How many galaxies are there in universe
Pro Research Analysisby 
Searched over 200M research papers
How Many Galaxies Are There in the Universe?
Estimating the Number of Galaxies: Challenges and Methods
Estimating the number of galaxies in the universe is a complex task due to the limitations and biases inherent in astronomical surveys. These surveys often miss galaxies that are faint or obscured by dust and gas, leading to incomplete data. Additionally, the methods used to identify galaxies, such as their optical colors, can leave out significant populations that do not fit expected patterns.
Observational Evidence and Estimates
Current observational evidence suggests that there are about 100 billion galaxies in the observable universe, each containing roughly 100 billion stars on average . This estimate is based on deep-field observations and large-scale surveys like the Sloan Digital Sky Survey (SDSS), which provide a statistical basis for understanding galaxy distribution and density.
Historical and Recent Discoveries
Historically, the understanding that our Milky Way is just one of many galaxies is relatively recent, dating back less than 100 years. Modern telescopes and deep-field surveys, such as the Hubble eXtreme Deep Field, have significantly expanded our knowledge, revealing billions of galaxies that were previously undetected.
Evolution of Galaxy Number Density
The number density of galaxies has evolved over time. Studies show that the total number of galaxies in the universe up to a redshift of 8 is approximately 2 trillion, which is almost ten times higher than what would be observed in an all-sky survey at Hubble Ultra-Deep Field depth. This suggests that many galaxies are faint and not easily detectable with current technology.
Implications for Galaxy Evolution and Cosmology
The discovery of a larger number of galaxies than previously estimated has significant implications for our understanding of galaxy evolution and cosmology. It affects models of star formation rates and the distribution of baryonic matter in the universe . Additionally, it helps explain phenomena such as the cosmic background light and Olbers' paradox, which questions why the night sky is dark despite the vast number of stars.
Conclusion
In summary, while traditional estimates placed the number of galaxies in the observable universe at around 100 billion, recent studies suggest that the actual number could be as high as 2 trillion. This discrepancy highlights the challenges in astronomical observations and the potential for future discoveries as technology advances. Understanding the true number of galaxies is crucial for refining our models of the universe and its evolution.
Sources and full results
Most relevant research papers on this topic