Colliding Galaxies in the Visible and InfraredCentaurus A
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Colliding Galaxies in the Visible and Infrared—Centaurus A

August 23, 2005
Centaurus A (NGC 5128) is the nearest active galaxy to Earth. Located 10 million light-years away in the southern constellation Centaurus, “Cen A” appears to be the result of a merger-collision between a large elliptical galaxy (which has a black hole at its center) and a smaller spiral galaxy that veered too close to the larger one, resulting in the cannabalization of the small galaxy.

The visible image (left) from the National Science Foundation's Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory in Chile is dominated by a bright halo of light caused by the stars in the galaxy. Many of these stars are hidden by the dense band of dust that blocks our view of their light.

Infrared light is not so readily obscured by dust as visible light, so the infrared image (right) from the IRAC (at 3.6 and 8 microns) and MIPS (24 microns) instruments on the NASA-JPL Spitzer Space Telescope reveals the complex structure of the dust lane, and the stars and gas embedded within it.

The infrared image is color-coded such that different colors represent different spectral ranges of the observations. Stars, which are bright at 3.6 microns, appear blue. The green indicates organic material in the dust from emissions at 8 microns. Thermal radiation at 24 microns coming from starlight-warmed dust particles is shown in red. When the dust (red) and organics (green) blend together, it appears as yellow in the image. The bright pink dots within the disk are star-forming regions where thermal emission from the warm dust dominates.

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