How many galaxies are there

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How Many Galaxies Are There in the Universe?

Estimating the Number of Galaxies

Estimating the number of galaxies in the universe is a complex task due to the limitations and biases of astronomical surveys. The Hubble eXtreme Deep Field (XDF) image, one of the deepest images of the universe ever taken, reveals thousands of galaxies in a tiny patch of sky, suggesting a vast number of galaxies across the entire sky .

Current Estimates

Current observational evidence suggests that there are about 100 billion galaxies in the observable universe . This estimate is based on deep-field observations and extrapolations from smaller, more detailed surveys.

Challenges in Counting Galaxies

One of the main challenges in counting galaxies is that many galaxies are faint and distant, making them difficult to detect with current technology. Surveys like the Sloan Digital Sky Survey (SDSS) have cataloged over a million galaxies, providing a significant sample for statistical analysis . However, even with such extensive surveys, many galaxies remain undetected due to their faintness or because they are obscured by dust and gas .

Evolution and Distribution of Galaxies

Understanding the number of galaxies also involves studying their distribution and evolution over time. For instance, a survey of galaxies 9 to 12 billion years ago found a population 1.6 to 6.2 times larger than previous estimates, indicating that the number of galaxies has changed significantly over cosmic time .

Local Group and Nearby Galaxies

Closer to home, within 10 megaparsecs (Mpc) of the Milky Way, there are 179 known galaxies, forming the Local Group and several other nearby groups . This local census helps astronomers understand the distribution and types of galaxies in our immediate cosmic neighborhood.

Conclusion

In summary, while the exact number of galaxies in the universe is still uncertain, current estimates suggest there are about 100 billion galaxies. This number is based on deep-field observations and extensive surveys, though many galaxies remain undetected due to their faintness or other observational challenges. Understanding the number and distribution of galaxies is crucial for studying the evolution of the universe and the formation of cosmic structures.

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Most relevant research papers on this topic

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

Science

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. Fèvreet al.

Nature

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. Shenet al.

Monthly Notices of the Royal Astronomical Society

On the true shapes of galaxies

The APM Bright Galaxy Survey provides accurate measurements of image characteristics, enabling us to infer the true shapes of galaxies using oblate, prolate, and triaxial models.

Highly Cited

1992·

120citations

·D. Lambaset al.

Monthly Notices of the Royal Astronomical Society

Galaxy evolution. Galaxy zoo volunteers share pain and glory of research.

Galaxy Zoo volunteers have classified the Sloan Digital Sky Survey's 1 million galaxies, bringing real statistical rigor to galaxy evolution research and revealing new astronomical objects.

Highly Cited

2011·

96citations

·D. Clery

Science

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. Sivaramet al.

arXiv: General Physics

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. Petrescuet al.

A Catalogue of Galaxies within 10 MPC

The catalogue contains 179 galaxies within 10 Mpc, with a near-complete listing for brighter galaxies, but also contains many significantly fainter ones.

Highly Cited

1979·

86citations

·R. Kraan-Korteweget al.

Astronomische Nachrichten

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. Reidet al.

Monthly Notices of the Royal Astronomical Society

Systematic properties of compact groups of galaxies.

Compact groups of galaxies contain fewer spirals and a deficiency of faint galaxies, with implications for dynamical evolution.

Highly Cited

1982·

490citations

·P. Hickson

The Astrophysical Journal

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