If we made the most straightforward estimate using today’s best technology, we’d state there are 170 billion galaxies in our Universe. But we know more than that, and our modern estimate is even grander: two trillion galaxies.
Galaxies are huge clusters of stars that populate our universe. But how many galaxies are there? Counting them seems like an impossible task. Sheer numbers are a problem – once the count gets into the billions, it takes a while to do the addition.
Another problem is the limitations of our tools. To get the best view, a telescope must have a large aperture (the diameter of the primary mirror or lens) and be above the atmosphere to avoid distortion from Earth’s air.
Perhaps the most striking example of this fact is the Hubble eXtreme Deep Field (XDF), an image created by combining 10 years of Hubble Space Telescope photographs. According to NASA, the telescope observed a small speck in the sky for a total of 50 days during repeated visits.
If you hold your thumb at arm’s length to cover the moon, the XDF area would be about the size of a pinhead. Gathering faint light over many hours of observation, the XDF revealed thousands of galaxies, both near and very distant, making it the deepest image of the Universe ever taken at that time. So if that single little speck contains thousands, imagine how many more galaxies could be found elsewhere.
While different experts’ estimates vary, an acceptable range is between 100 and 200 billion galaxies, said Mario Livio, an astrophysicist at the Space Telescope Science Institute in Baltimore, Maryland. The James Webb Space Telescope is set to reveal even more information about early galaxies in the Universe.
What is Galaxy?
A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems. A galaxy is held together by gravity. Our galaxy, the Milky Way, also has a supermassive black hole in the middle.
A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. The word is derived from the Greek galaxias (γαλαξίας), literally ‘milky’, a reference to the Milky Way galaxy that contains the Solar System.
Galaxies, averaging an estimated 100 million stars, range in size from dwarfs with less than a hundred million (108) stars, to the largest galaxies known – supergiants with one hundred trillion (1014) stars, each orbiting its galaxy’s center of mass.
Galaxies are categorized according to their visual morphology as elliptical, spiral, or irregular. Many are thought to have supermassive black holes at their centers. The Milky Way’s central black hole, known as Sagittarius A*, has a mass four million times greater than the Sun.
As of March 2016, GN-z11 is the oldest and most distant galaxy observed. It has a comoving distance of 32 billion light-years from Earth and is seen as it existed just 400 million years after the Big Bang.
Largest galaxy ever discovered
The largest galaxy ever discovered in our universe is the supergiant elliptical galaxy known as IC 1101. This galaxy contains well over 100 trillion stars and spans over 5.5 million light-years across.
IC 1101 is about 50 times larger than our Milky Way and is about 1 billion light-years / 320 megaparsecs away from us.
How Many Galaxies are there in the Milky Way?
Our own Milky Way has a few satellite galaxies, very small galaxies gravitationally bound to larger ones. These small galaxies have been or will be integrated/devoured by their larger brethren.
The Milky Way has satellite galaxies such as the Large and Small Magellanic Clouds. There are about fifty galaxies in the Milky Way, the largest of which is the Large Magellanic Cloud. This satellite galaxy is only 14,000 light-years across.
The Large Magellanic Cloud can contain up to 10 billion stars. This small galaxy will collide with our Milky Way in about 2.4 billion years.
How Many Galaxies are there in the Universe 2020?
Currently, in 2020, it is estimated that there are about 2 trillion galaxies in the observable universe. Each galaxy is unique, ranging in size from 10,000 light-years to hundreds of light-years.
Galaxies have been classified into five categories: spiral galaxies, barred spiral galaxies, lenticular, elliptical, and irregular galaxies. Our Milky Way is a barred spiral galaxy.
Is the Milky Way a Large Galaxy?
The Milky Way is considered a medium-sized galaxy. It spans 105,700 light-years in diameter and may contain at least 100 billion planets and about 400 billion stars.
Well, if the Milky Way is an average galaxy, what does a giant galaxy look like? Well, it would like IC 1101, which is currently the largest galaxy ever discovered.
IC 1101 is more than 50 times larger than the Milky Way. It stretches for over 5.5 million light-years across. This galaxy may have trillions of stars and planets.
Would The Number of Galaxies Change?
Measurements of the universe’s expansion — by observing galaxies racing away from us — show that it’s about 13.82 billion years old. However, as the universe gets older and larger, the galaxies will move farther and farther from Earth. This makes them more difficult to see in telescopes.
The universe is expanding faster than the speed of light (which doesn’t violate Einstein’s speed limit since the expansion comes from the universe itself and not from objects traveling through the universe). In addition, the universe is accelerating in its expansion.
This is where the concept of the “observable universe” – the universe we can see – comes into play. In 1 trillion to 2 trillion years, that means there will be galaxies beyond what we can see from Earth.
“We can only see light from galaxies whose light has had enough time to reach us.” That doesn’t mean that’s all in the universe. Hence the definition of the observable universe.”
Galaxies also change over time. The Milky Way is on a collision course with the nearby Andromeda Galaxy, and the two will merge in about 4 billion years. Later, other galaxies in our Local Group—the galaxies closest to us—will eventually merge. Residents of this future galaxy would have a much darker universe to observe.
“Civilizations started back then, they had no evidence that there was a universe with 100 billion galaxies.” “You wouldn’t see the expansion. You probably wouldn’t be able to tell there was a Big Bang.”
How Many Universes Are There?
Since the universe is so vast and complex, one might assume that other universes exist. There is only one universe that we currently know, and that is the universe we already live in.
The existence of other universes certainly seems possible; However, we are still in the process of studying our own before looking for others.
We know too little about our own universe, and decoding it is key to finding out if there are other universes out there.
Did you Know?
- Our sun takes about 250 million years to orbit the Milky Way. This means that the sun has already made about 20 orbits around the galaxy since its birth.
- We all orbit a black hole, the one at the galactic center of the Milky Way called Sagittarius A*.
- The Milky Way is thought to have about two rogue planets for each star. They are planets thrown out of their solar system. This can happen through collisions or if their sun went through a stellar evolution and they lost control.
- The outermost regions of the Milky Way indicate that it has not experienced any mergers with large galaxies in the past 10 billion years.
- The Sombrero galaxy is one of the most massive objects in the Virgo galaxy cluster. It has about 100 billion stars and is about 31.1 million light years / 9.55 megaparsecs from our solar system. This galaxy is about 49,000 light-years across, which is 30% the size of our Milky Way.
- Galaxies such as the Sombrero Galaxy demonstrate that the size of a galaxy does not necessarily produce more or fewer stars.