Number of galaxies in visible universe

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Number of Galaxies in the Visible Universe

Estimating Galaxy Numbers: Challenges and Methods

Estimating the number of galaxies in the visible universe is a complex task due to biases and incompleteness in astronomical surveys. These surveys often miss faint and distant galaxies, making it difficult to get an accurate count . However, advancements in observational techniques and deep field surveys have provided more reliable estimates.

Current Estimates: Hundreds of Billions to Trillions

Recent studies suggest that there are about 100 billion galaxies in the observable universe . This estimate is based on current observational evidence and the average number of stars per galaxy. However, more detailed studies indicate that the actual number could be significantly higher. For instance, using galaxy stellar mass functions up to a redshift of z ≈ 8, researchers have estimated that the total number of galaxies could be around 2 trillion, which is almost ten times higher than what would be observed in an all-sky survey at Hubble Ultra-Deep Field depth .

Evolution of Galaxy Number Density

The number density of galaxies has evolved over time. Studies show that the total number density of galaxies more massive than M* = 10^6 M☉ decreases as the universe ages, following a trend of φT ∼ t^−1, where t is the age of the universe. However, this trend reverses for galaxies with higher mass limits (M* > 10^7 M☉), indicating an increase in number density over time .

Implications for Galaxy Evolution and Cosmology

These findings have significant implications for our understanding of galaxy evolution and cosmology. The higher number of galaxies suggests that many faint galaxies contribute to the cosmic background light in the optical and near-infrared spectra. This also helps address Olbers' paradox, which questions why the night sky is dark despite the vast number of stars .

Conclusion

In summary, while traditional estimates put the number of galaxies in the observable universe at around 100 billion, more recent and detailed studies suggest that the actual number could be as high as 2 trillion. This discrepancy highlights the challenges in astronomical observations and the importance of deep field surveys in improving our understanding of the universe's structure and evolution.

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Most relevant research papers on this topic

THE EVOLUTION OF GALAXY NUMBER DENSITY AT z < 8 AND ITS IMPLICATIONS

The total number of galaxies in the universe up to z = 8 is (2 trillion), a factor of 10 higher than would be seen in an all sky survey at Hubble Ultra-Deep Field depth, and this result resolves the Olbers' paradox.

Highly Cited

2016·

135citations

·C. Conselice et al.

Hydrodynamics, Vortices and Angular Momenta of Celestial Objects

Non-irrotational hydrodynamic flow in the universe can explain the formation of large numbers of galaxies and stars, indicating a primordial rotation broken up into vortex line structures.

2011·

58citations

·C. Sivaram et al.

How many galaxies are in the universe?

Galaxy in the Milky Way than in the Virgo cluster, and surveys are biased towards the Milky Way, making it harder to detect distant galaxies.

2016·

1citation

·Keith T. Smith

A large population of galaxies 9 to 12 billion years back in the history of the Universe

This survey reveals a large population of galaxies at 9-12 billion years back in the history of the Universe, 1.6 to 6.2 times larger than previous estimates, with vigorous star formation rates.

2005·

45citations

·O. Fèvre et al.

Galaxies as Gravitational Lenses

Gravitational lenses can produce distorted and amplified images of distant galaxies, allowing us to study their morphological configurations.

1968·

20citations

·J. Barnothy et al.

The size distribution of galaxies in the Sloan Digital Sky Survey

The size distribution of galaxies is well-defined by a log-normal function, with median being the median size for each type of galaxy.

Highly Cited

2003·

890citations

·S. Shen et al.

A common mass scale for satellite galaxies of the Milky Way

The Milky Way's satellite galaxies have a common mass of about 107 within their central 300 parsecs, indicating they are the most dark-matter-dominated galaxies known.

Highly Cited

2008·

434citations

·L. Strigari et al.

Our Universe

Our universe contains about two billion galaxies and 88 constellations, with Virgo being the second largest constellation in size and easily observed in the sky by humans.

2017·

59citations

·R. Petrescu et al.

Galaxy number counts — V. Ultradeep counts: the Herschel and Hubble Deep Fields

Simple Bruzual & Charlot evolutionary models with monotonically increasing star-formation rates fit the data to z 3, with internal dust absorption in spirals affecting the results.

Highly Cited

2000·

149citations

·Nigel Metcalfe et al.

The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: measurements of the growth of structure and expansion rate at z = 0.57 from anisotropic clustering

The anisotropic clustering of massive galaxies in the SDSS-III BOSS data release 9 sample suggests a cosmological expansion rate of 0.74 0.016 at z = 0.57, independent of the Universe's evolution at z 0.57.

Highly Cited

2012·

371citations

·B. Reid et al.

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