People have been watching the celestial travel of our own Milky Way galaxy in the sky for thousands of years, but very few ever knew or understood the vast size and number of galaxies that exist.

Galaxies are huge spans of gas, dust, dark matter, and from a million to trillions of stars. Everything in a galaxy is bound by gravity. Each star in a galaxy is a sun and there are thousands of solar systems in every galaxy.

The idea of galaxies is almost too much for us to comprehend, especially because scientists are finding thousands of them out in the universe.

NGC 4414, a typical spiral galaxy

To give you an idea of the incredible size: we live in the Milky Way galaxy and our sun is only one of around 100-400 billion stars in our galaxy.

Galaxies are in constant motion and their shape can be influenced by their neighbor galaxies and they can even slam into them in a collision creating entirely new galaxies.

As galaxies move in the universe they cross the path of other galaxies and when they collide, the gases combine and head to the center which, in turn, causes rapid star formation.

Almost all of the larger galaxies have a supermassive black hole at the center, and planetary scientists think that black holes may have something to do with the formation of a galaxy.

Our Milky Way galaxy has a supermassive black hole that has been named “Sagittarius A*,” and it has the mass of 4 million suns.

A study in 2016 resulted in an estimate that the observable universe has 2 trillion galaxies!  That would be 2 million million!  As scientists continue the exploration into ours and other galaxies, they are finding that some are very much like our Milky Way galaxy, and some are completely different.

Galaxy Statistics:

As we continue to study galaxies we are finding that some are completely on their own, are in pairs, or belong to larger galaxy associations that are called “groups, clusters, and superclusters.”

An example of this organization can be seen with our own Milky Way galaxy. It’s in a Local Group, which is a group of galaxies that span across 10 million light-years.

We have other galaxies in our Local Group, including the Andromeda galaxy and its satellites.

Along with the Local Group we have a neighboring galaxy cluster called the Virgo Cluster, and both of us are part of the bigger Virgo Supercluster. All of these galaxies have an expansion distance of about 100 million light-years across.

But it doesn’t stop there….the Virgo Supercluster is part of an even bigger supercluster called Laniakea, and it contains 100,000 galaxies.

If your head is spinning with the idea of all of those incredible numbers, you aren’t alone. The idea of galaxy sizes is pretty astounding.

Galaxy Types:

It wasn’t until the 20th century that we recognized the existence of any galaxy other than the Milky Way.

Some of the earliest astronomers guessed that there were others out in the universe, but since they seemed to look like fuzzy clouds, they just called them “nebulae.”

At 2.5 million light-years away, the Andromeda galaxy is our close neighbor and can be seen with the naked eye.

It wasn’t until the 1920s that Edwin Hubble identified that the Andromeda “nebula” was indeed a galaxy and from that time on scientists have been looking and studying for more information.

Once astronomers realized that there were so many galaxies of different shapes and sizes, they began to classify them.

It was Edward Hubble that created the classifications in 1936. He grouped galaxies into four main types: spiral galaxies, lenticular galaxies, elliptical galaxies, and irregular galaxies in the Northern Hemisphere.

Spiral Galaxies:

A majority of the observed galaxies fall into this class with around 2/3 of the known galaxies.

A spiral galaxy can be identified as a spinning, flat disk with spiral arms and a bulge in the center. The spinning is at hundreds of kilometers per second and this may be what causes the disk to look like a spiral.

Out Milky Way galaxy is a spiral galaxy and it has a center area with a starry bar.

Lenticular Galaxies:

These galaxies are called “lenticular” because they look more like lenses. They have a thinner, rotating disk of stars and also have a middle bulge, but no spiral arms.

They share characteristics with elliptical galaxies in that they have very little interstellar matter or dust. Lenticular galaxies seem to exist in some of space’s more densely populated areas.

Elliptical Galaxies:

These galaxies are usually round but they can actually stretch out longer on one of their axis so that they can appear like a cigar.

From our observations it seems that the biggest known galaxies in the universe are elliptical galaxies and they can extend out over two million light-years, holding up to a trillion stars.

But not all elliptical galaxies are huge, some can be smaller and those are called dwarf elliptical galaxies.

One of the characteristics of elliptical galaxies is that they contain very little dust or other interstellar matter and their stars are older.

Like spiral galaxies, their stars seem to orbit close to the center, but are more random and less organized.

You will find very few new stars being created in elliptical galaxies and this type of galaxy is commonly found in galaxy clusters.

Irregular Galaxies:

Galaxies that don’t fall into the three classifications of spiral, lenticular, or elliptical are referred to as “irregular galaxies.”

Many of these lack a distinct form and are often misshapen. It’s believed that their lack of specific shape is due to being influenced by other galaxies that are close to them.

Irregular galaxies are filled with dust and gas and due to this fact, they are perfect as star nurseries.

Origin of Galaxies:

Scientists believe that the Big Bang occurred 13.8 billion years ago and started the beginning of the universe.

180 million years later the first stars began to ignite and when the universe turned nearing 400 million years old, gravity began to pull and push galaxies into shape.

Scientists still aren’t completely sure how the galaxies formed. There are some theories that say that the galaxies were created from smaller clusters, called globular clusters that contained around one million stars.

Other theories indicate that the galaxies were created first and then the globular clusters came along.
Astronomers are also unsure which stars were created with the gases from their own galaxies versus being created as they crashed into other galaxies.


From a scientific standpoint, the time after the Big Bang, the universe was made up of subatomic particles and radiation.

The various theories on the creation of the galaxies remains unclear and is kind of a “chicken and egg” question.

Once galaxies are created they aren’t sitting still. The process of creating galaxies is still happening today as we watch galaxies collide and merge to make new galaxies.

Our nearest galactic neighbor of Andromeda is moving towards our Milky Way galaxy. It’s believed that billions of years from now the two galaxies will collide and create a new galaxy.


Nearly all galaxies, with only a few exceptions, sit in the middle of huge haloes of dark matter.

Scientists have created theoretical models that show that huge tendrils of this dark matter allowed normal matter to have a gravitational beginning in the early universe so that it could create the original galaxies.

The deduction of dark matter occurred when scientists studied galaxies and saw that the stars located in the outer areas of the galactic center were orbiting just as fast as the starts that were located further in.

This is a direct violation of Newton’s laws of gravity. The scientists decided that there was some other kind of matter other than clouds of gas, dust, and stars that made up the galaxy content; and to have this great of a gravitational effect, there had to be a lot of it.

Their calculations resulted in finding out that dark matter makes up five times more matter and its gravitational pull is the only way to detect it.


Thanks to a lot of new highly powered telescopes, scientists can study galaxies that are at a far distance.

They watch the stars that exist in the outer parts that orbit their galactic centers as well as those areas that are filled with dust and gas that act as star nurseries for the birth of new stars.

The Local Group is just one of many galaxy clusters and when observing them, scientists noted that they are all moving away from each other, creating more space between them.

This led to the understanding that the universe is expanding and that discovery led to the Big Bang theory.

The previous assumption was that the gravitational attraction of all that is in the universe would slow down the expansion rate and possibly stop or reverse it.

It was in the 1990s that scientists found out that the universe is actually moving faster in expansion and they believe that a force called “dark energy” is responsible for the acceleration.

Galaxy cluster

Scientists don’t have any idea what dark energy is but they have a theory that it’s energy that is held in the very vacuum of space.

Scientists have been able to calculate that this mysterious dark energy makes up about 68% of everything in the universe.

This led to the mathematical concept that 27% is dark matter, and only 5% remains for neutrons, protons, electrons, photons, and all else.

There is a calculation that shows that in the observable universe, there are at least 100 billion galaxies, and every one of them is filled with stars and solar systems.

When a diagram is drawn of the universe it looks like a bubbly structure with huge sheet and filaments of galaxies that are surrounded by gigantic voids or emptiness.

Scientists have designed a computer model called the Millennium Simulation, to try to understand how the galaxy formed and its structure.

The models show that dark matter merges and clumps together and acts as a scaffolding for the forming of galaxies and stars.

As the dark matter clumps and then is drawn to other clumps it creates a build-up of large systems that are followed by the creation of stars from the dust and gas.

The interaction of dark matter with galaxies and stars created the galaxies of today and they are organized into what is known as “The Hubble Sequence of Galaxies.”

Interesting Information:

Space is so incredibly large that when galaxies collide with each other it is rare that there stars do as well. This is good news for the Milky Way galaxy which may be colliding with the Andromeda galaxy!

Exploration and Study:

  • The vastness of space doesn’t allow fast travel. Thus far, only 5 robotic spacecraft have good enough speed to escape our solar system and head into interstellar space. Only NASA’s Voyager 1 has crossed the boundary so far, as it moved into interstellar space in 2012. Voyager 2 will be next. Both of the spacecraft remain in contact with NASA’s Deep Space Network.
  • In 2015, NASA’s New Horizon spacecraft went by Pluto and is exploring the Kuiper Belt. It will eventually leave our solar system along with the Pioneer 10 and 11 spacecraft.
  • The James Webb Space Telescope has empower scientists to view galaxies far back time. The constant research is designed to help us understand how galaxies evolved and are growing as well as gather data on star types that existed in the young galaxies. The study of hundreds or possibly thousands of galaxies are assisting scientists in understanding the way that elements heavier than hydrogen were created and built up to form galaxies.

Important Events:

 In 1983 a team observed a disc around Beta Pictoris that was thought to be planetary raw materials for the formation of a planet.

This was the first exoplanet evidence and 9 years later the first exoplanet was discovered. This event launched the continuing discovery of our solar system status.

These missions have enough velocity to take them outside of our solar system:

  • WISE/NEOWISE: 2009: WISE has accomplished scans of the total celestial sky 1.5 times. It has captured and sent back over 2.7 million images of space objects that range from galaxies to comets and asteroids that are close to Earth.
  • IBEX (Interstellar Boundary Explorer) 2008: IBEX will be detecting our solar system’s edge.
  • New Horizons: 2006: New Horizons is the first spacecraft to do an up close exploration near Pluto as well as its five moons.
  • Spitzer Space Telescope: 2003: Using ultra-sensitive infrared, the telescope studies comets, planets, asteroids, and distant galaxies.
  • Hubble Space Telescope: 1990: The Hubble was designed to get clear images of the deep and distant galaxies, stars, and most of our solar system’s planets.
  • Voyager 1: 1977: Voyager 1 was designed to fly by both Jupiter and Saturn and then continue to the outer reaches of our solar system.
  • Voyager 2: 1977: Voyager 2 is the only spacecraft thus far that has studied all of the four giant planets in our solar system at close range.

Pop Culture:

There have been too many references to galaxies in science, entertainment, movies, television, and books to mention.

However, the most notable may have occurred in the opening scene of the 1980 film Star Wars –  Empire Strikes Back with its iconic:

“A long time ago….in a galaxy far far away….”

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