Researchers propose that dark matter could be composed of macroscopic, star-sized objects such as boson stars or Q-balls. These Exotic Astrophysical Dark Objects (EADOs) would be dark but detectable via brief, distinctive gravitational microlensing shifts of background stars. The Gaia space telescope, with its long-term, high-precision astrometry, is well suited to find such events. A dedicated Gaia search could uncover up to thousands of EADOs or place strong constraints on their contribution to dark matter.
Could Dark Matter Be Star-Sized? Astronomers Propose Using Gaia to Find Exotic Objects
There are many particle candidates for what makes up dark matter. . | Credit: Naeblys/Getty Images
Exotic, nonluminous objects roughly the size of stars could make up some or all of the Universe's dark matter — and astronomers say the Gaia space telescope may already have the data needed to find them.
What Are These Exotic Objects?
Researchers exploring alternatives to particle dark matter have focused on two classes of macroscopic candidates, both of which fall under the umbrella of Exotic Astrophysical Dark Objects (EADOs).
Boson Stars
In this scenario, dark matter is composed of an ultralight boson — potentially millions of times lighter than neutrinos. Because of their extreme lightness, these particles behave more like coherent waves on galactic scales than like individual particles. Under gravity, those waves can self-gravitate and form extended, stable configurations known as boson stars.
Q-Balls
Q-balls arise from a different mechanism: a pervasive quantum field occasionally concentrates into giant, long-lived, ball-like lumps. Far from elementary particles, these localized field configurations can behave as macroscopic, stable objects drifting through space.
How Would We Detect Them?
Both boson stars and Q-balls are roughly star-sized yet emit no light, so they are effectively invisible to conventional telescopes. However, their gravity can reveal their presence through gravitational microlensing. If an EADO passes between Earth and a background star, its gravity can temporarily shift the apparent position of the star, producing a brief, characteristic positional jump as seen from our vantage point.
Why Gaia Is Ideal
The European Space Agency's Gaia mission repeatedly measures the positions of over a billion stars with unprecedented precision. That long-term, high-accuracy monitoring makes Gaia uniquely suited to search for the transient positional signatures expected from EADOs.
The Proposed Search and Outcomes
The study, posted to the open-access server arXiv in November 2025, outlines a targeted campaign to comb Gaia data for the rapid, distinctive microlensing signatures of Q-balls and boson stars. Depending on their abundance in the Milky Way, Gaia could already contain signals from up to thousands of EADOs. Conversely, a null result would translate into stringent new limits on how much these objects can contribute to the dark matter budget.
Bottom line: A dedicated Gaia search could either reveal a new, macroscopic form of dark matter or rule out a large portion of the parameter space for these exotic candidates — either outcome would be a major advance in understanding dark matter.
