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.

June 25, 1998
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NGC 4650A: Strange Galaxy and Dark Matter
Credit: Very Large Telescope Project, ESO

Explanation: This strangely distorted galaxy of stars is cataloged as NGC 4650A. It lies about 165 million light-years away in the southern constellation Centaurus. The complex system seems to have at least two parts, a flattened disk of stars with a dense, bright, central core and a sparse, sharply tilted ring of gas, dust and stars. Observations show that the stars in the disk and the stars and gas in the ring really do move in two different, nearly perpendicular planes, probably as the result of a past galaxy vs. galaxy collision. The observed motions within both disk and ring also indicate the presence of "dark matter" - an unseen source of gravity which influences the movement of this system's visible stars. Over the decades evidence that our Universe is largely composed of such dark matter has grown while the nature of dark matter has remained a profound astrophysical mystery. The picture was constructed from images made using part of the European Southern Observatory's (ESO) new Very Large Telescope system now undergoing its testing phase.

Tomorrow's picture: Gliese 876

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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.