Galaxies come in different shapes and sizes. For example, we live in a barred spiral galaxy called the Milky Way, which is considered a large object of its kind.
It takes a particle of light, that is, a photon, 100,000 years to fly from one end of our galaxy to the other. That is, the diameter of the Milky Way is about 100,000 light years, given that photons travel at the speed of light (300,000 km/s).
But our galaxy is one of many galaxies in the universe. How many are there actually?
Astronomers can only see a small part of the universe
At first glance it may be easy to answer the question about the number of galaxies in the universe, but this is far from the truth. First, even with the most powerful telescopes, astronomers can see only a small part of the universe, that is, this is a local region of the vast cosmos or observable universe.
Astrophysicist Kai Neuske of the European Space Agency explains that the observable universe is considered that part of space from which light has managed to reach telescopes.
Although the universe has been around for 13.8 billion years according to current estimates, it is larger than 13.8 billion light-years in any direction from us.
The fact is that the universe is constantly expanding, and at the early stage of its existence, when space was smaller, light acquired a significant acceleration. Therefore, the current size of the visible universe is about 46 billion light-years away from us in all directions.
According to Pamela Gay of the Planetary Science Institute in Arizona, US, astronomers can only see about 3% of the total size of the universe.
“We see a maximum of 3% of the universe,” said Pamela Gay Living Science.
Another problem arises when estimating the total number of galaxies. There are so many galaxies that scientists can only estimate their number based on what can be seen in the local universe.
Gay explains that astronomers look at a small part of space, count the number of galaxies in it, and then multiply that by the size of visible space.
On the other hand, the existence of galaxies with different masses and sizes makes the calculations more complicated. Some are ten times larger than the Milky Way, others ten times smaller. Therefore, astronomers determined the minimum mass of the galaxy in order to make more or less correct calculations.
How many galaxies are there in the visible universe?
Based on this, an average of 1 to 2 trillion galaxies have existed in the visible universe throughout history. It is believed that there were more galaxies in the early universe, so average estimates are given.
But these results were obtained based on data from the Webb Space Telescope, which is relatively close to Earth. This means that some of the light the telescope received came from sources other than galaxies.
As shown by data from NASA’s New Horizons spacecraft, which is now the most distant probe in the solar system and is not strongly affected by outside light, estimates of the number of galaxies vary.
This data allowed astronomers to discover that there are 100 to 200 billion galaxies in the visible universe. But scientists still leave the number of galaxies in the range of 100 billion to 2 trillion, because it is not yet possible to make more accurate calculations.
How many galaxies are there in the entire universe?
According to Gay, if we see 3% of the universe, we can multiply the presented number of galaxies by the rest of the universe to get the total number of galaxies in space.
But astronomers don’t know the true size of the universe, so any estimates will be very rough.
On the other hand, if the universe is infinite, then there are an infinite number of galaxies in it, scientists say.
