Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

July 2, 1995

The Cartwheel Galaxy
Picture Credit: NASA, Hubble Space Telescope

Explanation: The Cartwheel Galaxy shows a ring that is the result of a collision between a small and a large galaxy. After a small galaxy has moved through a big galaxy - in this case one that probably resembled our own Milky Way - a star formation wave moves out from the impact point like ripples across the surface of a pond. When galaxies collide it is rare that any two stars actually collide. Gravity, however, causes density waves to move out through the galaxy which in turn triggers the formation of hot, bright young stars, producing the ring that we see in this picture.

For more information see NASA, Hubble Space Telescope Scientific Institute press release.

Tomorrow's picture: The Great Nebula in Orion

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
&: Michigan Tech. U.