Final answer:
The largest known structures in the universe are superclusters, which are vast assemblies of galaxy clusters bound together by gravity, stretching over hundreds of millions of light-years and comprising less than 10% of the total volume of space.
Step-by-step explanation:
The largest known scale of structures in the universe, consisting of groups of galaxy clusters gravitationally bound to one another, are called superclusters. These enormous structures can stretch over several hundred million light-years and are composed of many galaxy clusters interconnected by filaments, creating a vast cosmic network.
Galaxy clusters are themselves groups of galaxies, with some well-known examples being the Local Group, Virgo, and Coma clusters. Our own galaxy, the Milky Way, is part of the Local Group, which comprises over 50 member galaxies. These clusters of galaxies, grouped further into superclusters, create a filamentary layout that represents a substantial fraction of the observable universe, though still occupying less than 10% of the total volume of space. The superclusters and the vast voids between them form a sponge-like structure enveloping the cosmos.
Astronomers have been able to map these structures three-dimensionally, taking into account the position and distance of galaxies. The distribution and formation of these colossal structures, as well as the role of dark matter and dark energy in shaping them, are fundamental components in our understanding of the cosmos. Current models suggest that a mixture of 5% normal matter, 27% cold dark matter, and 68% dark energy best describes the composition necessary for the development of such structures.