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.

2005 September 1
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One-Armed Spiral Galaxy NGC 4725
Credit: R. Kennicutt (Univ. Arizona), SINGS Team, JPL-Caltech, NASA

Explanation: While most spiral galaxies, including our own Milky Way, have two or more spiral arms, peculiar galaxy NGC 4725 has only one. In this false-color Spitzer Space Telescope infrared image, the galaxy's solo spira mirabilis is seen in red, highlighting the emission from dust clouds warmed by newborn stars. The blue color is light from NGC 4725's population of old stars. Also sporting a prominent ring and a central bar, this galaxy is over 100 thousand light-years across and lies 41 million light-years away in the well-groomed constellation Coma Berenices. Computer simulations of the formation of single spiral arms suggest that they can be either leading or trailing arms with respect to a galaxy's overall rotation.

Tomorrow's picture: X-ray Friday

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