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.
Most of the stars speckled across this image
belong to the nearby spiral galaxy NGC 253, which is out of view to the right.
Astronomers used Hubble's Advanced Camera for Surveys to snap images of NGC 253
when they spied the two galaxies in the background. From ground-based
telescopes, the two galaxies look like a single blob. But the Advanced Camera's
sharp "eye" distinguished the blob as two galaxies, cataloged as
2MASX J00482185-2507365. The images were taken on Sept.
19, 2006 .
The results have been submitted for publication
in The Astronomical Journal.
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