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The brightest object in this picture is NGC 4881, approximately centered here in the Planetary Camera (the small quadrant). It is a 13th-magnitude elliptical galaxy in the outskirts of the Coma Cluster, a great cluster of galaxies more than 5 times farther away than the Virgo Cluster. Except for a 16th-magnitude Coma spiral at the right and a few foreground stars of the Milky Way, nearly everything else in this field lies far beyond the Coma Cluster. There is a fascinating assortment of background galaxies, including an apparent galaxian merger in progress.
Purpose: This HST-WFPC2 observation was made to explore the use the globular star clusters surrounding NGC 4881 as distance indicators for inferring the distance to the Coma Cluster. They are barely visible point sources in this reproduction. The distance to the Coma Cluster is an important cosmic yardstick for scaling the over all size of the universe, because Coma (unlike Virgo) is far enough away that regional departures from a smooth expansion of the universe should not be a major source of uncertainty if Coma is used for estimating the age and rate of expansion (the Hubble Constant).
Credits: Hubble Space Telescope WFPC Team, Caltech; NASA
Courtesy: Space Telescope Science Institute (STScI)
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