Secrets of the universe: Scientists in South Dakota may have found dark matter
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C.J. Keene | South Dakota Public Broadcasting
In the 1930s, astronomer Fritz Zwicky hypothesized the existence of dark matter, a theoretical substance that physicists believe accounts for 85 percent of all matter in the universe but has never been detected.
Nearly a century later, scientists at the Sanford Underground Research Facility in South Dakota’s Black Hills, may have just proven Zwicky right. They believe they’ve detected dark matter at their Lux Zeplin experiment site in an old gold mine nearly a mile underground.
If confirmed, it would be a world-class scientific discovery and shake the field of particle physics, although Sanford researchers aren’t quite ready to pour out the good Scotch. Instead, they’re now poring through massive amounts of data to make sure they’re absolutely sure they have what they think.
“What haven’t we thought of? What could this be that isn’t dark matter?” Jaret Heise, director of science at the underground lab, asked aloud.
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Researchers, he said, will spend the next few months “scrutinizing the data, wracking their brains for every possible avenue that might confuse this signal as a more vanilla type of event as opposed to a fabulous new type of particle interaction that no one has ever seen before.”
Searching for WIMPs
Dark matter is called “dark” because it is invisible. NASA describes it as “the invisible glue that holds the universe together” and “shapes the cosmos, organizing galaxies and cosmic objects on a large scale.”
Theorizing about its existence is one thing. Proving it is another.
Scientists in Minnesota seemed close to cracking the code in the early 2000s. The Soudan Underground Laboratory, a half-mile below the Iron Range town of Soudan, was a hot spot for dark matter research. In 2009, scientists came close to announcing the discovery of dark matter on Earth. Six months later, the lab announced it was leaving Minnesota for a much deeper site in Canada.
Like the Minnesota project, scientists at the South Dakota site have been searching for weakly interacting massive particles, or WIMPs. These subatomic particles are seen as candidates for dark matter.
Finding these WIMPs or dark matter signatures is no simple feat. It’s less like finding a needle in a haystack and more like finding a specific grain of sand on a beach.
“A dark matter particle hitting an atom doesn’t give off a lot of energy, but the LZ experiment and other dark matter experiments using Xenon — others using argon — are really chasing this mysterious particle, looking for these very, very faint signatures that would indicate the existence of a dark matter particle,” Heise said.
Xenon and argon, noble gasses from the periodic table, are ultradense in liquid form. When something as small as a WIMP hits their atomic core it creates tiny flashes of light.
To be able to detect these tiny flashes, scientists set up their equipment deep in the Black Hills mineshaft.
‘Path of light’
Trying to prove dark matter exists remains the elusive prize. It interacts very weakly with ordinary matter.
It does exert a gravitational attraction and the effects can be seen among galaxy clusters, they’re “almost impossible to detect close-up. It’d be like trying to measure how the mass of the Eiffel Tower is pulling you towards it when you’re standing next to it. (It is, but very weakly),” according to the University of Chicago.
“Looking out at our solar system and into our universe and trying to understand how stars are rotating, how light is bending around objects we can’t see led to the hypothesis that there must be some matter out there that doesn’t emit light, but is, nonetheless, effecting the rotations and speeds of galaxies, and the path of light,” Heise said.
The Sanford Underground Research Facility findings are being submitted for peer review by collaborative scientists worldwide. They could mean a serious breakthrough if the data confirm this particle interaction as dark matter.
Meanwhile, the work continues.
Heise said there’s only one way to go from believing this could be dark matter, to being the first on Earth to know they’ve seen it with their own eyes. “More data.”
This story comes from the Upper Midwest Newsroom, a public media collaboration between Wisconsin Public Radio, South Dakota Public Broadcasting, Prairie Public in North Dakota and Minnesota Public Radio News made possible by the Corporation for Public Broadcasting.
