Unlocking the Universe’s Greatest Secret
“We don’t know what dark matter is, and there is no theory that explains it.” The bluntness with which astrophysicist Jorge Sánchez refers to this informational black hole is significant. Comprising nearly 85% of the cosmos, this mysterious substance remains one of the universe’s best-kept secrets. The answer to the puzzle, however, might lie in the smallest galaxies. Indeed, a group of researchers from the islands has used one of these dwarf galaxies to propose a new theory on how dark matter is distributed in space—a fresh explanation that aligns with observations and, according to Sánchez, could help reveal what exactly is hiding in the darkness.
Challenging the Standard Model
The premise of this research group—which has published its results in the journal Astronomy and Astrophysics—is that the only way to detect dark matter is through its interactions with the rest of the medium. “Until now, the standard model—the most widely accepted one—states that the only interaction between galaxies and dark matter is gravity, and that it is this interaction which distributes the dark matter,” explains Sánchez. Consequently, this explanation concludes that “the particles that make up dark matter do not talk to each other.” In other words, dark matter exists in isolation from itself but is distributed depending on the stars that surround it.
The Problem with Tiny Galaxies
This theory has helped unravel many circumstances related to dark matter but has fallen short when confronted with reality. “This theory predicts that processes in the centres of galaxies—supernova explosions, gas movements, and other types of cosmic phenomena—are energetic enough to, through gravity, redistribute dark matter,” he reveals. However, this theory—which Sánchez notes is only an approximation—cannot explain what happens in very small galaxies. “There are so few stars and ordinary matter in their centre that it is impossible for them to have any effect on the dark matter.”
These galaxies, which contain barely a few thousand stars, are dominated by dark matter and have had very simple evolutionary histories, making them ideal cosmic laboratories for testing theories on dark matter physics. “There had to be another interaction beyond gravity, even if it was very weak,” explains Sánchez.
A Rare Interaction Holds the Key
The newly published study demonstrates that extremely infrequent interactions between dark matter particles can naturally generate the central structures—or “cores”—that are observed, formations that traditional collisionless dark matter models struggle to reproduce easily. “All particles, including dark matter particles, must eventually interact via forces that go beyond gravity. Our study shows that even extremely rare interactions can leave observable footprints in the smallest galaxies,” he adds.
Their explanation assumes that a single collision between dark matter particles every 10 billion years—approximately the age of the Universe—is enough to explain the dark matter cores observed in these diminutive systems.
A First Step Towards the Truth
Despite these deviations from theoretical dark matter models relative to the standard model, this contribution is significant not for its potential to change the standard model, “but because it could allow us to find observables that tell us something about the nature of dark matter.” In essence, the contribution of these Canary Islands researchers is the first step towards finally unravelling one of the cosmos’s best-kept mysteries.
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