What is dark matter?

Dark matter is a mysterious form of matter that does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects. It is thought to make up about 27% of the total mass and energy content of the universe, far outweighing the ordinary matter (like stars, planets, and gas) that we can see and study directly. Despite its invisibility, dark matter plays a crucial role in shaping the large-scale structure of the cosmos. Astronomers first inferred the existence of dark matter by observing the way galaxies and galaxy clusters move. For example, stars at the outer edges of galaxies orbit faster than expected based on the visible mass alone. This discrepancy suggests there is additional unseen mass providing the necessary gravitational pull. Dark matter acts as a kind of "cosmic scaffolding," influencing how galaxies form and cluster together over billions of years. Understanding dark matter is important because it helps explain many fundamental aspects of the universe’s evolution and structure. Without dark matter, current models of cosmology and galaxy formation would not match observations. Although scientists have not yet identified what dark matter is made of, ongoing experiments and observations aim to uncover its nature, which could revolutionize our understanding of physics and the universe.