Final answer:
The composition of a galaxy is typically observed through the distribution of stars, gas, and dark matter, with galaxies containing significant amounts of low-mass stars contributing to a high mass-to-light ratio. The universe, on the other hand, is largely composed of regular matter, dark matter, and dark energy, with dark components forming 95% of its makeup and influencing the large-scale structure. Cosmologically, the universe is homogeneous and isotropic, though galaxies group into complex structures like clusters and superclusters.
Step-by-step explanation:
The composition of a galaxy compared to the composition of the universe is a fascinating aspect of cosmology, which is the study of the character and evolution of the universe. Within the universe, matter is distributed across approximately 10ยนยน galaxies, which form together in structures such as clusters and superclusters. The Milky Way Galaxy, as a part of the Local Group, is one of these galaxies, containing more stars and being slightly larger than the average galaxy.
While we see significant clouds of gas, stars, and a mysterious component known as dark matter in galaxies, the universe's largest composition includes regular matter, dark matter, and dark energy. Regular matter, which is familiar to us on Earth, only comprises around 5% of the universe, with most of it consisting of hydrogen and helium. Dark matter and dark energy make up the remaining 95%, and they have an immense impact on the universe's structure, but remain undetectable in Earth-bound laboratories.
Galaxies, as enormous collections of stars, gas, and other materials, have a mass-to-light ratio generally greater than 1, indicative of more mass being present than the light we can see. This is primarily due to the preponderance of low-mass stars in galaxies which contribute significantly to the overall mass without adding much light. In contrast, the Universe's composition is largely uniform and isotropic following the cosmological principle, differing primarily in its large-scale structure shaped by the distribution of dark matter and energy.