Yes, it is true that the existence of dark matter is inferred primarily from its gravitational effects on visible matter and structures in the universe. Dark matter does not emit, absorb, or reflect electromagnetic radiation, making it invisible and difficult to directly detect.
The evidence for dark matter comes from various observations at different scales, including the rotation curves of galaxies, the motions of galaxies within galaxy clusters, the gravitational lensing of light, and the large-scale structure of the universe.
For example, observations of the rotational velocities of stars and gas in galaxies indicate that there is more mass present than can be accounted for by visible matter alone. The visible matter in galaxies is not sufficient to explain the observed gravitational forces that hold galaxies together, suggesting the presence of additional invisible matter, which we call dark matter.
Similarly, the motions of galaxies within clusters suggest the presence of a significant amount of unseen matter that provides the gravitational glue holding the clusters together.
Gravitational lensing, the bending of light by gravity, also provides evidence for the existence of dark matter. The distribution of dark matter can cause the bending of light from distant galaxies, creating gravitational lensing effects that can be observed and analyzed.
Moreover, the large-scale structure of the universe, as revealed by cosmic microwave background radiation and galaxy surveys, indicates that the distribution of matter is not uniform but shows clumps and filaments. Dark matter is thought to be responsible for the gravitational pull that shapes and influences the formation of these structures.
While the gravitational evidence for dark matter is compelling, the exact nature of dark matter particles remains unknown. Numerous experiments are underway to directly detect and study dark matter particles, but so far, no direct detection has been confirmed. The search for dark matter is an active area of research in astrophysics and particle physics.