NASA's Spitzer Space Telescope has observed a rare population of colliding galaxies whose entangled hearts are wrapped in tiny crystals resembling crushed glass.
The crystals are essentially sand, or silicate, grains that were formed like
glass, probably in the stellar equivalent of furnaces. They are too small and distant to be seen directly, but Spitzer was able
their presence using an instrument, called a spectrograph, that splits light open in the same way that a
prism turns sunlight into a rainbow. This is the first time that silicate crystals have been spotted in a galaxy outside of our own.
"We were surprised to find such delicate, little crystals in the centers of some of the most violent places
in the universe,” said Dr. Henrik Spoon of Cornell University, Ithaca, N.Y. He is first author of a paper on the research appearing in the Feb. 20 issue of 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.”
The discovery will ultimately help astronomers better understand the evolution of galaxies, including our Milky Way, which will merge with the nearby Andromeda galaxy billions of years from now.
“It’s as though there’s a huge dust storm taking place at the center of merging galaxies,” said Dr. Lee Armus, a co-author of the paper from NASA’s Spitzer Science Center at the California Institute of Technology in Pasadena. “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 our sun. On Earth, they sparkle in
sandy beaches, and at night, they can be seen smashing into our atmosphere with other dust particles
as shooting stars. Recently, the crystals were also observed by Spitzer inside comet Tempel 1, which
was hit by NASA’s Deep Impact probe.
The crystal-coated galaxies observed by Spitzer are quite different from our Milky Way. These bright and
dusty galaxies, called ultraluminous infrared galaxies, or “Ulirgs,” are swimming in silicate crystals. While
a small fraction of the Ulirgs cannot be seen clearly enough to characterize, most consist of two spiral-
shaped galaxies in the process of merging into one. Their jumbled cores are hectic places, often bursting
with massive, newborn stars. Some Ulirgs are domnated by central supermassive black holes.
So, where are all the crystals coming from? Astronomers believe the massive stars at the galaxies’ centers are the main manufacturers. According to Spoon and his team, these stars probably shed the crystals both before and as they blow apart in fiery explosions called supernovae.