Size comparison universe vs galaxy

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Universe vs Galaxy Size: Scale and Comparison

Universe Size and Mass: Cosmological Scale Keywords

The universe is vastly larger than any single galaxy. While the exact size of the universe is not definitively known, it is understood to be at least tens of billions of light-years across, possibly infinite. In contrast, the mass of the universe is many orders of magnitude greater than the mass of any individual galaxy, with the local mean cosmological mass density being much higher than the mass contained in a single galaxy. For example, a giant spiral galaxy typically has a total mass of about 10 billion solar masses and a size extending up to nearly 1 megaparsec (Mpc), or about 3.26 million light-years, but this is minuscule compared to the universe as a whole .

Galaxy Size: Range and Variation Keywords

Galaxies themselves vary greatly in size. Typical spiral galaxies can have radii up to about 1 Mpc, but most are much smaller. Observations and simulations show that galaxy sizes increase with stellar mass, but even the largest galaxies are tiny compared to the universe. For example, faint galaxies in the early universe can be as small as 10–500 parsecs (pc), with some star-forming regions as compact as 10–30 pc . More massive galaxies at different epochs can have half-light radii of a few kiloparsecs (kpc), and the largest galaxies in clusters can reach sizes of several tens of kpc 345678.

Size Evolution: Galaxies Over Cosmic Time Keywords

Galaxy sizes have evolved over cosmic time. In the early universe, galaxies were generally smaller and more compact, with sizes growing as galaxies merged and accumulated more mass. Simulations and observations show that galaxy sizes increase with time, but even the largest galaxies remain extremely small compared to the universe itself 45678. The size of a typical galaxy is measured in kiloparsecs, while the observable universe is measured in gigaparsecs (billions of parsecs).

Direct Size Comparison: Universe vs Galaxy Keywords

To put the scale in perspective:

A typical large galaxy, such as the Milky Way, is about 30 kpc (about 100,000 light-years) in diameter.
The observable universe is at least 28,000,000,000 parsecs (about 93 billion light-years) in diameter.

This means the universe is about a million times larger in diameter than a typical galaxy, and the difference in volume is even more extreme 17.

Conclusion

In summary, galaxies are incredibly small compared to the universe. While galaxies can be massive and span tens to hundreds of thousands of light-years, the universe itself is billions of light-years across. The size and mass of a single galaxy are negligible when compared to the entire universe, highlighting the vastness of cosmic scales 12345678.

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Most relevant research papers on this topic

The size and mass of galaxies, and the mass of the universe

The mass of spiral galaxies increases linearly with radius to nearly 1 Mpc, with a local mean cosmological mass density of about 10 billion solar masses.

Highly Cited

1974·

303citations

·J. Ostriker et al.

Low-luminosity Galaxies in the Early Universe Have Observed Sizes Similar to Star Cluster Complexes

Low-luminosity galaxies in the early universe have sizes similar to star cluster complexes, suggesting we may be close to discovering a population of forming globular clusters at high redshift.

2021·

12citations

·R. Bouwens et al.

Environmental dependence of bulge-dominated galaxy sizes in hierarchical models of galaxy formation. Comparison with the local Universe

The data shows no significant environmental dependence of early-type galaxies, contradicting hierarchical models of galaxy formation, and suggests discrepancies in disc instabilities and short quenching time-scales.

2014·

58citations

·F. Shankar et al.

Rest-frame Near-infrared Sizes of Galaxies at Cosmic Noon: Objects in JWST's Mirror Are Smaller than They Appeared

Galaxy sizes are 9% smaller at 4.4 m than 1.5 m, with stronger effects at higher stellar masses and redder rest-frame colors.

2022·

45citations

·K. Suess et al.

Size evolution of star-forming galaxies with 2

Star-forming galaxies with a median size of 2 : 2 kpc have a relatively constant size, with the largest at any redshift being more massive and forming more stars, while their light profiles become more concentrated with increasing redshift.

2016·

43citations

·B. Ribeiro et al.

Size evolution of normal and compact galaxies in the EAGLE simulation

The EAGLE simulation shows that galaxy sizes increase with stellar mass, but the relation weakens with increasing redshift, and passive galaxies are typically smaller than active galaxies at a fixed stellar mass.

Highly Cited

2015·

147citations

·M. Furlong et al.

Galaxy size trends as a consequence of cosmology

Galaxy size trends can be understood as an emergent consequence of cosmic expansion, with the observed minimum radius for galaxies, the evolving trend in size as a function of mass for intermediate systems, and the increase in massive galaxies.

2013·

17citations

·M. Stringer et al.

The thesan project: galaxy sizes during the epoch of reionization

Galaxy sizes at redshift z 6 show a hump feature and a lack of compact galaxies, suggesting the potential for galaxy morphology to constrain galaxy formation at high redshifts.

2024·

4citations

·Xuejian Shen et al.

Galaxy sizes and the galaxy–halo connection – I. The remarkable tightness of the size distributions

The data require extremely tight relations between galaxy size and host dark matter halo virial radius, challenging models based solely on angular momentum conservation.

2019·

20citations

·L. Zanisi et al.

The Size–Mass Relation of Post-starburst Galaxies in the Local Universe

Post-starburst galaxies in the local universe have smaller galaxy sizes than quiescent galaxies, with fast quenching of star formation following a short-lived starburst event being the dominant evolutionary pathway.

2022·

3citations

·Xinkai Chen et al.

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