Dark matter refers to the invisible mass in the universe which seems to account for ~27% of the mass of our entire universe. Just for context, the mass we can actually see with our eyes—ordinary matter—accounts for only ~5%. The rest is "dark energy."

Dark matter is responsible for the rotation of galaxies and clusters of galaxies in our universe. When we measure the rotational motion of these bodies, the rotational speed is found to be too fast to be explained by ordinary matter alone. There seems to be some lurking matter which has no interaction with traditional electromagnetism. Measurements of the radiation from the early universe also seem to support the presence of dark matter.

There are two ways to rationalise the concept of dark matter. One is that our current best model of gravity—general relativity—is perhaps not as accurate as we thought. The other is that dark matter is a new kind of particle to be added to the existing standard model of particle physics. Numerous particle physics experiments have attempted to search for different dark matter candidates. If a dark matter particle interacts with and/or produces a standard model particle, we may be able to infer the presence of dark matter.

In 2023, Janish & Pinetti published a paper using astrophysical data—measurements of infrared photons from the background of the sky—to hunt for dark matter. They used portions of data containing blank sky to analyse the background of measurements from other objects. It is said that every galaxy sits in a dark matter halo. If we look out into the blank sky, we also can't avoid staring into such a halo, and thus into some invisible volume filled with dark matter particles. In some theories, a dark matter particle may decay into two photons or a photon and some other particle. In this case, the wavelength of the produced photon can also tell us about the mass of the dark matter candidate. By looking at infrared photons in the blank sky, if an excess number of photons is seen, this could point to a potential presence of dark matter.

As a first test, the authors compare various models of flux spectra, each with different rates of photon emission, to the total flux of infrared photons from JWST data for a specific dark matter mass. The authors then complete a second kind of test. In this case, a model is used for the entire flux spectrum that is then compared to the data at individual wavelengths. This approach allows them to look for an emission line that could belong to a dark matter candidate. They found three models for emission lines that are significant, but not strong enough to be dark matter candidates.

This study represents a significant step forward int he search for dark matter. While no strong evidence of dark matter was found, their analysis placed new constraints on the possible decay rates of dark matter candidates, particularly for axion-like particles. With more JWST data, detections of infrared background photons will increase over time. As shown in the figure above, this will lead to stronger constraints in the coming years as the data quality improves. A major advantage to this test is that it doesn't require dedicated telescope time—it can use background signals from other images.

published: 16/02/25 by kaan evcimen