What is the proposed type of matter that accounts for the missing mass in the Universe?

The proposed type of matter that accounts for the missing mass in the Universe is dark matter. This concept arose from observations that the gravitational effects of visible matter alone could not explain the movements and clustering of galaxies. Astronomers noted that galaxies rotate at such speeds that the visible mass, comprised of stars and gas, could not provide enough gravitational pull to hold them together.

Dark matter is theorized to make up a significant portion of the total mass in the universe, helping to create the gravitational scaffolding that influences the motion of galaxies and galaxy clusters. Unlike normal matter, which emits light and can be observed directly, dark matter does not interact with electromagnetic forces, making it invisible and detectable only through its gravitational effects.

In contrast, normal matter and visible matter refer to the ordinary matter that we can see and measure—things like stars, planets, and galaxies—while "black matter" is not an established scientific term. Thus, dark matter is essential for understanding the structure and formation of the universe, as well as the distribution of galaxies.