The Universe, as we see it, is only the tip of the iceberg. In 1933, astrophysicist Fritz Zwicky made a groundbreaking discovery while studying the Coma Cluster—a massive collection of galaxies. By comparing the cluster’s total mass (as estimated from its brightness) with the mass inferred from the movement of its galaxies, he found a massive discrepancy. The galaxies were moving so fast that, based on visible matter alone, they should have flown apart. Yet, they didn’t. Something unseen was holding them together, something that didn’t emit or interact with light. Zwicky called this invisible mass Dunkle Materie—dark matter.
Dark Matter
Only 5% of the Universe's composition falls within our current knowledge. About 26% consists of an unknown, massive substance called dark matter, while the majority—around 69%—is dark energy, an even greater mystery than dark matter.
For decades, the search for dark matter has been more active than ever, with numerous candidate theories and experiments pushing the boundaries of our understanding.
Evidence
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Beyond individual galaxies, compelling evidence for dark matter (DM) emerges on even larger cosmic scales—particularly in galaxy clusters. One of the most striking examples comes from the Bullet Cluster, where a dramatic cosmic collision provided a rare glimpse into the unseen.
When two galaxy clusters collided, astronomers observed something fascinating. Using weak gravitational lensing—a phenomenon where massive objects bend light from distant sources—they mapped the distribution of mass. The result? A clear separation between ordinary matter and something else.
Candidates
- Because of its unknown nature, dark matter has a diverse range of possible candidates spanning many orders of magnitude in mass. From ultra-light axions in the microelectronvolt (µeV) range, heavy WIMPs reaching the TeV scale, to primodial black holes, various theories predict different particles as the key to solving this cosmic puzzle.
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- This graph illustrates the vast landscape of proposed dark matter candidates, through the mass ranges. While past research has focused primarily on GeV-TeV scale WIMPs, the field is now shifting towards lighter candidates below the MeV scale. Detecting such particles presents new challenges, requiring ultra-sensitive detectors capable of resolving tiny energy deposits. The QROCODILE experiment is at the forefront of this search. By utilizing cryogenic superconducting sensors, it explores the low-energy frontier, probing dark matter interactions down to 30 keV.