Cosmic Crashes

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Science  07 Oct 2005:
Vol. 310, Issue 5745, pp. 19
DOI: 10.1126/science.310.5745.19d

Like cheese stirred into hot soup, the gravitational mixing of giant clusters of galaxies leaves behind faint tidal trails of stars and streamers of gas. These fossils give astronomers clues as to the past dynamical history of the cluster, including collisions and interactions between its members, but the streaks can be difficult to see because they are very faint and distorted by instrumental effects in telescope images.

Mihos et al. have imaged the weak diffuse glow from intra-cluster light in the well-known and nearby Virgo cluster. At a distance of only 16 million parsecs, Virgo covers an area of several degrees on the sky, so obtaining deep and uniform images over such a wide area has been tricky. These images show a web of tidal tails and bridges between galaxies, as well as common envelopes of gas and stars circling galaxy groups. The clumpiness of the diffuse light shows that the cluster formed from many smaller galaxy groups crashing together—the process of hierarchical assembly—rather than growing smoothly from steady accretion. — JB

Astrophys. J. 631, L41 (2005).

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