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What is a Galaxy, Anyway?

© Dina Ely

Our solar system is inside a galaxy. We live in a galaxy called the "Milky Way" (just like the candy bar!). There are many galaxies within the universe.

Every galaxy is made up of stars, space dust, and gas. The combination can take on several unique shapes. One such shape is a "spiral". The stars, dust, and gas swirl around in perfect spiral form. The spirals seem to be made up of "arms" that swirl around a central point. Spiral galaxies are some of the most beautiful galaxies in space. Our own galaxy is spiral shaped!

There are three other types of galaxies: lenticular, elliptical, and irregular. Generally speaking, galaxy types that are not spiral or elliptical are considered irregular. Irregular galaxies have no defined shape and can be very small. Elliptical galaxies are shaped like eggs or footballs. Some of the largest galaxies in the universe are elliptical.

Galaxies range in size from a mere 1 million stars to 1 trillion stars. Our own galaxy packs an impressive 100 billion stars. Our galaxy gets its name from the light produced by all the stars inside it, which from Earth, looks like a band of milky-white light across the night sky.

There are two theories about how galaxies are formed. One theory is that swirling masses of space dust and gas collided and collapsed in the pull of gravity, coming together to form a galaxy. The other theory is that floating "clumps" of matter throughout the universe eventually met up with each other and formed galaxies.

Large galaxies frequently "eat" smaller galaxies. This means that when a smaller galaxy gets too close to a larger galaxy, the larger galaxy "sucks" the smaller galaxy in and the two become one. The Milky Way is in the process of eating a smaller neighbor galaxy right now!

Our solar system lies in an arm of the spiral Milky Way called the "Orion" arm. It gets its name from the particularly bright stars that make up the constellation Orion.

Galaxies can "die" when the stars inside them burn out. Like a light bulb, stars can only shine for so long. When the matter that supplies the stars the necessary fuel to burn brightly runs out, the stars fade into blackness. When all the stars of a galaxy are gone, that galaxy ceases to exist in space. (It may turn into other celestial objects, like a black hole, but that's another topic for another article!)

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