[Spitzer-news] NASA's Spitzer Finds Violent Galaxies Smothered in 'Crushed Glass'

spitzer-news at lists.ipac.caltech.edu spitzer-news at lists.ipac.caltech.edu
Wed Feb 15 10:31:58 PST 2006


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

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