Hostile Beginnings for Components of Life (Forwarded)

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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
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http://www.jpl.nasa.gov

March 2, 2006

Hostile Beginnings for Components of Life
By Linda Vu, Spitzer Science Center

The components of life may have been under attack in the hostile
environments of the universe's first galaxies, say astronomers using
NASA's Spitzer Space Telescope.

A science team led by graduate student Yanling Wu of Cornell University,
Ithaca, N.Y., recently came to this conclusion after studying the
formation and destruction of polycyclic aromatic hydrocarbons molecules
(PAHs) in more than 50 blue compact dwarf (BCD) galaxies. These organic
molecules, comprised of hydrogen and carbon, are believed by many
scientists to be among the building blocks for life.

"One of the outstanding problems in astronomy today is whether complex
organic molecules of hydrogen and carbon, similar to those responsible for
life on Earth, are present in the early universe," says Wu.

According to Wu, mature massive galaxies like our Milky Way formed from
the merging of smaller galaxies, probably about the size of nearby BCD
galaxies. Since current technology is not sensitive enough to easily
identify and study in detail the universe's first galaxies, astronomers
must infer the physical properties of the early structures by observing
similar nearby galaxies like BCDs.

"We believe that BCD galaxies are similar to the universe's first galaxies
because they are infant galaxies, actively forming stars, and are not very
chemically polluted," said Wu.

Because most atomic elements other than hydrogen and helium are born from
the death of stars, astronomers suspect that in the first few million
years after the big bang galaxies were not "chemically polluted" with
elements other than hydrogen and helium. In astronomy, these relatively
unpolluted galaxies are said to have low metallicity.

The BCD galaxies' blue colors tell astronomers that these structures are
actively forming massive stars. By logically combining the galaxy's blue
color with the fact that it is low in metals, astronomers can infer that
this is a young galaxy.

In her research, Wu found that nearby BCD galaxies with lowest metallicity
also had little or no PAHs. As the galaxies became more chemically
polluted, more traces of PAHs were found. She notes that this phenomenon
makes sense because heavy metal elements like carbon are formed from the
death of stars, and some of these galaxies may just be too "young" to have
produced enough carbon to create PAHs.

However, in some of the BCD galaxies where the conditions allow for the
formation of PAHs, Wu found that those molecules were being destroyed by
intense ultraviolet radiation from the young massive stars.

"Because BCD galaxies are metal poor and very compact, the intense
ultraviolet radiation from young stars will destroy PAH molecules even if
they are formed," says Wu. "The threshold for when these PAH molecules
stop being destroyed is still uncertain."

"This leads to an interesting paradox, where the young stars responsible
for the formation of PAHs may also be the main culprit of their
destruction," adds co-author Dr. Vassilis Charmandaris, of the University
of Greece, Heraklion.

The organic PAHs were detected using Spitzer's Infrared Spectrometer
(IRS).

"Yanling has made significant progress in a research area first opened by
International Space Observatory ," says Dr. Jim Houck of Cornell
University. Houck is Wu's academic advisor and a co-author of the paper.
He is also the Principal Investigator for Spitzer's IRS instrument and
played a vital role in its creation.

"With Spitzer, Yanling is able to extend BCDs observations to a much
larger sample; the new results provide a glimpse into the formation of
galaxies in the early Universe," he adds.

Wu's paper will be published in a March issue of Astrophysical Journal.
For more information on this discovery please listen to the podcast
interview with Yanling Wu,

http://www.spitzer.caltech.edu/featu...302Spitzer.mp3

The Spitzer Space Telescope is a NASA mission managed by the Jet
Propulsion Laboratory.

IMAGE CAPTION:
[http://www.spitzer.caltech.edu/Media...60302/pahs.jpg
(140KB)]
This artist's conception symbolically represents complex organic
molecules, known as polycyclic aromatic hydrocarbons, seen in the early
universe.

Credit: NASA/JPL-Caltech/T. Pyle (SSC/Caltech)