What is Dark Matter? We don’t know. At this stage of the game, scientists are busy trying to detect it and map out its presence and distribution throughout the Universe. Usually, that involves highly-engineered, sophisticated telescopes.
But a new approach involves a device so small it can sit on a kitchen table.
A collaboration between the University of Chicago and the Fermi National Accelerator Laboratory has resulted in a tabletop device called Broadband Reflector Experiment for Axion Detection or BREAD. BREAD is built to detect dark matter, and its first results are now available in a new paper.
The paper is “First Results from a Broadband Search for Dark Photon Dark Matter in the 44 to 52 µeV Range with a Coaxial Dish Antenna.” It’s published in Physical Review Letters, and the lead author is Stefan Knirck. Knirck is a Fermilab postdoctoral scholar who led the construction of the detector.
The word ‘mysterious’ barely describes dark matter. It constitutes about 85% of the matter in the Universe. It can’t be seen, but its presence is inferred from observations. Its mass holds galaxies together; without it, they would fly apart.
“We’re very confident that something is there, but there are many, many forms it could take.”
David Miller, University of Chicago
Dark matter is sometimes described as the Universe’s backbone or the scaffolding that holds regular matter. Simulations like TNG Illustris showed how dark matter is distributed throughout the Universe in a network of filaments and clumps. The distribution of galaxy clusters follows the same pattern.
Physicists still don’t know what dark matter is. But it’s there, and there are several candidates.
“We’re very confident that something is there, but there are many, many forms it could take,” said University of Chicago Associate Professor David Miller. Miller is a co-leader of the BREAD experiment.
One of the candidates is a hypothetical type of particle called an axion. If they’re real and their mass is within certain limits, they could be one of dark matter’s components.
The BREAD experiment focuses on the mass range of 10.7–12.5 GHz. Within that range, it searches for dark photon dark matter. Along with axions, they’re one of the most promising candidates for dark matter. Dark photons are a hypothetical type of particle that physicists think might act as a force carrier for dark matter like photons are force carriers for electromagnetism. Axions and dark photons are linked in the search for dark matter, but a detailed explanation is beyond the scope of this article. (Watch Fraser Cain’s videos for a deeper dive.)
BREAD’s first run lasted 24 days and didn’t detect anything; if it had, it would be huge news, and we’d all hear it. But, since its effort is so focused, the lack of detection is still constructive.
“We’re very excited about what we’ve been able to do so far,” said Miller, “There are lots of practical advantages to this design, and we’ve already shown the best sensitivity to date in this 11-12 gigahertz frequency.”
Each candidate for dark matter requires a specific search. Physicists build detectors aimed at specific candidates. BREAD is a little bit different. As its name illustrates, it’s a broadband detector. It can search across a range of frequencies, though its precision suffers.
“If you think about it like a radio, the search for dark matter is like tuning the dial to search for one particular radio station, except there are a million frequencies to check through,” said Miller. “Our method is like doing a scan of 100,000 radio stations, rather than a few very thoroughly.”
This version of BREAD is a scaled-down version of what the full-scale version will be. Eventually, BREAD will sit inside a magnet. The magnetic field will boost the chances that dark matter particles will be converted into detectable photons. This first 24-day run was a proof of principle.
“This is just the first step in a series of exciting experiments we are planning.”
Andrew Sonnenschein, Fermilab
Though this first proof of principle run didn’t detect any dark matter, the results were still helpful. The run showed that BREAD is very sensitive in its frequency range. The researchers think they can improve the sensitivity even more.
“This is just the first step in a series of exciting experiments we are planning,” said Andrew Sonnenschein from Fermilab, who originally developed the concept behind BREAD. “We have many ideas for improving the sensitivity of our axion search.”
Dark matter and what comprises it is one of the most confounding questions in science. For Miller, BREAD is more than just another science experiment. It speaks to the creativity needed to explore dark matter thoroughly and the way researchers at different institutions can work together to make progress.
“There are still so many open questions in science and an enormous space for creative new ideas for tackling those questions,” said Miller. “I think this is really a hallmark example of those kinds of creative ideas—in this case, impactful, collaborative partnerships between smaller-scale science at universities and larger-scale science at national laboratories.”