Size comparison of universe and galaxy
Pro Research Analysisby 
Searched over 200M research papers
Universe Size vs. Galaxy Size: Key Scale Differences
The universe is vastly larger than any single galaxy. While galaxies are massive collections of stars, gas, and dark matter, the universe contains billions of galaxies spread across immense distances. The mass of the universe is many orders of magnitude greater than the mass of any individual galaxy, and the spatial scale of the universe dwarfs that of even the largest galaxies .
Typical Galaxy Sizes and Masses
Spiral and Other Galaxies
Spiral galaxies, such as the Milky Way, have masses on the order of 10 billion solar masses and their mass increases almost linearly with radius up to nearly 1 megaparsec (Mpc) from the center . The physical size of galaxies varies widely, but typical half-light radii (the radius within which half the galaxy's light is emitted) for large galaxies like the Milky Way are around 5–6 kiloparsecs (kpc) . For context, 1 kpc is about 3,260 light-years.
Variation Across Galaxy Types and Ages
Galaxy sizes depend on their type and evolutionary stage. For example, early-type (bulge-dominated) galaxies and quiescent (non-star-forming) galaxies are generally more compact than star-forming galaxies of similar mass 4679. At high redshifts (when the universe was younger), galaxies were typically smaller and more concentrated, with some faint galaxies as small as 10–30 parsecs (pc), similar in size to large star clusters . Over time, galaxies grow in size due to processes like star formation, mergers, and the outward migration of stars 56910.
The Milky Way as a Reference
Recent measurements show the Milky Way has a half-light radius of about 5.75 kpc, which is larger than previously thought and consistent with other local disk galaxies of similar mass . This size reflects a more complex structure than the simple exponential disk model used in the past.
The Universe: Immense Scale and Mass
The observable universe spans about 93 billion light-years in diameter, containing an estimated two trillion galaxies. The total mass of the universe is not precisely known but is vastly greater than the combined mass of all galaxies within it . The mean cosmological mass density is uncertain but is at least a factor of three higher than local measurements, highlighting the universe's immense scale compared to individual galaxies .
Conclusion
In summary, a single galaxy like the Milky Way is enormous on a human scale, spanning tens of thousands of light-years and containing billions of stars. However, compared to the universe, even the largest galaxies are minuscule. The universe is billions of times larger and more massive, containing countless galaxies separated by vast distances. This immense difference in scale is a fundamental aspect of cosmology and our understanding of the universe's structure 110.
Sources and full results
Most relevant research papers on this topic