Astronomers now propose that “failed stars” known as brown dwarfs could be powered by dark matter. Dark matter makes up about 85 percent of the universe’s matter but does not shine; it interacts only via gravity. Brown dwarfs form like stars but lack enough mass to ignite fusion. The theory suggests brown dwarfs in galaxy centers might trap dark matter in their interiors. When that dark matter annihilates, it releases energy that heats the star, turning the dwarf into a brighter “dark dwarf.” If such objects exist, finding them would give scientists a new clue to the nature of dark matter.

Dark Matter in Failed Stars

According to the new model, dense brown dwarfs at the centers of galaxies act like gravity wells that accumulate dark matter. Because dark matter interacts only via gravity, it naturally drifts to galactic cores, where it can be captured by star. As University of Hawai‘i physicist Jeremy Sakstein explains, once inside a star dark matter can annihilate with itself, releasing energy that heats the dwarf. The more dark matter a brown dwarf collects, the more energy it outputs. Crucially, this effect only works if dark matter particles self-annihilate (as with heavy WIMPs); lighter or non-interacting candidates like axions would not create dark dwarfs.

They propose using a chemical signature: a dark dwarf should hold on to lithium-7 that normal brown dwarfs burn away. The researchers say powerful telescopes like NASA’s James Webb Space Telescope might already be sensitive enough to spot cool, dim dark dwarfs near the Milky Way’s center. Detecting even one would strongly suggest that dark matter is made of heavy, self-interacting particles (like WIMPs).

In related work, Colgate astrophysicist Jillian Paulin coauthored studies of ancient “dark stars” fueled by dark matter, while SLAC physicist Rebecca Leane and collaborators have shown that dark matter capture could heat brown dwarfs and exoplanets – a process called “dark kinetic heating”. Together, these ideas highlight how even dim, unusual stars could illuminate the nature of dark matter.