Image of a nebula taken by NASA’s Spitzer Space Telescope.
Image Credit: NASA/Jet Propulsion Laboratory
Scientists
at NASA's Ames Research Center in Moffett Field, Calif., today released
a significant expansion and upgrade to a public, online database that
houses a unique and extensive collection of information about a family
of complex, carbon-rich molecules that are both widespread and abundant
throughout the universe. Scientists believe more than 20 percent of the
carbon in the universe is tied up in this extensive family of compounds,
collectively know as polycyclic aromatic hydrocarbons, or simply PAHs.
Using the Ames-developed PAH Infrared Spectroscopic Database,
scientists will now have access to data on hundreds more compounds and
several powerful new tools –including an advanced web app and a
dedicated astronomical software package – to map the distribution of
this life-essential element and track its role across the universe.
"Analyzing the PAH emission bands with the web app, new tools, and
expanded database provides a powerful new way for astronomers to trace
the evolution of cosmic carbon and, at the same time, probe conditions
across the universe,” said Christiaan Boersma, a research fellow at Ames
who designed and developed many parts of the web app and tools. "We
have expanded the computational spectral collection to 700 spectra,
including those of extremely large PAHs composed of hundreds of carbon
atoms, and the experimental collection to 75 spectra."
Over the past 20 years, NASA scientists experimentally measured and
computed PAH spectroscopic signatures to track and analyze the
unexpected, widespread PAH emission originating from deep space. NASA
made the original collection of spectra and accompanying software
available online four years ago.
The approach of analyzing the infrared spectra emitted by everything
from dying stars to clouds of gas and dust to entire galaxies using the
one-two punch of known PAH spectra and the new, blind, algorithm-driven
codes now available, provides a unique look into the evolution of cosmic
PAHs.
In addition to substantially increasing the number of spectra
available, the new version of the database includes powerful,
astronomer-friendly tools that mimic the PAHs’ response to the local
space environment and makes it possible to understand which types of
PAHs are present in different regions of space. It also allows
astronomers to tie these evolutionary changes to variations in local
conditions such as those due to the radiation field, physical shape and
history of the region.
"PAHs are so widespread and abundant in space that they don't just
witness the conditions in their cosmic neighborhoods, they are active
participants in many astronomical phenomena," said Louis Allamandola, an
astrophysics researcher at Ames. "PAHs both are an important source of
carbon for young, primordial planets, and influence how quickly they can
form. For example, very bright PAH emission comes from places where new
stars and exo-planets are forming."
NASA's Spitzer Space Telescope managed and operated by NASA's Jet
Propulsion Laboratory in Pasadena, Calif., detected the PAH signature
across the universe and showed PAHs were already forming only a couple
of billion years after the Big Bang. Because their spectral signature is
very sensitive to their local environment, especially radiation levels,
the temperatures of PAHs in space can vary from nearly minus 450
degrees Fahrenheit to roughly 1,000 degrees, after which they break
apart.
“Since PAHs are so sensitive to local conditions, analyzing the PAH
bands as we did here represents a powerful new astronomical tool to
trace the evolution of cosmic carbon and, at the same time, probe
conditions in objects spanning the universe,” said Allamandola.
The upgraded database allows scientists to determine how the PAH
signature changes across this vast range of temperatures. Astronomers
need simply to upload the spectra of their favorite celestial object
into the website and see which PAH classes are needed to reproduce their
spectra.
"This capability is a major step forward because it allows
astronomers to directly tie their astronomical spectra to the spectra of
individual, bona-fide PAHs, not generic, model dependent, mythical,
cosmic material," said Allamandola. "And they can do all this on their
mobile devices like iPads and iPhones, as well as personal computers."
PAHs in space are probably made the same way soot is made in the
combustion engines that power trucks and cars here on Earth. In addition
to astronomical applications, the expanded PAH database and powerful
new software also is a useful research tool for scientists, educators,
policy makers, and consultants working in the fields of medicine,
health, chemistry, fuel composition, engine design, environmental
assessment, environmental monitoring and protection, and nanotechnology.
This work was supported by NASA's Astrobiology and Laboratory
Astrophysics Programs and Carbon in the Galaxy Consortium under the
auspices of the Astrophysics Research and Analysis Program.
Rachel Hoover
NASA's Ames Research Center, Moffett Field, Calif.
