It Turns Out That The Milky Way Is Really Quite Greasy

An illustration of the structure of an aliphatic hydrocarbon. Credit: D. Young (2011), The Galactic Center. Flickr – CreativeCommons

A new analysis from an Australian-Turkish team of researchers suggests that our own galaxy is rich in grease-like molecules. These carbon-based molecules are one of the components of interstellar dust but it wasn’t exactly clear just how abundant they were compared to other components.

The researchers went about recreating this dust in the lab, starting from similar components and conditions to obtain materials with the same properties. They then estimated the abundance of aliphatic hydrocarbon molecules (the technical name for the grease). The team estimates that there are 10 billion trillion trillion tonnes of greasy matter in the Milky Way, equivalent to a mass of 5 million Suns. These findings are published in the Monthly Notices of the Royal Astronomical Society.

"Combining our lab results with observations from astronomical observatories allows us to measure the amount of aliphatic carbon between us and the stars," co-author Professor Tim Schmidt, from the University of New South Wales, said in a statement. "This space grease is... dirty, likely toxic and only forms in the environment of interstellar space (and our laboratory). It's also intriguing that organic material of this kind – material that gets incorporated into planetary systems – is so abundant."

The scientists came up with an ingenious way to mimic the processes that create these molecules. It is believed that aliphatic hydrocarbons form in the outflow of older stars that have become enriched with carbon. The team expanded a carbon-containing plasma in a vacuum at low temperature and new molecules formed.

The molecules were collected and studied. The researchers determined how effective the greasy substance was at absorbing certain infrared light. They compared the results with astronomical observations and estimated that there are about 100 carbon atoms for every 1 million hydrogen atoms that make interstellar dust.

Astronomers believe that roughly half of all the carbon in the galaxy is trapped inside stars, while the rest is distributed in interstellar dust and a (relative) sprinkle can be found in planets and smaller objects. Understanding where the carbon molecules are and how abundant they are can help us better understand planetary formation. The next step for the researchers will be to estimate the prevalence of the other common type of hydrocarbon, the aromatic one. Naphthalene, a key component of mothballs, is an aromatic hydrocarbon. Being greasy and smelling of mothballs might not be a great look for our galaxy. 

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