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Virgo Cluster of Galaxies—Intracluster Light

Over the course of two months in March and April 2004, on clear moonless nights, the Burrell Schmidt telescope took a series of seventy-two 15-minute exposures of the Virgo Cluster.

The images were then combined to make a composite wide-field image, with the exquisite sensitivity needed to detect the very faint intracluster light— light that is nearly 1000 times fainter than the dark night sky itself.

The first image (black and white) shows the normal exposure of the Virgo Cluster.  The second image (black and orange) shows the Virgo Cluster in its true glory, revealing the complex, diffuse web of starlight that fills the space between the galaxies in the cluster. Many long streamers of stars can be seen, along with very faint extended halos surrounding the bright galaxies, and several groups of galaxies embedded in faint "common envelopes" of light.

This diffuse intracluster light, formed from the repeated collisions of galaxies within the cluster, represents an archaeological "history" of the formation and evolution of the Virgo Cluster.

We can use computer simulations to study how intracluster light forms. When two galaxies collide, the gravitational forces between the galaxies rip out long streamers of stars known as "tidal tails." When many galaxies collide inside a galaxy cluster (see movie), these tidal tails get strewn throughout the cluster and form the diffuse intracluster light.