The Polar Ring Galaxy NGC 4650A

The Polar Ring Galaxy NGC 4650A
From the Hubble Space Telescope
Located about 130 million light-years away, NGC 4650A is one of only 100 known polar-ring galaxies. Their unusual disk-ring structure is not yet understood fully. A possibility is that polar rings are the remnants of colossal collisions between two galaxies sometime in the distant past, probably at least 1 billion years ago. What is left of one galaxy has become the rotating inner disk of old red stars in the center. Meanwhile, another smaller galaxy which ventured too close was probably severely damaged or destroyed. During the collision the gas from the smaller galaxy would have been stripped off and captured by the larger galaxy, forming a new ring of dust, gas, and stars, which orbit around the inner galaxy almost at right angles to the old disk. This image of NGC 4560A was created using 3 different color filters (which transmit blue, green, and near-infrared light).
This HST image confirms that the bright central concentration of light, which appears to be slightly orange in this image, has a completely smooth, regular appearance, indicating that it is a dense system composed of older stars and containing little gas or dust. This was once a typical medium-sized galaxy that has been altered, probably by the process that made the complex polar ring. The central dark lanes are due to blockage of light by clouds of gas and dust in the ring, located between us and the inner galaxy. These are the sites of star formation in most galaxies, and NGC 4605A is no exception. The bright bluish clumps, which are especially prominent in the outer parts of the ring, are regions containing luminous young stars, examples of stellar rebirth from the remnants of an ancient galactic disaster. The polar ring appears to be highly distorted. No regular spiral pattern stands out in the main part of the ring, and the presence of young stars below the main ring on one side and above on the other shows that the ring is warped and does not lie in one plane.
Image Title: Ring Around a Galaxy
based on press release for PHOTO NO.: STScI-PRC99-16

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 Last Modified On: Monday, December 18, 2000