Organic matter of different kinds contains carbon, an element considered essential for life. There is though real uncertainty over its abundance, and only half the carbon expected is found between the stars in its pure form. The rest is chemically bound in two main forms: aliphatic and aromatic. A team of astronomers and materials scientists from Australia and Turkey has created laboratory analogues of interstellar dust and used their results to estimate the amount of aliphatic (grease-like) molecules found in our Milky Way Galaxy.
An illustration of the structure of a greasy carbon molecule, set against an image of the Milky Way’s center, where this material has been detected; carbon is represented as gray spheres and hydrogen as white spheres. Image credit: D. Young.
The researchers from the University of New South Wales and Ege University mimicked the process by which organic molecules are synthesized in the outflows of carbon stars, by expanding a carbon-containing plasma into a vacuum at low temperature.
Using magnetic resonance and spectroscopy, they were able to determine how strongly the material absorbed light with a certain infrared wavelength, a marker for aliphatic carbon.
“Combining our lab results with observations from astronomical observatories allows us to measure the amount of aliphatic carbon between us and the stars,” said University of New South Wales’ Professor Tim Schmidt, co-author of the study.
Professor Schmidt and colleagues found that there are about 100 greasy carbon atoms for every million hydrogen atoms, accounting for between a quarter and a half of the available carbon.
“In the Milky Way, this amounts to about 10 billion trillion trillion tons of greasy matter, or enough for 40 trillion trillion trillion packs of butter,” Professor Schmidt said.
“This space grease is not the kind of thing you’d want to spread on a slice of toast. It’s dirty, likely toxic and only forms in the environment of interstellar space (and our laboratory),” he added.
“It’s also intriguing that organic material of this kind — material that gets incorporated into planetary systems — is so abundant.”
The scientists now plan to determine the abundance of aromatic carbon, which will involve yet more challenging work in the lab.
By firmly establishing the amount of each type of carbon in the interstellar dust, they will know precisely how much of this element is available to create life.
The study was published online in the Monthly Notices of the Royal Astronomical Society.
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B. Günay et al. Aliphatic Hydrocarbon Content of Interstellar Dust. MNRAS, published online June 18, 2018; doi: 10.1093/mnras/sty1582
