Dark matter is a form of matter that we cannot see or detect directly with our usual instruments. Yet it appears to make up about 85% of the matter in the universe. Its existence was first proposed in the 1930s by Swiss astronomer Fritz Zwicky, who, observing clusters of galaxies, noticed that the visible matter was insufficient to explain their gravity: something was missing — a “missing mass.”

Since then, numerous observations, such as galaxy rotation curves and the large-scale structure of the universe, have confirmed that an unseen form of matter must exist to hold these cosmic systems together. We still do not know what it is made of: exotic particles, unknown massive particles, or other physical phenomena — dark matter remains a mystery.

Experiments around the world, underground and in space, are trying to detect it, measure its properties, and understand its role in the formation of the universe. Dark matter is invisible, but its influence shapes everything we see in the cosmos.

Gravitational lensing is a fascinating phenomenon predicted by Albert Einstein’s general relativity. According to this theory, the presence of mass warps the surrounding space-time. As a result, light emitted by distant galaxies can be bent when it passes near massive objects, such as galaxy clusters or black holes, forming luminous arcs, rings, or multiple images.

This bending of light acts as a true cosmic lens, allowing astronomers to observe extremely distant galaxies that would otherwise be invisible. Gravitational lenses are also a powerful tool for mapping dark matter: even though it is invisible, it bends light and reveals its presence.

Each gravitational lens tells a story about the universe: the path of light informs us about the mass, distribution, and structure of space-time. This phenomenon, invisible to the naked eye, thus becomes a way to “see” what cannot be observed directly.