How many galaxies
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How Many Galaxies Are 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, provides a glimpse into the vast number of galaxies, but even this image is limited by the sensitivity and range of the telescope1.
Current Estimates
Current observational evidence suggests that there are about 100 billion galaxies in the observable universe8. This estimate is based on various deep-field observations and surveys, which have progressively improved our understanding of the universe's structure and content.
Historical and Modern Surveys
The Sloan Digital Sky Survey (SDSS) has been instrumental in studying the size distribution and other properties of galaxies. With a sample of about 140,000 galaxies, the SDSS provides highly accurate statistics that help refine our estimates of galaxy numbers and characteristics2. Additionally, the HyperLEDA database, which includes about one million confirmed galaxies, further supports these estimates by providing detailed data on galaxy positions, diameters, and other properties6.
Evolution Over Time
Understanding the number of galaxies also involves looking back in time. A study focusing on galaxies 9 to 12 billion years ago found a significantly larger population of galaxies than previously estimated, suggesting that the number of galaxies has evolved over time3. This study identified 970 galaxies with spectroscopic redshifts between 1.4 and 5, indicating vigorous star formation rates and a higher cosmic star formation rate than previously measured.
Local and Large-Scale Structures
On a more localized scale, our Milky Way is part of the Local Group, which contains about 40 galaxies. This group is part of larger structures like the Virgo Cluster, which has at least 1,300 catalogued members, and the Virgo Supercluster, which includes even more galaxies5. These structures illustrate the hierarchical nature of galaxy distribution in the universe.
Conclusion
In summary, while the exact number of galaxies in the universe is still a subject of research and refinement, current estimates suggest there are about 100 billion galaxies in the observable universe. This number is supported by various surveys and databases, and it evolves as our observational techniques and technologies improve. Understanding the distribution and evolution of galaxies remains a key area of study in astronomy.
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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.
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 CitedA 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.
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 CitedOn the Distribution of Galaxies.
The Local Group is a large group of galaxies, with most of them in two sub-clumps, and most of them are in the Supergalactic Plane, a band around the sky passing through Virgo.
Hyperleda. I. Identification and designation of galaxies
The new HYPERLEDA database provides accurate coordinates, diameter, axis ratio, and position angle for over one million galaxies, with improved compatibility between NED, SIMBAD, and LEDA.
Highly CitedThe 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.
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