The cosmos is so immensely huge, brimming with infinite galaxies that differ in size, pattern, and makeup. Researchers have spent many years trying to calculate the total number of galaxies, but because of our observing technology, we are able only to make reasonable conjectures.
With the help of advanced telescopes like the Hubble Space Telescope and the James Webb Space Telescope, astronomers have been able to refine their estimates significantly. While early calculations suggested there were around 100 billion galaxies, later research pushed this number to as high as 2 trillion. However, recent findings indicate that the actual number could be somewhere in between. So, how do astronomers estimate this number, and what challenges do they face?
Early Estimates: The Hubble Deep Field Observations
The very first endeavour to approximate the amount of galaxies in the universe was made by the Hubble Space Telescope in the 1990s. The experiment was carried out by the telescope, and it immersed itself into a minuscule, practically blank area of the sky that included 10 consecutive days of data, making it possible to see thousands of dim galaxies. This image bore the name of the Hubble Deep Field (HDF), and it was one of the least detailed images of the universe that had been taken up until then.
By extrapolating from this small patch of the sky to the entire observable universe, scientists estimated that there were at least 100 billion galaxies. However, this estimate was based on what was visible at the time and didn’t account for galaxies that were too faint or too far away to be detected.
Expanding the Estimate: The Two-Trillion-Galaxy Hypothesis
In 2016, astronomers using data from multiple deep-field observations—including the Hubble eXtreme Deep Field (XDF)—suggested that the number of galaxies could be 10 times higher than previously thought. A study led by Christopher Conselice estimated that the observable universe could contain up to 2 trillion galaxies.
This estimate was based on improved calculations that considered galaxies too faint to be seen by Hubble. The reasoning was that as we look further into the past, we might see galaxies that have since merged or faded over time. This study reinforced the idea that the universe was once filled with many more small galaxies that later combined to form larger ones.
How Do Scientists Count Galaxies
Astronomers cannot physically count every galaxy in the universe, so they rely on statistical methods to estimate the total number. The process generally involves:
Observing a Small Section of the Sky:
- Telescopes like Hubble or James Webb focus on a small, representative area of the universe and capture detailed images of galaxies.
Counting the Galaxies in That Area:
- Scientists analyze the image and count the number of galaxies visible.
Extrapolating to the Entire Sky:
- Since the universe is assumed to be homogeneous on a large scale, astronomers multiply the number of galaxies in the observed area by the total number of similar sections in the sky.
Challenges in Estimating the Total Number of Galaxies
While the observable universe has been estimated to contain between 100 billion and 2 trillion galaxies, the total number of galaxies in the entire universe could be far greater—or even infinite.
The Observable Universe vs. The Entire Universe
The observable universe is the portion of the cosmos from which light has had time to reach us since the Big Bang, about 13.8 billion years ago. Due to the universe’s ongoing expansion, the observable universe is about 93 billion light-years in diameter.
However, the actual universe could be much larger. Some theories even suggest it is infinite, meaning the number of galaxies could also be limitless.
Limitations of Telescopes
Even with cutting-edge instruments like James Webb, our ability to detect distant galaxies is still constrained by:
- The brightness of objects (fainter galaxies remain unseen).
- Cosmic dust that obscures distant light.
- The limitations of current imaging technology.
The Evolution of Galaxies
The number of galaxies is not static. Over billions of years, galaxies merge, evolve, and fade. Some smaller galaxies combine to form larger ones, and others become too faint to be detected. This means that estimates change depending on whether we are counting past galaxies, current galaxies, or potential future ones.
Conclusion
Current estimates put the number of galaxies in the observable universe at a range between 100 billion and 2 trillion. But the total number of galaxies in the whole universe remains unknown. If the universe is infinite, then the number of galaxies may also be infinite.
The more sensitive our observational capabilities become, the better we understand the structure of the universe. Future findings by James Webb and other space-based telescopes are very likely to sharpen these estimates and provide far greater insight into how galaxies form, evolve, and sculpt the universe.