April 14, 2009
The universe does not repeat itself. Every sunrise is unique, every snowflake singular, and every birthday yours alone.
M101: The Pinwheel Galaxy
Birthday · April 14, 2009
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APOD published April 14, 2009. Credit: Adam Block, Mt. Lemmon SkyCenter, U. Arizona. A publication-date match, not a photo taken on your date. Independent of NASA.
Why do many galaxies appear as spirals? A striking example is M101, shown above, whose relatively close distance of about 27 million light years allows it to be studied in some detail. Recent evidence indicates that a close gravitational interaction with a neighboring galaxy created waves of high mass and condensed gas which continue to orbit the galaxy center. These waves compress existing gas and cause star formation. One result is that M101, also called the Pinwheel Galaxy, has several extremely bright star-forming regions (called HII regions) spread across its spiral arms. M101 is so large that its immense gravity distorts smaller nearby galaxies.
Image credit: Adam Block, Mt. Lemmon SkyCenter, U. Arizona