Anne’s Picture of the Day: Overlapping Galaxies NGC 3314

April 4, 2013

NGC 3314, a pair of overlapping galaxies in Hydra

NGC 3314A & NGC 3314B

Image Credit: Hubble Legacy Archive, ESA, NASA; Processing: Martin Pugh (

NGC 3314 is actually a pair of overlapping galaxies that lie 117 million (NGC 3314A) and 140 million (NGC 3314B) light-years away in the southern constellation of Hydra. They are separated by tens of millions of light-years of void and are physically unrelated. NGC 3314A is receding from us at approximately 2851 kilometers per second while the background galaxy is moving away from Earth at about 4641 kilometers per second.

Through an extraordinary chance alignment, the face-on barred spiral galaxy (NGC 3314A) of some 55 thousand light-years across, lies precisely in front the other, larger lenticular galaxy (NGC 3314B), which spans nearly 70,000 light-years at its estimated distance.

The outer spiral arms of NGC 3314A appear to change from bright to dark, as they are projected first against deep space, and then against the bright background of the other galaxy. Its pinwheel shape is dominated by swirling dark dust lanes, but we can also see several bright star clusters. The bright blue stars in these clusters have formed only recently from interstellar gas and dust.

NGC 3314A’s warped shape is likely due to an encounter with another galaxy, perhaps nearby NGC 3312 (visible to the north in wide-field images) or another nearby galaxy, but definitely not NGC 3314B, since we know they are not and have never been physically related.

NGC 3314B’s dust lanes appear far lighter than those of NGC 3314A. This is not because that galaxy lacks dust, but rather because they are lightened by the bright fog of stars in the foreground. NGC 3314A’s dust, in contrast, is backlit by the stars of NGC 3314B, silhouetting them against the bright background.

A small, red-orange patch near the center of the image is the bright nucleus of NGC 3314B. It is reddened for the same reason the setting sun looks red. When light passes through a volume containing small particles (molecules in the Earth’s atmosphere or interstellar dust particles in galaxies), its color becomes redder.

This unique alignment provides us with the rare chance to visualize dark material within NGC 3314a, seen only because it is silhouetted against the object behind it. Dust lying in the spiral arms of the foreground galaxy stands out where it absorbs light from the more distant galaxy. This silhouetting shows us where the interstellar dust clouds are located, and how much light they absorb.

A synthetic third channel was created to construct this dramatic composite of the overlapping galaxies from two color image data in the Hubble Legacy Archive.

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