For nearly a century, scientists have puzzled over the invisible substance believed to make up the majority of our universe: dark matter. Despite being first described back in the 1930s, dark matter remains one of the most mysterious components of the cosmos. It neither reflects nor absorbs light, and it interacts with normal matter only through gravity, making it notoriously difficult to detect. As of August 19, 2025, most experts agree that dark matter is real, though a handful of scientists still question its existence, and our understanding of it is far from complete, according to Discover Magazine.
"Dark matter is basically an invisible component of matter," explained Shyam Balaji, a Postdoctoral Research Fellow in the Department of Physics at King's College London, in an interview with Discover Magazine. "All the stuff that we are made of — all the baryonic matter as we call it — the stars, planets, people, all the chemical elements that you see in the universe; all of that stuff is only a very small component of the actual matter." In fact, normal, or baryonic, matter makes up only about 5 percent of the universe. In contrast, dark matter is thought to account for as much as 27 percent, with the remaining 68 percent comprising dark energy.
Yet, despite its enormous role in the cosmos, no scientist or astronomical agency has ever directly observed dark matter. Its existence is inferred from its gravitational effects on visible matter. One of the most compelling pieces of evidence comes from gravitational lensing, a phenomenon where massive objects like galaxy clusters bend light from objects behind them. "It basically acts just like a lens," Balaji said. This effect suggests there is more mass present than what can be seen, leading astronomers to conclude that dark matter must be at work.
To get closer to the truth, researchers have built highly sensitive sensors deep underground, such as the detector located 4,850 feet beneath the Sanford Underground Research Facility in South Dakota. These instruments are designed to pick up the faint interactions between dark matter and normal matter, often using substances like liquid xenon or argon. The hope is that, shielded from cosmic radiation and other interference, these detectors might one day register a dark matter particle in action. The search is ongoing, with more advanced sensors in development, according to Discover Magazine.
Much of the speculation about dark matter's composition centers on the idea of weakly interacting massive particles, or WIMPS. These hypothetical particles would interact with normal matter only via gravity and possibly the weak nuclear force. However, as Balaji pointed out, "At this point, we don't know exactly what dark matter is made of, or what its properties are, or how strongly it interacts with normal matter." The mystery deepens when considering that, if dark matter interacted more strongly, it would simply be another form of ordinary matter.
But what would happen if a human came into contact with dark matter? According to Discover Magazine, the odds are vanishingly small. Dark matter's weak interactions mean it passes through normal matter almost entirely unimpeded. "If it was strongly interacting, dark matter would just be a normal form of matter," Balaji noted. Some researchers have even explored the possibility that if dark matter existed in large, macro-sized clumps, it might occasionally collide with humans, leaving unexplained bullet-sized wounds. But no such injuries have ever been documented, suggesting that dark matter, at least in that form, does not exist.
Another theory proposes that dark matter could consist of primordial black holes—tiny black holes with the mass of an asteroid, formed shortly after the Big Bang. A collision with such an object would be catastrophic, but the probability of this happening is, as Balaji put it, "astronomically tiny." He added, "You'd have to be extremely, extremely unlucky, like extremely unlucky to the power of a huge number for it to happen." So, while the prospect is chilling, it's not something anyone should lose sleep over.
Yet, the story of dark matter took an intriguing turn this month with the publication of new research in the Astrophysical Journal Letters on August 7, 2025. According to Space.com, astronomers have been studying Ursa Major III (UMa3/U1), the faintest known satellite of the Milky Way. Located more than 30,000 light-years from Earth, this compact stellar system contains only 60 visible stars. For years, it was thought to be a dark matter-dominated dwarf galaxy, due to its unusually high mass-to-light ratio. That is, there seemed to be much more mass present than could be accounted for by its visible stars—classic evidence for dark matter.
However, a team led by researchers at the University of Bonn in Germany has now upended this assumption. Using computer simulations and precise measurements of Ursa Major III's orbital motion and chemical composition, they reconstructed the object's history. Their findings suggest that, over billions of years, gravitational interactions with the Milky Way stripped away the cluster's outer stars, leaving only a dense, invisible core. This core, the team argues, is not made of dark matter, but rather a concentration of black holes and neutron stars—the remnants of massive stars that once populated the cluster.
"Dark star clusters form when gravitational interactions with the Milky Way over billions of years remove the outer stars from a star cluster," explained Hosein Haghi, co-author of the study, in a statement released by the University of Bonn and reported by Space.com. After repeated encounters, only the dense, dark core remains. Since this core emits no light, it was initially mistaken for being made of dark matter.
The simulations demonstrated that the gravity of this compact core could hold the remaining stars together, without invoking dark matter. "Our work shows for the first time that these objects are most likely normal star clusters," said Pavel Kroupa, another co-author. "These results solve a major mystery in astrophysics." The discovery suggests that at least some objects previously thought to be dominated by dark matter may, in fact, owe their stability to concentrations of black holes and neutron stars.
This finding doesn't disprove the existence of dark matter, but it does remind scientists to keep an open mind. The universe, as always, is full of surprises. As astronomers continue to probe the cosmos with ever more sophisticated tools, they may yet uncover the true nature of dark matter—or perhaps find that the answer is even stranger than anyone imagined.
For now, the search goes on, deep underground and far out in space, as researchers strive to illuminate one of the universe's darkest secrets.
