The crystals - essentially sand, or silicate, grains that were formed like glass, probably in stellar furnaces - are the first detected outside of the Milky Way.

"We were surprised to find such delicate little crystals in the centers of some of the most violent places in the universe," said Henrik Spoon of Cornell University, lead author of the paper appearing in the Feb. 20 issue of the Astrophysical Journal. "Crystals like these are easily destroyed, but in this case, they are probably being churned out by massive, dying stars faster than they are disappearing."

Spoon said the discovery should help astronomers improve their understanding of the evolution of galaxies, including the Milky Way, which billions of years from now will collide with the nearby Andromeda.

"It's as though there's a huge dust storm taking place at the center of merging galaxies," said co-author Lee Armus, with NASA's Spitzer Science Center. "The silicates get kicked up and wrap the galaxies' nuclei in giant, dusty glass blankets."

Silicates, like glass, require heat to transform into crystals. The gem-like particles can be found in the Milky Way in limited quantities around certain types of stars, such as the Sun. On Earth, they sparkle on sandy beaches and, at night, they can be seen smashing into the atmosphere with other dust particles as shooting stars. Recently, the Spitzer also observed the crystals inside comet Tempel 1, which was hit by the Deep Impact probe last July 4.

The crystal-coated galaxies observed by Spitzer are quite different from the Milky Way, however. The distant bodies are called ultraluminous infrared galaxies, or "Ulirgs," and they are swimming in silicate crystals. A small fraction of the Ulirgs cannot be seen clearly enough to characterize, but most consist of two spiral-shaped galaxies in the process of merging into one. Their jumbled cores are hectic and extremely violent places, often bursting with massive newborn stars, and some dominated by central supermassive black holes.

Astronomers hypothesize that massive stars at the galaxies' centers are the crystals' main manufacturers. Spoon and colleagues write that the stars probably shed the crystals both before and as they blow apart in supernovae, but the delicate crystal materials don't last long. They think particles from supernova blasts bombard and convert the crystals back to a shapeless form, in a process thought to be relatively short-lived.

"Imagine two flour trucks crashing into each other and kicking up a temporary white cloud," Spoon said. "With Spitzer, we're seeing a temporary cloud of crystallized silicates created when two galaxies smashed together."

Spitzer's infrared spectrograph spotted the silicate crystals in 21 of 77 Ulirgs it has studied. The 21 galaxies range from 240 million light-years to 5.9 billion light-years away and are scattered across the sky.

Spoon said Spitzer most likely caught the galaxies at just the right time to see the crystals, which is why the other 56 seem to lack them. Those galaxies might be about to kick up the crystals, or they could have already vanished, he added.

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