How many galaxies are there in the known universe
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The Number of Galaxies in the Known Universe
Estimations of Galaxy Count
Estimating the number of galaxies in the known universe is a complex task due to the limitations and biases of astronomical surveys. However, current observational evidence suggests that there are approximately 100 billion galaxies in the observable universe1 7. This estimation is based on deep-field observations and large-scale surveys such as the Hubble eXtreme Deep Field and the Sloan Digital Sky Survey (SDSS)1 9.
Deep-Field Observations
Deep-field observations, like those from the Hubble Space Telescope, have been instrumental in identifying distant galaxies. These observations reveal that the universe contains a vast number of galaxies, many of which are faint and distant, making them difficult to detect with less sensitive instruments1. The Hubble eXtreme Deep Field, for instance, has provided a glimpse into the universe's distant past, showcasing a multitude of galaxies at various stages of evolution1.
Large-Scale Surveys
Large-scale surveys such as the SDSS have cataloged millions of galaxies, providing a more comprehensive view of the universe's structure. The SDSS, for example, has compiled a list of over one million galaxies, classified into different morphological types such as spirals, ellipticals, and irregulars9. These surveys help refine our understanding of the number and types of galaxies present in the universe.
Evolution of Galaxy Estimates
The number of galaxies estimated to exist in the universe has evolved over time. Early estimates were significantly lower due to the limitations of observational technology. However, as telescopes and detection methods have improved, the estimated number of galaxies has increased. For instance, a flux-limited I-band survey of galaxies at look-back times of 9 to 12 billion years found a population of galaxies 1.6 to 6.2 times larger than previous estimates, indicating that earlier counts were likely underestimations2.
Conclusion
In summary, the current consensus among astronomers is that there are approximately 100 billion galaxies in the observable universe. This number is derived from deep-field observations and large-scale surveys, which have significantly improved our ability to detect and catalog galaxies. As observational technologies continue to advance, our understanding of the universe's structure and the number of galaxies it contains will likely become even more refined.
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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.
A large population of galaxies 9 to 12 billion years back in the history of the Universe
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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 CitedA common mass scale for satellite galaxies of the Milky Way
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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.
Gamma-Ray Emission of Active Galaxies
The observable universe consists of billions of galaxies, many of them containing 100 billion or more stars, like our “Milky Way” for example. On a morphological basis these galaxies are grouped into three main categories: spirals, ellipticals, and irregulars.
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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 CitedThe 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.
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