Hubble spies a cluster's unruly past.

Streams of stars torn from galaxies. Pairs of galaxies sculpted into odd shapes. These images of a distant galaxy cluster suggest that the good old days were plenty violent.

The Hubble Space Telescope found that 13 of 81 galaxies in the remote cluster MS 1054-03 are either remnants of collisions or were caught in the act of colliding. Most of the 13 are massive. For a single cluster, that's the largest number of galaxies ever found to show evidence of collision, report Dutch astronomer Pieter G. van Dokkum of the Kapteyn Astronomical Institute in Groningen and the Leiden Observatory and his colleagues in the Aug. 1 ASTROPHYSICAL JOURNAL LETTERS.

The Hubble images, recording light that left the galaxies 8 billion years ago, reveal what the cluster looked like in its youth. More mature clusters show fewer collisions. The new observations confirm the prevailing view that massive galaxies form through collisions of smaller ones over an extended period, An earlier theory suggested that these behemoths emerged in one big baby boom.

During collisions, galaxies typically don't plow into each other but pass so close that their mutual gravity distorts the orbits of their stars. Astronomers have suggested that when two spiral galaxies merge, they form a blobby elliptical galaxy. Van Dokkum's team argues that the new observations support that scenario. Harry C. Ferguson of the Space Telescope Science Institute in Baltimore cautions that MS 1054-03 may not be a typical cluster.