You probably already know that the galaxy where our planet Earth and the entire Solar System exist is called the Milky Way. But did you know that our Milky Way is not alone in this vast cosmos?
To understand the composition and evolution of the universe, scientists have spent decades trying to uncover one fundamental mystery — how many galaxies actually exist in our universe? The final answer they reached was truly astonishing.
When we look up at the night sky, every single star visible to our eyes belongs to our very own Milky Way Galaxy. For centuries, humanity believed that the Milky Way was the only galaxy in existence — that our entire universe was just this one enormous island of stars.
But this belief changed dramatically in 1924, when astronomer Edwin Hubble made a discovery that forever reshaped our understanding of the cosmos. Using a powerful telescope, Hubble identified variable stars in several spiral nebulae. By calculating their distances, he realized something extraordinary — these nebulae were far too distant to be part of the Milky Way. They were, in fact, entire galaxies of their own. From that moment, humanity understood that the universe is filled with countless galaxies.
In 1995, NASA made the first reliable estimate of how many galaxies might exist. Scientists pointed the Hubble Space Telescope toward a tiny, seemingly empty region in the constellation Ursa Major and observed it continuously for ten days. This area was just one twenty-four-millionth of the entire sky — yet in that small patch, the telescope captured over 3,000 galaxies. This image became famous as the Hubble Deep Field.
Later, in 2003 and 2004, astronomers repeated the experiment with an even deeper focus — the Hubble Ultra Deep Field. They combined images taken over ten years, capturing light from ultraviolet, visible, and infrared wavelengths. The result was astonishing: more than 5,500 galaxies in that single small region of space. Scientists then realized that if so many galaxies exist in such a tiny portion of the sky, our entire observable universe must contain hundreds of billions of them.
In 2016, researchers estimated that there could be around two trillion galaxies in the observable universe. But NASA’s New Horizons mission data from 2021 provided a more refined number — roughly 200 billion galaxies that we can currently observe. And yet, this remains only an estimate, because this number includes only the galaxies whose light has managed to reach us since the birth of the universe.
Beyond that visible horizon lies an unknown realm — regions of space whose light hasn’t yet reached Earth and possibly never will, because the universe itself is expanding faster than light can travel. Those galaxies are forever beyond our view. We know they exist, but we may never be able to see them.
According to current estimates, there are about 200 billion galaxies in our observable universe. But astronomers believe that this number might actually be ten times smaller than the true total. The reason is that even our most powerful telescopes can detect only about ten percent of the galaxies that truly exist. The rest are either too faint or too distant to be observed.
Using advanced simulations, scientists found that in the early universe, the density of galaxies was almost ten times higher than it is today. Most of them were small, dim, and lightweight — possibly similar to the satellite galaxies that orbit the Milky Way today. Over billions of years, many of these small galaxies merged together to form larger ones, reducing their total number but increasing their size and mass. This means that the galaxies we see today are the evolved survivors of countless cosmic mergers.
The truth is that we have barely scratched the surface. We still know only a small fraction — perhaps just ten percent — of all galaxies that actually exist. But that is beginning to change. With the James Webb Space Telescope, our window into the deep cosmos has opened wider than ever before. This next-generation telescope is already capturing light from the earliest galaxies formed after the Big Bang — light that has traveled for more than 13 billion years.
In the coming years, Webb will not only help us answer our biggest questions about galaxy formation but also reveal mysteries we haven’t even imagined yet. The universe is vast, and our journey to understand it has only just begun.