Number of galaxies in the universe
Pro Research Analysisby 
Searched over 200M research papers
Galaxy Number Estimates in the Observable Universe
Estimating the number of galaxies in the universe is a complex challenge due to observational limitations and the vastness of space. Early estimates, based on visible galaxies in deep sky surveys, suggested there were about 100 to 200 billion galaxies in the observable universe 68. However, more recent and comprehensive studies have significantly revised this number upward.
Advances in Deep Sky Surveys and Galaxy Counting
With the advent of deeper and more sensitive astronomical surveys, such as those using the Hubble Space Telescope, astronomers have been able to detect fainter and more distant galaxies. These surveys revealed that many galaxies are too faint or too small to be detected with previous technology, leading to underestimates in earlier counts 21. By analyzing galaxy stellar mass functions up to a redshift of z ≈ 8, researchers have determined that the total number of galaxies in the observable universe is closer to 2 trillion—almost ten times higher than what would be seen in even the deepest Hubble surveys 18.
Evolution of Galaxy Number Density Over Time
The number density of galaxies has changed over cosmic time. Studies show that the total number density of galaxies with masses greater than 10^6 solar masses decreases as the universe ages, following a trend where the number density is inversely proportional to the age of the universe . At higher mass thresholds, the number density actually increases with time, reflecting the growth and merging of galaxies as the universe evolves 139.
Typical Galaxy and Star Counts
A typical galaxy, such as the Milky Way, contains about 100 to 400 billion stars 578. Galaxies themselves vary widely in size, with dwarf galaxies containing as few as 10 million stars and giant galaxies containing up to a trillion stars . The observable universe, therefore, contains an unimaginable number of stars, given the trillions of galaxies it holds 68.
Implications and Ongoing Research
The realization that there are about 2 trillion galaxies in the observable universe has major implications for our understanding of cosmic evolution, the cosmic background light, and the distribution of matter in the universe . Many of these galaxies are faint and small, contributing to the cosmic background light and helping to resolve longstanding questions such as Olbers’ paradox—why the night sky is dark despite the vast number of stars .
Conclusion
Current research indicates that the observable universe contains approximately 2 trillion galaxies, a number much higher than earlier estimates. This dramatic increase is due to improved detection of faint and distant galaxies, and ongoing studies continue to refine our understanding of galaxy formation, evolution, and the large-scale structure of the cosmos 128.
Sources and full results
Most relevant research papers on this topic