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.

2012 December 17
See Explanation.  Clicking on the picture will download 
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NGC 922: Collisional Ring Galaxy
Image Credit: NASA, ESA; Acknowledgement: Nick Rose

Explanation: Why does this galaxy have so many big black holes? No one is sure. What is sure is that NGC 922 is a ring galaxy created by the collision of a large and small galaxy about 300 million years ago. Like a rock thrown into a pond, the ancient collision sent ripples of high density gas out from the impact point near the center that partly condensed into stars. Pictured above is NGC 922 with its beautifully complex ring along the left side, as imaged recently by the Hubble Space Telescope. Observations of NGC 922 with the Chandra X-ray Observatory, however, show several glowing X-ray knots that are likely large black holes. The high number of massive black holes was somewhat surprising as the gas composition in NGC 922 -- rich in heavy elements -- should have discouraged almost anything so massive from forming. Research is sure to continue. NGC 922 spans about 75,000 light years, lies about 150 million light years away, and can be seen with a small telescope toward the constellation of the furnace (Fornax).

Tomorrow's picture: icy sun pillar

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