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.
This is the first time silicate crystals have been detected 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
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."
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 dominated 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. But the delicate crystals won't
be around for long. The scientists say that particles from
supernova blasts will bombard and convert the crystals back to a
shapeless form. This whole process is thought to be relatively
short-lived.
"Imagine two flour trucks crashing into each other and kicking
up a temporary white cloud," said Spoon. "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 studied. The 21 galaxies range from 240 million to
5.9 billion light-years away and are scattered across the sky.
Spoon said the galaxies were most likely caught at just the right
time to see the crystals. The other 56 galaxies might be about to
kick up the substance, or the substance could have already
settled.
Others authors of this work include Drs. A.G.G.M. Tielens and J.
Cami of NASA's Ames Research Center, Moffett Field, Calif.; Drs.
G.C. Sloan and Jim R. Houck of Cornell; B. Sargent of the
University of Rochester, N.Y.; Dr. V. Charmandaris of the
University of Crete, Greece; and Dr. B.T. Soifer of the Spitzer
Science Center.
The Jet Propulsion Laboratory manages the Spitzer Space
Telescope mission for NASA's Science Mission Directorate,
Washington. Science operations are conducted at the Spitzer Science
Center. JPL is a division of Caltech. Spitzer's infrared
spectrograph was built by Cornell University, Ithaca, N.Y. Its
development was led by Dr. Jim Houck.