How many galaxies are there in the universe?

Our observable universe, which extends for tens of billions of light-years in all directions, contains an enormous number of galaxies within it.

Each galaxy contains a huge group of stars.

But have you ever wondered how many galaxies are there in the universe?

Counting and counting them seems to be an impossible task given the limitations of our tools.

According to an article on Big Think, the exact number of galaxies has been a mystery, with estimates rising from thousands to millions to billions, all with improved telescope technology.

And if we make the most accurate estimate using the best technology available today, we'll say there are 170 billion galaxies in our universe.

But we know it's much more than that, as recent estimates suggest there are two trillion galaxies in the universe.

Hubble deep field image

The strategy used by scientists to observe galaxies in the universe was to direct a telescope to stare for a long time at a specific empty spot of the sky where there are no known stars or galaxies.

The longer the telescope stares at that spot, the more light - from far away - it collects, and thus more galaxies are discovered in the universe.

Scientists did this for the first time in the mid-1990s using the Hubble Space Telescope, which focused on observing a specific patch of sky that was one out of 32 million parts of the sky, which was known to contain almost nothing.

By observing that tiny patch of sky, the Hubble eXtreme Deep Field (XDF) image was produced, which revealed a total of nearly 5,500 galaxies, representing the highest density of galaxies ever observed.

This was the best attempt by scientists to monitor the number of galaxies in the universe.

The next step was to estimate the number of galaxies in the entire universe, which is one way, as we take the part of the sky that the telescope imaged.

Then by using the ratio of the part of the sky imaged to the entire universe, you can determine the number of galaxies in the universe.

This same method of estimation can be followed, assuming that there is no significant cosmic variance, and that the universe is homogeneous.

The universe is homogeneous according to the cosmological principle that goes back to the general theory of relativity, says Mario Livio, an astrophysicist at the Space Telescope Science Institute in Baltimore, Maryland. For Albert Einstein.

Also, according to the US space agency "NASA" (NASA), if you look at the contents of the universe, it will appear almost the same everywhere and in every direction.

This means that matter in the universe is homogeneous, even when averaged over very large scales, and this is called the cosmological principle.

We can therefore estimate the number of galaxies in the universe by taking the figure we observed in the form of the Hubble Deep Field, i.e. 5,500 galaxies and multiplying it by the number of images we would need to cover the entire sky, which is 32 million, which will eventually result in 176 billion galaxies in the universe.

However, this is not a true estimate.

This is the bare minimum, as galaxies that are too faint, too small, or too close to other galaxies are visible in this estimate.

Also, galaxies obscured by neutral gas and dust do not appear anywhere, and galaxies outside the redshift capabilities of the Hubble telescope do not appear.

There are more than 10 times the number of galaxies that Hubble can see (Shutterstock)

Two trillion galaxies.. How?

Today, scientists estimate that there are more than 10 times the number of galaxies that Hubble can see, about two trillion galaxies within the observable universe.

But how was this number arrived at?

According to BigThink, the big ingredient we need to come up with a true estimate is how precisely structure forms in the universe.

If we could run a simulation that starts with the components that make up the universe, the right initial conditions that reflect our reality, and the right laws of physics that describe nature, we can simulate how the universe evolved.

Remarkably, when we look at simulations that best match the observed data, we get an estimate of the true number of galaxies in our observable universe, which is two trillion.

Our universe, which extends in all directions, contains a huge number of galaxies (Shutterstock)

When we compare this number with the number we obtained from the "Hubble Deep Field" image, we will find that more than 90% of the galaxies within our universe exceed the detection capabilities of even humanity's greatest observatory.

Livio says that astronomers will be more able to improve this number observed through the James Webb Space Telescope, as the Hubble Space Telescope can look at galaxies that formed about 450 million years after the Big Bang, while scientists expect Astronomers say they can look back 200 million years after the Big Bang through the James Webb Telescope.