In the never-ending search to accurately describe the universe, new generations of scientists are adapting decades-old technology to make new discoveries.
Sometimes those techniques don’t find what they’re looking for, but still result in more knowledge and new approaches, as researchers in Ohio State University’s astronomy and physics department have found in their search for dark matter using radar.
Like many scientific discoveries, radar was finetuned as a tool for war, becoming an important part of World War II after is discovery decades earlier.
Now it's used for everything from navigation to weather forecasting.
And Ohio State University researchers have found yet another use. In a recent paper, three researchers working under physics and astronomy professor John Beacom outlined a new technique to search for dark matter.
Their initial approach used data generated by radar technology set up to detect meteorites entering the atmosphere at observatories in Japan and Antarctica.
When something like a meteor enters the atmosphere, observatories can use radar to find the particles they leave behind. The larger ones create shooting stars, while the smaller ones will leave a trace that can still be detected.
“If you look up at the sky, you don't see anything. But a big cloud of electrons will reflect radio waves. So, if we send radar signals from the ground, it will go up there and it'll bounce off of those electrons just like it's like a little piece of metal in the sky," Beacom said.
The team theorized that if dark matter particles are large enough, and interact with regular matter enough, they might show up in the data.
“Dark matter makes up about 85% of the matter in the universe," said Chris Cappiello, who was a PhD student who worked on the paper with Beacom, along with Pawan Dhakal and Steven Prohira. “But we don't know what it is, to be rather blunt about it," Cappiello said.
Beacom said dark matter is just the name of the concept describing matter that hasn’t yet been accounted for in the universe.
“We don't know if it's really massive particles, and there's not that many of them, or little, low mass particles, and there's a lot of them. We know how much total mass there is, but we don’t know the identity of the particles,” Beacom said.
But we know there’s some massive amount of matter out there that hasn’t been accounted for yet, because of the way galaxies and stars are moving through space.
“And all of this evidence is pointing to the idea that most of the mass in galaxies, in fact, most of the mass in the universe, is something that we cannot see. It's not just the stars and gas and things that we're able to see with a telescope,” Cappiello said.
Beacom said to understand where our understanding of dark matter lies today, think about the way humanity first started to understand germ theory.
“For a long time, people knew that something made people sick. But they didn't know what it was. And they had all kinds of crazy theories, and you know, about vapors and cold weather and hexes," Beacom said.
Over time, people came to understand the idea that “germs” were being passed from one person to another, though they couldn’t see the organisms to study them, he said.
“They started to have a name or a concept, but they didn't actually know what it was. And that's sort of like where we are with dark matter. We know it’s a thing,” Beacom said, we just haven't been able to observe it, yet.
This experiment looked for large, highly interacting particles.
“We did not discover dark matter," Cappiello said.
But, the research still added to the knowledge of what dark matter doesn’t do.
“We are able to say, if dark matter existed anywhere in this parameter space, we would have seen it, but we did not," he said.
And, Beacom said the approach to using radar can be adapted to search for particles of other masses and levels of interaction.
“This whole approach could be greatly improved. These radar data that we used are intended to find these little, teeny tiny meteors,” Beacom said.
Cappiello remains fascinated by the unknown and is continuing his studies on dark matter as a postdoctoral fellow at Queen’s University in Ontario.
“If you discover dark matter, you win the Nobel Prize,” Cappiello said.
Scott Palo and John Marino with the University of Colorado also assisted with their work at the observatory in Antarctica.
