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Galaxy Structure

At a Glance: Galaxy Structure

All galaxies contain the same three things. What are they?

Galaxy Structure
Produced by the Space Telescope Science Institute’s Office of Public Outreach.
All images, illustrations, and videos courtesy of NASA, ESA, and STScI except:
·       NGC 6822 image courtesy of the Local Group Galaxies Survey Team/NOAO/AURA/NSF
·       Taurus constellation drawing from Firmamentum Sobiescianum sive Uranographia by Johannes Hevelius, courtesy of the United States Naval Observatory
·       NGC 4565 image courtesy of the European Southern Observatory
·       Small Magellanic Cloud image courtesy of F. Winkler/Middlebury College, the MCELS Team, and NOAO/AURA/NSF
Written by Vanessa Thomas
Designed by John Godfrey 
Music courtesy of Association Production Music


 at-a-GLANCE. The Makeup of Galaxies. 

A spiral galaxy on the left, distant star with hazy light surrounding it in the middle, random spread of stars and dust on the right.

All galaxies contain stars, gas, and dust. 

But the ways these contents are arranged, and the amounts of each, are different for each kind of galaxy. 

Spiral galaxy with bright star in the middle.

Spiral galaxies are defined by their large, swirling disks of gas, dust, and stars. 

The disk blazes with young stars but contains older stars as well. 

The compact core of a spiral galaxy smolders with the golden glow of much older stars. 

A spiral galaxy's halo contains a smaller population of ancient stars and star clusters that are often as old as the galaxy itself. 

Bright star surrounded by hazy light.

Elliptical galaxies are round or elongated clouds packed with ancient stars. 

Small elliptical galaxies contain just a few million stars, but giant ellipticals can contain over a trillion. 

Ellipticals usually have very little dust, but some have more than others. 

Young stars are rare in elliptical galaxies, but they can be found in ellipticals that have recently engulfed a galaxy with enough gas and dust to spark a bout of star formation. 

Random configuration of stars floats in bright pink dust and gas.

Irregular galaxies are messy blobs of gas, dust, and stars. 

These galaxies tend to be especially dusty and gassy. 

Dust and gas are the construction materials for new stars. 

Patches of young stars and star-forming regions often give irregulars a blotchy complexion.