Scientists Say: Galaxy

These stellar groups can contain millions to billions of stars

This is a colorized image of the galaxy Andromeda. Andromeda is a spiral galaxy that neighbors the Earth’s home galaxy, the Milky Way. 

JPL-Caltech/NASA

Galaxy (noun, “GAAH-lex-ee”)

This word describes an enormous collection of stars bound together by gravity. Galaxies typically contain millions to trillions of stars, plus gas, dust and leftovers from star explosions. Scientists estimate that there are at least two trillion galaxies in the part of the universe that can be observed from Earth.

Galaxies come in lots of different shapes. Our home galaxy, the Milky Way, is a spiral galaxy. These galaxies often look like pinwheels. Elliptical galaxies are fuzzy ovals. Some galaxies are called “irregular” because they lack symmetry and can look like a bunch of blobs. Gravity also pulls galaxies together into groups called clusters. These clusters can include just a couple of galaxies or up to thousands. Really big clusters can be tens of millions of light years across or even larger.  

In some galaxies, new stars continue to form. Other galaxies have settled down and haven’t seen a new star for billions of years. At the center of many galaxies are black holes, where gravity is so strong that not even light can escape. Earlier this year, scientists got a picture of a supermassive black hole in the center of the M87 galaxy. The M87 galaxy is located in the constellation Virgo.

In a sentence

A 3-D map of stars shows that the Milky Way looks like a deformed potato chip.

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Carolyn Wilke is a staff writer at Science News for Students. She has a Ph.D. in environmental engineering. Carolyn enjoys writing about chemistry, microbes and the environment. She also loves playing with her cat.

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