How many galaxies are there in the universe? Thousands? Millions? More? These are questions that astronomers revise every few years. They periodically count galaxies using advanced telescopes and techniques. Whenever they do a new galactic census, they find that there are more of these "star cities" than they think.
The number of galaxies in the universe
So, how many? Some studies that are done using the Hubble Space Telescope showed that there are hundreds of billions of galaxies in the universe. However, observations show it can be up to 2 trillion. The fact is that the universe is larger than astronomers think.
Yes, there are hundreds of billions of galaxies and the universe is huge. However, the more interesting thing is that, today there are actually fewer galaxies in the universe than before. This may sound pretty weird. So what happened to the rest? The answer lies in the term "merging." Galaxies merge with each other to form larger galaxies over time. Therefore, many of the galaxies we see today are those that have survived billions of years of merging.
The history of the universe
At a time when the 19th century turned to the 20th, astronomers thought that one galaxy, our Milky Way, was the sole universe. But in the sky, they saw other strange, horrible things that they called "spiral nebula." However they never realized that these could be another, very distant galaxies.
The astronomer Edwin Hubble's discovery of "spiral nebula" in the 1920s, changed everything. He developed a variant of the "variable star" technique developed by Henrietta Leavitt and used it to measure the distance to stars. He found that the nebula he saw was outside our galaxy. It was farther than any star in our galaxy. This showed him that the spiral nebula we know today as the Andromeda Galaxy is not part of the Milky Way. It was a completely different galaxy. With this important observation, the number of known galaxies has doubled. Astronomers began to compete to find more and more galaxies.
Today, astronomers are able to see even more distant galaxies. Everywhere in the universe is full of galaxies, irregular spheres of light, spirals, and ellipticals. As the astronomers observed the galaxies, they learned how they merged. So they realized that our own Milky Way and Andromeda would also merge in the distant future.
Astronomers have discovered many more galaxies thanks to advanced telescopes compared to Hubble's time. They started counting the galaxies periodically. With the latest census taking at the Hubble Space Telescope and other observatories, more galaxies continue to be found at greater distances. But even though they discover more galaxies, astronomers can only see 10 percent of the galaxies they know are there. But why?
There are many galaxies that cannot be seen or detected by today's telescopes and techniques. 90 percent of the galaxy census falls into this "invisible galaxies" category. With newer solutions like the James Webb Space Telescope, they will eventually be detected. This telescope will be able to see their lights (many of them are very faded and are in the infrared part of the spectrum)
Less galaxy means less light
While the universe has at least 2 trillion galaxies, the fact that it had more galaxies in its early years may shed light on a question that astronomers wonder: If there are stars that emit so much light in the universe, why is the sky dark at night? This question is known as Olbers' Paradox (named after the German astronomer Heinrich Olbers who first asked this question).
The answer lies in the "lost" galaxies. The light of the stars coming from the farthest and oldest galaxies may not be visible to us due to the redness of light because of the expansion of space, the dynamic nature of universe, and the absorption of light by intergalactic dust and gas. If you combine these factors with other details that reduce our ability to detect visible and ultraviolet (and infrared) light in the farthest galaxies, it becomes clear why the sky appears dark at night.
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