Mysteries Between Stars

We know that solar systems form in a disk shape, with the star forming in the middle and any other rocks, presumably planets, form out from the center in whatever dust and gas remains. But what about the space between stars? Is it truly empty? And if there is something out there, how could we find it? How did it get there?

This artist’s conception symbolically represents complex organic molecules, known as polycyclic aromatic hydrocarbons, seen in the early universe. These large molecules, comprised of carbon and hydrogen, are among the building blocks of life. Credit: NASA/JPL-Caltech/T. Pyle (SSC)

For years, astronomers and chemists (believe it or not) have been trying to answer these questions and more.  The specific problem is that when we take a spectrum of a distant star, we see a collection of 400 or so absorption features that have been named the Diffuse Interstellar Bands (DIB).  After decades of research, the identity of the DIBs remain elusive, though research seems to indicate that they are formed by a collection of hydrocarbon molecules that have not been reproduced in a laboratory on Earth, and hence do not have a recorded spectrum.

Diffuse Interstellar Bands shown across the visible spectrum.

Of all the potential candidate molecules, Polycyclic Aromatic Hydrocarbons (PAH) are considered the most promising, since they have been observed in the interstellar medium previously.  However, the width of the DIB features, which indicate the lifetimes of excited states in the absorption process, are considered an argument against PAHs.

However, astronomers from university of Lyon aided by theoretical input from scientists at the universities of Heidelberg, Hyderabad and Leiden, have performed an experiment showing that the lifetimes of excited states for small and medium sized PAHs are consistent with the DIB line widths.

People often ask me how often I get to look at telescopes as an astronomer, and the answer is not very much.  Astronomy is a science that is influenced by technology and a wide range of other sciences performed in laboratories all around the world.  Chemistry, Biology, Geology, and Climatology are just some of the sciences that help us uncover the mysteries of the universe, both large and small scale.

Future laboratory work will help us pinpoint the culprit when it comes to the DIBs, giving us an understanding of what is actually happening in the vast space between stars.

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