The search for dark matter may be far more complex than scientists assume, as new research suggests that contradictory clues may point to two distinct forms of the theoretical substance.
Published in the Journal of Cosmology and Astroparticle Physics, a new study says that astrophysicists don’t need to look for the same indications in every instance as they search for hidden dark matter, a substance thought to account for more than half of the universe’s total matter.
The American team behind the new work, including researchers from Fermi National Accelerator Laboratory (Fermilab), says the search for dark matter may be even more complex than previously estimated, since differing ratios of dark matter types could potentially produce distinctive signatures. Such a determination, if proven, could help to account for why this mysterious non-luminous substance remains so elusive.
Debating the Nature of Dark Matter
The team examined potentially conflicting information, which has sparked debate over the best way to search for dark matter. For example, while a signal from the center of the Milky Way may represent gamma radiation from the annihilation of dark matter particles, that signal may not be detectable from certain other galaxies.
This raises questions about whether this signal is related to dark matter, since it should be abundant everywhere. But not so fast, according to the team behind this latest research, which suggests that dark matter may be more than a single particle, meaning that its behavior varies throughout the universe.
“If certain theories of dark matter are true, we should see it in every galaxy, for example, in every dwarf galaxy,” said Gordan Krnjaic, a theoretical physicist at Fermilab.
While astrophysicists believe that dark matter exists and is abundant in the universe, because it has never been directly observed, they cannot be certain of its nature. While gravitational effects on matter have led researchers to infer the presence of dark matter, no concrete confirmation has yet been obtained.
Modeling Dark Matter
Dark matter is often modeled as particles that annihilate when they come into contact, producing high-energy gamma rays. Two scenarios for dark matter particle annihilation have been proposed: one in which the likelihood is constant, and the other in which the probability of annihilation is determined by the speed of the particles.
The steady signals from our galaxy best align with the steady probability prediction. In the speed-determined model, it’s expected that annihilations would be rare, leaving almost no signal for astrophysicists to detect, aligning with the silence of dwarf galaxies.
“Right now there seems to be an excess of photons coming from an approximately spherical region surrounding the disk of the Milky Way,” Krnjaic said.
In Fermi Gamma-ray Telescope observations, researchers have detected the large number of gamma-ray photons expected from such annihilations. Still, there are other explanations, such as a large population of pulsars, that could also produce them.
With fewer objects to create noise, dwarf galaxies are an ideal place to observe dark matter, something they are expected to be rich in. Yet when scientists look for these signals in these regions of the cosmos, they find nothing.
A More Complex Dark Matter Scenario
Instead of viewing the silence of dwarf galaxies as proof that the Milky Way’s gamma radiation is unrelated to dark matter, the researchers suggest there may be two distinct types of dark matter particles, and that they may behave differently.
“What we’re trying to point out in this paper is that you could have a different kind of environmental dependence, even if the annihilation probability is constant in the center of the galaxy,” explained Krnjaic. “Dark matter could straightforwardly be two different particles, and the two different particles need to find each other in order to annihilate.”
The researchers further suggest that the ratio of one particle type to another in a given locality will determine how much dark matter is annihilating there. Their explanation for dwarf galaxies is that they must be heavily biased toward speed-dependent annihilations.
“In this way, you get very different predictions for the emission,” added Krnjaic.
The team says that data on dwarf galaxies are currently limited, and that further observations by the Fermi Gamma-Ray Telescope will provide a clearer picture of whether these galaxies are producing gamma radiation.
The paper, “dSph-obic Dark Matter,” appeared in Journal of Cosmology and Astroparticle Physics on April 9, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.