A galaxy is a very large entity in space made up of gas, dust, rock, matter, and stars. It is completely held together by the power of gravity. Some galaxies have several hundred billion stars in them.
The germ galaxy relates back to the Hellenistic Greek word ‘γαλαξίας’ (which means “milky”). The word itself is a shortened version of “γαλαξίας κύκλος,” which means ‘milky circle.’ This makes sense when seeing that our galaxy is called the “Milky Way.”
An easy way to think about a galaxy is to think of it as a galactic neighborhood. It is a community floating in space that contains the materials needed to exist and evolve (such as stars, gas, matter, and movement).
How is a Galaxy Made?
Astronomers are still studying how galaxies are made, but our telescopes have helped them form an idea about galaxy formation. Some astronomers believe that galaxies are made as gas and dust pull together to create stars as areas of space collapse and fall inward. Many astronomers have a different idea, which comes from observations of space through the Hubble Telescope.
Many astronomers believe that there are small pockets in the universe where matter begins to collect gas and dust over time. Once the pocket has enough matter, all the matter will be pulled towards a center and start to spin.
Some of these galaxies or newly-forming galaxies can crash into other galaxies, usually forming elliptical galaxies. Many galaxies are created through the merging of two to several galaxies.
When were Galaxies Created?
The very first galaxies mostly likely formed nearly several million to a billion years after the Big Bang. However, galaxies are forming all the time. Galaxies are constantly running into each other to form new ones.
In 2016, NASA believed they found the oldest galaxy yet. The galaxy, called GN-z11, is 13.4 billion light-years away, and it is believed to have formed 400 million years after the Big Bang.
How Many Galaxies are There?
While there is not an exact known amount, scientists estimate that there are over 100 billion galaxies in the observable universe: this means there more than 100 billion galaxies in just what we can see.
There could be even more beyond what we cannot see.
What are the Most Famous Galaxies in the Universe?
The Milky Way Galaxy is the most famous galaxy because it is the one in which we live. It is a barred spiral galaxy with four primary spiral arms. It is mostly flat, and most of the galaxy’s mass comes from dark matter that rests in its halo.
Another famous galaxy is the Andromeda galaxy. Perhaps this galaxy is well known because it is moving towards our own. At 2.5 million light years away, astronomers project that the Milky Way and Andromeda galaxies will collide in about 4 billion years. Astronomers recently found that Andromeda contains 26 possible black holes.
Messier 51, also called The Whirlpool Galaxy, is also well-known. Like the Milky Way, it is a spiral galaxy. This galaxy was discovered in 1773, and it is known for its beautifully long spiral arms.
What Types of Galaxies are There?
When astronomers categorize galaxies, they specifically group them by looks, or by a system called “optical morphology.” The classification system is called the Hubble Classification of Galaxies. The major types of galaxies include the following:
- These galaxies look elliptical. Some even look squashed or flattened.
- They do not rotate.
- The stars inside of them move randomly, which creates their long shapes.
- Stars travel away from the galaxies, but then they are pulled back by gravity.
- The faster the stars move, the flatter and longer the elliptical galaxy tends to be.
- Some elliptical galaxies are huge, and astronomers believe that two galaxies fused together to create the elliptical galaxy.
- Unlike spiral galaxies, elliptical galaxies have no disk.
- These galaxies have bulging center from which arms, gas, younger stars, and dust extend.
- These galaxies have a disk, which is the flat area around the central bulge where young stars and gas are contained
- These galaxies are further divided by how their spiral arms group together, the tightness of their spiraling, and the size of the bulge at the center.
- These galaxies rotate or spin, and their arms follow the spin.
- These are galaxies that are smaller in mass and size, and they are not very bright.
- Their shapes can be elliptical, spheroidal, or irregular.
- These are often found in galaxy clusters, acting as companions to larger galaxies.
- These are galaxies that do not fall under the previous three categories.
- They have no clear shape or structure
- They have a mixture of young and old stars
- They have no defined or standard size
Interesting Facts About Galaxies:
- The Milky Way galaxy is nearly 50,000 light-years in radius.
- The gas that helps create galaxies is called ‘primordial gas.’
- The Milky Way is part of a group of galaxies called the Local Group. The Local Group is just a small group in the larger Virgo Supercluster
- Scientists believe that black holes rest at the center of many galaxies.
- Dark matter, which is found in galaxies, is matter that we cannot see. It helps the formation of galaxies by affecting gravity and motion.
- The existence of galaxies was first established in 1924 by Edwin Hubble. He found the Andromeda galaxy. By seeing that galaxies far from us were moving away, Hubble realized that the universe was expanding.
- Galaxies give off lots of energy through visible light, infrared, ultraviolet light, and x-rays. Astronomers use radio astronomy to examine the different forms of energy that galaxies produce.
- The Hubble Classification of Galaxies is also called the “tuning fork diagram.”
- 75 percent of galaxies fall under the classification of spiral galaxies.
- 20 percent are classified as elliptical galaxies.
- Collisions between galaxies don’t usually destroy stars, but the collision results in the formations of many new stars.