Dark dwarfs, a theoretical subclass of brown dwarf stars believed to contain dark matter, may be the optimal objects in which to finally discover physical dark matter in the real world—potentially transforming it from a purely theoretical concept into observable reality, according to researchers from the United States and United Kingdom.
Dark matter is one of the most important unsolved mysteries in modern astrophysics. While scientists have not yet directly detected it, the vast majority accept its existence based on its observable gravitational effects. Still, researchers continue to debate what form dark matter may take, but only one candidate appears to be compatible with the formation of dark dwarfs.
Invisible Dark Matter
Most scientists agree that dark matter exists and can explain a range of astrophysical phenomena, including galaxy rotation curves, gravitational lensing, and the structure of the cosmic microwave background. However, its fundamental nature remains elusive. Because dark matter does not emit, absorb, or reflect light, it cannot be seen directly and is only detectable through its gravitational influence on visible matter.
“We think that 25% of the universe is composed of a type of matter that doesn’t emit light, making it invisible to our eyes and telescopes. We only detect it through its gravitational effects. That’s why we call it dark matter,” said co-author Jeremy Sakstein, Professor of Physics at the University of Hawai’i.
The international research team suggests beginning the search for dark matter in theoretical dark dwarfs, stars that would contain and be powered by dark matter. These would be small, low-mass stars, roughly 8% the mass of the Sun—too light to sustain hydrogen fusion, the process that powers ordinary stars. As a result, they would appear faint and difficult to detect.
WIMPs
“For dark dwarfs to exist, dark matter has to be made of WIMPs, or any heavy particle that interacts with itself so strongly to produce visible matter,” Sakstein says.
Weakly Interacting Massive Particles (WIMPs) are one of the leading candidates for dark matter. They are theorized to be massive particles that interact only via gravity and the weak nuclear force, making them extremely difficult to detect. Other candidates—such as fuzzy ultralight particles, axions, or sterile neutrinos—lack the properties needed to produce the kind of energy output expected in a dark dwarf. According to the team, only WIMPs or similarly massive particles could annihilate and release energy inside such stars.
“Dark matter interacts gravitationally, so it could be captured by stars and accumulate inside them. If that happens, it might also interact with itself and annihilate, releasing energy that heats the star,” Sakstein explains.
Theoretically, dark dwarfs may form when brown dwarfs reside in regions with high concentrations of dark matter, such as the center of the Milky Way galaxy. Over time, these stars could capture enough dark matter to produce detectable effects.
“These objects collect the dark matter that helps them become a dark dwarf. The more dark matter you have around, the more you can capture,” Sakstein explains. “And, the more dark matter ends up inside the star, the more energy will be produced through its annihilation.”
Observing the Dark Dwarfs
Although dark dwarfs remain hypothetical, the research team has proposed a method for identifying them. One key marker may be the presence of Lithium-7.
“There were a few markers, but we suggested the Lithium-7 because it would really be a unique effect,” Sakstein explains. “Lithium-7 burns very easily and is quickly consumed in ordinary stars. “So if you were able to find an object which looked like a dark dwarf, you could look for the presence of this lithium because it wouldn’t be there if it was a brown dwarf or a similar object.”
One of the most powerful tools currently exploring the universe beyond our solar system is the James Webb Space Telescope (JWST). Sakstein says that the advanced instruments aboard Webb may be capable of detecting a cool dark dwarf, but it’s not the only solution.
“The other thing you could do is to look at a whole population of objects and ask, in a statistical manner, if it is better described by having a sub-population of dark dwarfs or not,” Sakstein added.
The team says that eventually finding a dark dwarf will be a major step toward proving their WIMPs hypothesis.
“With light dark matter candidates, something like an axion, I don’t think you’d be able to get something like a dark dwarf. They don’t accumulate inside stars. If we manage to find a dark dwarf, it would provide compelling evidence that dark matter is heavy, interacts strongly with itself, but only weakly with the Standard Model.
“This includes classes of WIMPs,” Sakstein concludes, “but it would include some other more exotic models as well.”
The team’s recent paper, “Dark Dwarfs: Dark Matter-Powered Sub-Stellar Objects Awaiting Discovery at the Galactic Center,” appeared on July 7, 2025, in the Journal of Cosmology and Astroparticle Physics.
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.