ARTICLE

Organic Chemical Reactions in Interstellar Space --"Created  by Quantum Weirdness"

Explanation: Cosmic clouds of gas and dust drift across this magnificent panorama, spanning some 17 degrees near the southern boundary of the heroic constellation Perseus. The collaborative skyscape begins with bluish stars of Perseus at the left, but the eye is drawn to the striking, red NGC 1499. Also known as the California Nebula, its characteristic glow of atomic hydrogen gas is powered by ultraviolet light from luminous blue star Xi Persei immediately to the nebula's right. Farther along, intriguing young star cluster IC 348 and neighboring Flying Ghost Nebula are right of center. Connected by dark and dusty tendrils on the outskirts of a giant molecular cloud, another active star forming region, NGC 1333, lies near the upper right edge of the wide field of view. Shining faintly, dust clouds strewn throughout the scene are hovering hundreds of light-years above the galactic plane and reflect starlight from the Milky Way.

There may be a suite of organic chemical reactions occurring in interstellar space that astronomers haven't considered. In 2012, astronomers discovered methoxy molecules containing carbon, hydrogen and oxygen in the Perseus molecular cloud, around 600 light years from Earth. But researchers were unable to reproduce this molecule in the lab by allowing reactants to condense on dust grains, leaving a mystery as to how it could have formed.

            The answer was found in quantum weirdness that can generate a molecule in space that shouldn't exist by the classic rules of chemistry. In short, interstellar space is a kind of quantum chemistry lab, that may create a host of other organic molecules astronomers have discovered in space. Because of the cold temperatures within the interstellar molecular clouds, reactions with an activation barrier were considered too slow to play an important role for most chemical reactions to occur. The low temperature makes it tough for molecules drifting through space to acquire the energy needed to break their bonds, but some reactions could occur when different molecules stick to the surface of cosmic dust grain. This might give them enough time together to acquire the energy needed to react. "There is a standard law that says as you lower the temperature, the rates of reactions should slow down," says Dwayne Heard of the University of Leeds, UK.

            But methoxy could also be created by combining a hydroxyl radical and methanol gas, both present in space through a process called quantum tunnelling that can give the hydroxyl radical a chance to tunnnel through the energy barrier instead of going over it. Heard and colleagues discovered that despite the presence of a barrier, the rate coefficient for the reaction between the hydroxyl radical (OH) and methanol—one of the most abundant organic molecules in space—is almost two orders of magnitude larger at 63 K than previously measured at ∼200 K. At low temperatures, the molecules slow down, increasing the likelihood of tunnelling. "At normal temperatures they just collide off each other, but when you go down in temperature they hang out together long enough," says Heard.

            The team also observed the formation of the methoxy radical molecule, created by the formation of a hydrogen-bonded complex that is sufficiently long-lived to undergo quantum-mechanical tunnelling. They concluded that this tunnelling mechanism for the oxidation of organic molecules by OH is widespread in low-temperature interstellar environments. The reaction occurred 50 times faster via quantum tunnelling than if it occurred normally at room temperature by hurdling the energy barrier. Empty space is much colder than 63 kelvin, but dust clouds near stars can reach this temperature, added Heard.

"We're showing there is organic chemistry in space of the type of reactions where it was assumed these just wouldn't happen," says Heard.

            The image at the top of the page shows the Perseus Molecular Cloud At microwave wavelengths, taken by the Planck Space Craft which sees electons moving through the Milky Way, and dust being warmed by starlight from stars forming within. These components of the interstellar medium have studied at length over several decades. The electrons are known to emit primarily at radio waves (low frequencies), while the dust grains primarily in the far-infrared (high frequencies).

            In the 1990s, emission was observed which couldn't be explained by either, and became known as "Anomalous Microwave Emission". Several theories of the origin of this emission have been proposed, and now the wavelength coverage of Planck's Low Frequency Instrument is ideal for observing and characterising it.

            An advantage that Planck has is that the combination of the two instruments give a much broader wavelength coverage, which allows the separation of this anomalous emission from the better understood components.

            “We are now becoming rather confident that the emission is due to nano-scale spinning grains of dust, which rotate up to ten thousand million times per second,” says Clive Dickinson from the University of Manchester, who led an analysis of the AME using Planck's maps. “These are the smallest dust grains known, comprising only 10 to 50 atoms; spun up by collisions with atoms or photons, they emit radiation at frequencies between 10 and 60 GHz,” he explains.

            This region in the constellation of Perseus shown was one of two regions within our Galaxy studied in detail. Thanks to Planck's high sensitivity and to its unprecedented spectral coverage, it has been possible to characterise the anomalous emission arising from these two objects in such great detail that many of the alternative theories could be discarded, and to show that at least a significant contribution to the AME, if not the only one, is due to nano-scale spinning dust grains.

            The image at the top of the page shows clouds of gas and dust drifting across the southern boundary of the constellation Perseus. The collaborative skyscape begins with bluish stars of Perseus at the left, but the eye is drawn to the striking, red NGC 1499. Also known as the California Nebula, its characteristic glow of atomic hydrogen gas is powered by ultraviolet light from luminous blue star Xi Persei immediately to the nebula's right. Farther along, intriguing young star cluster IC 348 and neighboring Flying Ghost Nebula are right of center. Connected by dark and dusty tendrils on the outskirts of a giant molecular cloud, another active star forming region, NGC 1333, lies near the upper right edge of the of the wide field of view. Shining faintly, dust clouds strewn throughout the scene are hovering hundreds of light-years above the galactic plane and reflect starlight from the Milky Way. 

Journal reference: Nature Chemistry, DOI: 10.1038/NCHEM.1692

The Daily Galaxy via Nature Chemistry, Space.com, and New Scientist

Image Credit: http://apod.nasa.gov/apod/ap111021.html