before it was captured by the South Pole Telescope. Credit: Zhaodi Pan/Argonne National Laboratory

For more than five years, scientists at the South Pole Telescope in Antarctica have been observing the sky with an updated camera. The gaze extended toward the cosmos is capturing light reminiscent of the early formation of the universe. Now researchers have analyzed an initial batch of data, publishing details in the journal Physical Review D. The results from this limited dataset suggest even more powerful future insights into the nature of our universe.

The Amundsen-Scott South Pole Station telescope, operated by the National Science Foundation, received a new camera known as SPT-3G in 2017. Equipped with 16,000 detectors – 10 times more than its predecessor – SPT-3G is central to multi-institutional research led in part by the U.S. Department of Energy’s (DOE) Argonne National Laboratory. The goal is to measure the faint light known as the cosmic microwave background (CMB). The CMB is the afterglow of the Big Bang, when the Universe emerged from a single point of energy almost 14 billion years ago.

“The CMB is a treasure map for cosmologists,” said Zhaodi Pan, lead author of the paper and Maria Goeppert Mayer Fellow at Argonne. “Their tiny variations in temperature and polarization provide a unique window into the universe’s infancy.”

The role in Physical Review D offers the first CMB gravitational lensing measurements from SPT-3G. Gravitational lensing happens when the universe’s vast web of matter distorts the CMB as it travels through space. If you were to place the curved base of a wine glass on the page of a book, the glass would distort your view of the words behind it. Likewise, matter in the telescope’s line of sight forms a lens that deflects the CMB light and our view of it. Albert Einstein described this deformation in the structure of spacetime in his theory of general relativity.

Measurements of this distortion hold clues about the early universe and mysteries like dark matter, an invisible component of the cosmos. “Dark matter is difficult to detect because it does not interact with light or other forms of electromagnetic radiation. Currently, we can only observe it through gravitational interactions,” said Pan.

Scientists have been studying the CMB since it was discovered in the 1960s, observing it through telescopes both on the ground and in space. Although the latest analysis uses just a few months of SPT-3G data from 2018, measuring gravitational lensing is already competitive in the field.

“One of the really interesting parts of this study is that the result comes from what is essentially the commissioning of data from when we were just beginning observations with SPT-3G – and the result is already great,” said Amy Bender, an Argonne physicist and co-author of the article. “We have another five years of data that we’re working on analyzing now, so this just hints at what’s to come.”


In this scaled matter distribution for all matter in the observable universe, measured by SPT-3G, red indicates areas of higher matter density, while blue indicates lower density. Credit: Physical Review D (2023). DOI: 10.1103/PhysRevD.108.122005

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In this scaled matter distribution for all matter in the observable universe, measured by SPT-3G, red indicates areas of higher matter density, while blue indicates lower density. Credit: Physical Review D (2023). DOI: 10.1103/PhysRevD.108.122005

The dry, stable atmosphere and remote location of the South Pole Telescope create as little interference as possible when looking for CMB patterns. Still, data from the highly sensitive SPT-3G camera contains contamination from the atmosphere as well as from our own galaxy and extragalactic sources.

Analyzing even a few months of SPT-3G data is a years-long task, as researchers need to validate data, filter noise, and interpret measurements. The team used a dedicated cluster, a group of computers, at the Argonne Laboratory Computing Resource Center to perform some of the research’s calculations.

“We found that the lensing patterns observed in this study are well explained by general relativity,” said Pan. “This suggests that our current understanding of gravity is valid at these large scales. The results also strengthen our existing understanding of how structures of matter were formed in our Universe.”

SPT-3G lens maps from additional years of data will also help probe cosmic inflation, or the idea that the early universe underwent rapid exponential expansion. Cosmic inflation is “another cornerstone of cosmology,” Pan noted, and scientists are looking for signs of early gravitational waves and other direct evidence of this theory. The presence of gravitational lenses introduces interference with inflationary impressions, necessitating the removal of this contamination, which can be calculated through precise lens measurements.

While some results from the new SPT-3G data reinforce existing knowledge, others will raise new questions.

“Every time we add more data, we find more things we don’t understand,” said Bender, who has a joint appointment at the University of Chicago. “As you peel back layers of this onion, you learn more and more about your instrument and also about your scientific measurement of the sky.”

So little is known about the invisible components of the universe that any understanding gained is critical, Pan said: “The more we learn about the distribution of dark matter, the closer we come to understanding its nature and its role in shaping the universe in which we live. . today.”

More information:
Z. Pan et al, Measurement of gravitational lensing of the cosmic microwave background using SPT-3G 2018 data, Physical Review D (2023). DOI: 10.1103/PhysRevD.108.122005

Diary information:
Physical Review D

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