Cooking Up Life in the Cosmic Kitchen

Ever burnt meat or grilled chicken till the skin was crisp? In the process, the meats released PAHs, complex molecules composed of carbon (shown here at "C") and hydrogen ("H"). This ball-and-stick figure represents benzo[a]pyrene, a PAH commonly produced when cooking food or burning wood has 20 carbon atoms and a dozen hydrogens. Credit: Dennis Bogdan with additions by the author
Ever burnt meat or grilled chicken till the skin was crisp? If you have, you’ve made some PAHs. Overcooked meats, burning wood and automobile exhaust release PAHs, complex molecules composed of carbon (shown here at “C”) and hydrogen (“H”). This ball-and-stick figure represents benzo[a]pyrene, a PAH commonly produced when cooking food or burning wood has 20 carbon atoms and a dozen hydrogens. Credit: Dennis Bogdan with additions by the author
Kitchens are where we create. From crumb cake to corn on the cob, it happens here. If you’re like me, you’ve occasionally left a turkey too long in the oven or charred the grilled chicken. When meat gets burned, among the smells informing your nose of the bad news are flat molecules consisting of carbon atoms arranged in a honeycomb pattern called PAHs or polycyclic aromatic hydrocarbons.

PAHs make up about 10% of the carbon in the universe and are not only found in your kitchen but also in outer space, where they were discovered in 1998. Even comets and meteorites contain PAHs. From the illustration, you can see they’re made up of several to many interconnected rings of carbon atoms arranged in different ways to make different compounds. The more rings, the more complex the molecule, but the underlying pattern is the same for all.

Both simple and complex organic (carbon-containing) molecules have been found in space. Carbon is formed in the cores of red giant stars, where it gets cycled to the surface and dispensed into space. Credit: IAC; original image of the Helix Nebula (NASA, NOAO, ESA, the Hubble Helix Nebula Team, M. Meixner, STScI, & T.A. Rector, NRAO
Both simple and complex organic (carbon-containing) molecules have been found in space. Carbon is formed in the cores of red giant stars, where it gets cycled to the surface and dispensed into space. Credit: IAC; original image of the Helix Nebula (NASA, NOAO, ESA, the Hubble Helix Nebula Team, M. Meixner, STScI, & T.A. Rector, NRAO

All life on Earth is based on carbon. A quick look at the human body reveals that 18.5% of it is made of that element alone. Why is carbon so crucial? Because it’s able to bond to itself and a host of other atoms in a variety of ways to create a lots of complex molecules that allow living organisms to perform many functions. Carbon-rich PAHs may even have been involved in the evolution of life since they come in many forms with potentially many functions. One of those may have been to encourage the formation of RNA (partner to the “life molecule” DNA).

In the continuing quest to learn how simple carbon molecules evolve into more complex ones and what role those compounds might play in the origin of life, an international team of researchers have focused NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) and other observatories on PAHs found within the colorful Iris Nebula in the northern constellation Cepheus the King.

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
This photo is a combination of three infrared color images of the Iris Nebula (NGC 7023) from SOFIA (red & green) and Spitzer (blue) that shows different types of PAH molecules in different parts of the nebula. Credits: NASA/DLR/SOFIA/B. Croiset, Leiden Observatory, and O. Berné, CNRS; NASA/JPL-Caltech/Spitzer

Bavo Croiset of Leiden University in the Netherlands and team determined that when PAHs in the nebula are hit by ultraviolet radiation from its 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.

Strong UV light from a newborn massive star like the one that sets the Iris Nebula aglow would tend to break down large organic molecules into smaller ones, rather than build them up, according to the current view. To test this idea, researchers wanted to estimate the size of the molecules at various locations relative to the central star.

The research team used a telescope on board NASA's SOFIA Observatory, a modified Boeing 747, to fly high above most of the water vapor in the atmosphere to get a better view of PAHs in the Iris Nebula. Credit: NASA
The research team used a telescope on board NASA’s SOFIA Observatory, a modified Boeing 747, to fly high above most of the water vapor in the atmosphere to get a better view of PAHs in the Iris Nebula in infrared light. Credit: NASA

Croiset’s team used SOFIA to get above most of the water vapor in the atmosphere so he could observe the nebula in infrared light, a form of light invisible to our eyes that we detect as heat. SOFIA’s instruments are sensitive to two infrared 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 young star is larger than on the surface of the cloud at the outer edge of the cavity. They also got a surprise: radiation from the star resulted in net growth in the number of complex PAHs rather than their destruction into smaller pieces.

A view of the Iris Nebula in normal or visible light showing the bright, young central star. Light from the star illuminates clouds of gas and dust that show the nebula's flower-like shape. Credit: Hunter Wilson
A view of the Iris Nebula in normal or visible light showing the bright, young central star. Light from the star illuminates clouds of gas and dust that show the nebula’s flower-like shape. Credit: Hunter Wilson

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.

So much starts with stars. Not only do they create the carbon atoms at the foundation of biology, but it would appear they shepherd them into more complex forms, too. Truly, we can thank our lucky stars!

Beautiful Cosmic Barbeque Pit

A new infrared image from NASA's Wide-field Infrared Survey Explorer, or WISE, shows a cosmic barbeque pit, full of PAHS. Image credit: NASA/JPL-Caltech/UCLA

NASA’s Wide-field Infrared Survey Explorer, or WISE has been a busy spacecraft since its launch on Dec. 14, 2009. It has found asteroids and comets, and now has found a cosmic barbeque pit. Well, not really, but the green material in the cloud of gas and dust surrounding the Berkeley 59 cluster is from heated polycyclic aromatic hydrocarbons, (PAHs) molecules that can be found on Earth in barbecue pits, exhaust pipes and other places where combustion has occurred. The “coals,” or the glowing red is warm dust heated by hot young stars within the nebula.
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