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Did you know that our solar system is part of a larger galaxy called the Milky Way? In fact, all the stars that are visible from Earth form part of the Milky Way galaxy. If it’s dark, usually far away from city lights, the Milky Way is visible as a beautiful band of stars scattered across the night sky. It is estimated to contain between 100 billion and 400 billion stars and is approximately 100,000 light-years across.
However, only a fraction of these billions of stars is visible from Earth. No matter where you look up in the world, you aren’t going to be able to see more than about 2,500 stars.
The Milky Way wasn’t always this large. Our galaxy got its size by consuming other galaxies! When galaxies meet, they don’t just smash into each other. They lose their shape and combine to form one large galaxy. Their supermassive black holes also eventually come together to form a single black hole at the center. In fact, our galaxy is currently consuming Canis Major Dwarf Galaxy – adding its stars to the collection of stars in the Milky Way.
Even with all those stars, some scientists are even more interested in what they can’t see. Scientists believe that around 90% of our galaxy consists of dark matter , which is invisible but has a large gravitational force. All the amazing things we can see only make up 10% of the mass of the Milky Way.
Our galaxy is only one of billions of galaxies in the universe. Galaxies come in different shapes and sizes. Some are spiral-shaped with stars in their arms. If viewed from above, these galaxies look like a pinwheel. Other galaxies are oval-shaped, called elliptical galaxies. There are also galaxies with irregular shapes that look like random blobs .
According to scientists, our galaxy has a warped spiral shape (almost like a large whirlpool) and rotates every 200 million years. If you wondered how our galaxy got its shape, you are not alone. This is a question that has baffled scientists for a long time. NASA recently discovered that spiral galaxies, like the Milky Way, are shaped by magnetic fields . These magnetic fields cannot be seen by human eyes. But with the help of measurements from the Hubble Space Telescope (HST), the Nuclear Spectroscopic Array (NuSTAR), and the Sloan Digital Sky Survey (SDSS), these magnetic fields can finally be observed.
In terms of size, our galaxy falls somewhere in the middle of the scale. The largest known galaxy (IC 1011) contains more than 100 trillion stars. Other large galaxies have around 1 trillion stars. Small galaxies are called dwarf galaxies and contain roughly 10 billion stars.
Many scientists believe that the Milky Way has a supermassive black hole in the middle called Sagittarius A*. (A* is a code scientists use for “A-star.”) Interestingly, scientists believe the gravity from this black hole might be what is holding our galaxy together. A black hole is born when a giant star runs out of energy. The star collapses, causing an explosion called a supernova. Its gravity (or attractive force) is so strong that it will pull in anything that comes close, even stars! Luckily the Earth is at least 25,000 light-years away from the center of our galaxy. We don’t have to worry about being swallowed by the black hole anytime soon.
Another fun fact is that Milky Way galaxy, along with everything else in the universe, is always moving through space. Within our solar system, the Moon orbits around the Earth and the Earth moves around the Sun. But it doesn’t stop there! The Sun also moves inside the Milky Way, and the Milky Way moves relative to the Cosmic Microwave Background (CMB) radiation. The CMD is a good reference point to determine how fast something is space is moving.
In terms of age, the Milky Way is roughly 13.6 billion years old! It also belongs to a cluster of at least 40 galaxies, called the Local Group. Although this might sound like a lot, if we expand out we find that the Local Group is part of an even bigger group known as the Virgo Supercluster , with around 100 galaxy groups.
The Andromeda galaxy is the closest galaxy to ours. But even this nearest neighbor is about two million light-years away. Scientists believe that the Andromeda and Milky Way galaxies will collide. Luckily for us, they don’t expect that to happen for the next five billion years.
Now that you know more about the Milky Way, see if you can spot it the next time you’re out on a clear night.
Flesch Kincaid Grade Level: 7.7
Flesch Kincaid reading ease score: 67.3
Black hole: A region in space where gravity is so strong that everything is pulled in and nothing can escape, not even light
Dark matter: Invisible mass in space that has gravity
Galaxy: a huge collection of stars, planets, dust, rocks, and gas in space, all held together by gravity
Hubble Space Telescope: the first big optical space observatory telescope
Cosmic Microwave Background: The radiation left over from the Big Bang
Light-year: the distance light travels in one year
Nuclear Spectroscopic Array: a space-based X-ray telescope
Magnetic fields: the area around a magnet that has magnetic force
Sloan Digital Sky Survey: a survey mapping one-quarter of the entire sky
Supercluster: galaxy groups on a large scale with diameters of thousands of light-years
Smith, Y. Shaping a Spiral Galaxy. Retrieved from https://www.nasa.gov/image-feature/shaping-a-spiral-galaxy-0
Royal Astronomical Society. “Black hole at center of Milky Way unpredictable and chaotic.” ScienceDaily. Retrieved from https://www.sciencedaily.com/releases/2022/01/220112094004.html
Pultarova, T. Tillman, N.T. Milky Way Galaxy: Facts about our galactic home. com. Retrieved from https://www.space.com/19915-milky-way-galaxy.html
Williams, M. 10 Interesting Facts About the Milky Way. com. Retrieved from https://www.universetoday.com/22285/facts-about-the-milky-way/