Galaxy Silhouettes

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NASA's Hubble Space Telescope has captured a rare alignment between two spiral galaxies. The outer rim of a small, foreground galaxy is silhouetted in front of a larger background galaxy. Skeletal tentacles of dust can be seen extending beyond the small galaxy's disk of starlight.

Such outer dark dusty structures, which appear to be devoid of stars, like barren branches, are rarely so visible in a galaxy because there is usually nothing behind them to illuminate them. Astronomers have never seen dust this far beyond the visible edge of a galaxy. They do not know if these dusty structures are common features in galaxies.

Understanding a galaxy's color and how dust affects and dims that color are crucial to measuring a galaxy's true brightness. By knowing the true brightness, astronomers can calculate the galaxy's distance from Earth.

Astronomers calculated that the background galaxy is 780 million light-years away. They have not as yet calculated the distance between the two galaxies, although they think the two are relatively close, but not close enough to interact. The background galaxy is about the size of the Milky Way Galaxy and is about 10 times larger than the foreground galaxy.

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