Combination of three color images of NGC 7023 from
SOFIA (red & green) and Spitzer (blue) show different populations of
PAH molecules. Credits: NASA/DLR/SOFIA/B. Croiset, Leiden Observatory, and O. Berné, CNRS; NASA/JPL-Caltech/Spitzer.
Using data collected by NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA)
and other observatories, an international team of researchers has
studied how a particular type of organic molecules, the raw materials
for life – could develop in space. This information could help
scientists better understand how life could have developed on Earth.
Bavo Croiset of Leiden University in the Netherlands and his
collaborators focused on a type of molecule called polycyclic aromatic
hydrocarbons (PAHs), which are flat molecules consisting of carbon atoms
arranged in a honeycomb pattern, surrounded by hydrogen. PAHs make up
about 10 percent of the carbon in the universe, and are found on the
Earth where they are released upon the burning of organic material such
as meat, sugarcane, wood etc. Croiset’s team determined that when PAHs
in the nebula NGC 7023, also known as the Iris Nebula, are hit by
ultraviolet radiation from the nebula’s central star, they evolve into
larger, more complex molecules. Scientists hypothesize that the growth
of complex organic molecules like PAHs is one of the steps leading to
the emergence of life.
Some existing models predicted that the radiation from a newborn,
nearby massive star would tend to break down large organic molecules
into smaller ones, rather than build them up. To test these models,
researchers wanted to estimate the size of the molecules at various
locations relative to the central star.
Croiset’s team used SOFIA to observe Nebula NGC 7023 with two
instruments, the FLITECAM near-infrared camera and the FORCAST
mid-infrared camera. SOFIA’s instruments are sensitive to two
wavelengths that are produced by these particular molecules, which can
be used to estimate their size. The team analyzed the SOFIA images in
combination with data previously obtained by the Spitzer infrared space
observatory, the Hubble Space Telescope and the Canada-France-Hawaii
Telescope on the Big Island of Hawaii.
The analysis indicates that the size of the PAH molecules in this
nebula vary by location in a clear pattern. The average size of the
molecules in the nebula’s central cavity, surrounding the illuminating
star, is larger than on the surface of the cloud at the outer edge of
the cavity.
In a paper published in Astronomy and Astrophysics,
The team concluded that this molecular size variation is due both to
some of the smallest molecules being destroyed by the harsh ultraviolet
radiation field of the star, and to medium-sized molecules being
irradiated so they combine into larger molecules. Researchers were
surprised to find that the radiation resulted in net growth, rather than
destruction.
“The success of these observations depended on both SOFIA’s ability
to observe wavelengths inaccessible from the ground, and the large size
of its telescope, which provided a more detailed map than would have
been possible with smaller telescopes,” said Olivier Berné at CNRS, the
National Center for Scientific Research in Toulouse, France, one of the
published paper’s co-authors.
For more information SOFIA Science, go to: https://www.sofia.usra.edu/
Dr. Dana Backman
SOFIA Science Center, NASA Ames Research Center, Moffett Field, California
Kassandra Bell
SOFIA Science Center, NASA Ames Research Center, Moffett Field, California
Editor: Kassandra Bell
Source: NASA/SOFIA
