11-05-2025
Dark matter may escape, but dark photons can't. Here's how MADMAX could catch them
Everything we visualize about space, including stars, planets, gases, and even galaxies, make up just a small fraction of the universe's total mass. The rest is invisible, silent, and frustratingly elusive, famously known as dark matter.
Scientists have tried numerous ways to catch this mysterious form of matter, but it has managed to allude researchers almost every time. However, the latest results from MADMAX (MAgnetized Disc and Mirror Axion eXperiment) suggest we're closer than ever to detecting dark matter.
MADMAX is a special setup that focuses on detecting axions and dark photons, two supposed particles that are believed to form the dark matter.
"These two hypothetical particles are popular candidates for what dark matter might consist of. In our recent paper, we describe the results of a search for dark photons using a small-scale prototype," Jacob Mathias Egge, first author of the study, and a PhD candidate at the University of Hamburg, said.
The challenge of detecting dark matter is not just that it is invisible—rather that it interacts so weakly with normal matter that we might never notice it unless we build incredibly sensitive instruments.
Traditional detectors have mostly come up empty-handed, especially when looking for heavier, slow-moving dark matter particles. That's why scientists have been turning their attention to lighter, more ghost-like particles like axions and dark photons.
MADMAX tackles this challenge with a clever setup. The main highlight of its design is a dielectric haloscope, a kind of detector that uses special materials and mirrors to amplify the tiny signals that dark matter particles might produce.
The MADMAX prototype uses three round discs made of sapphire, a pure and insulating material known for its excellent properties at high frequencies. These discs are spaced carefully in front of a mirror.
If dark photons exist, they might occasionally transform into ordinary photons (particles of light) when passing through materials with the right properties. The layered discs and the mirror are arranged so that this transformation is amplified at specific frequencies, similar to how tuning a radio to the right station turns a faint signal into a clear one.
Any resulting microwave photons from this process are then directed into a horn antenna, where an ultra-sensitive receiver tries to detect them. 'In our case, we tried to detect these excess photons with a frequency around 20 GHz," Egge said.
Although the researchers did not find a signal, they were able to rule out the presence of dark photons in this mass range at an unprecedented level of sensitivity, many many times better than previous efforts at similar frequencies.
"This is the first physics result from a MADMAX prototype and exceeds previous constraints on χ in this mass range by up to almost three orders of magnitude," the study authors note.
What makes this result especially exciting is that the MADMAX team has now proven that their approach works. This is the first time a prototype like this has been successfully used to probe dark photons, and it delivered impressive results.
"Since the core detector concept has now been proven to work, we can now easily expand our reach in the next upgraded iterations, increasing our chances of a detection," Egge added.
The biggest upgrade that is underway is to cool the entire detector down to just 4 Kelvin (-269°C). At such extremely low temperatures, thermal noise drops significantly, making the detector even more sensitive to tiny traces of dark matter.
Moreover, the current experiment only focuses on dark photons, but in future experiments, scientists will operate MADMAX under strong magnetic fields so that it could also detect axions at the same time.
The study has been published in the journal Physical Review Letters.
