What is dark matter?

Dark matter is a form of matter that does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects on visible matter, such as stars and galaxies. In the study of galactic dynamics, scientists have observed that galaxies rotate at speeds that cannot be explained solely by the visible matter they contain. If only the mass from stars, gas, and dust were considered, the outer regions of galaxies would rotate much more slowly than observed. The unexpected gravitational pulling indicates there must be additional unseen mass—this is what we refer to as dark matter.

Thus, the concept of dark matter is fundamentally grounded in these gravitational effects, which allow astronomers to infer its presence even though it cannot be directly observed or measured in traditional ways. The understanding of dark matter plays a crucial role in cosmology, influencing the behavior of galaxies and the structure of the universe itself.