Insight
Diffuse Interstellar Bands:inThe Diamonds the Graveyard of Many a Career Rough By Larissa Aravantinou By Tom Neal
S
pace is filled with stars and planets. Between these celestial bodies are gaps filled with thinly spread gas and dust known as interstellar dust clouds. Through telescopes scientists can take a look into space and use measurements of electromagnetic radiation to determine which particles are present in the interstellar medium. This is possible because atoms and molecules interact with radiation in different ways. Consequently, different atoms and molecules have characteristic patterns of absorption. Scientists can then use this information to match absorption patterns of known atoms or molecules with the patterns observed in space.1 But what if the absorption patterns in space don’t match to those of any atom or molecule known to scientists? That is exactly the case with the Diffuse Interstellar Bands (DIBs). The Diffuse Interstellar Bands are absorption bands belonging to interstellar material in space known as carriers. There are over 500 DIBs that range between 4000 Å to 10000 Å as shown above. They have baffled scientists for over 100 years since their first discovery by Mary Lea Heger in 1919. This is because despite many DIBs having been detected, there is only one molecule that has been found to match two diffuse interstellar bands at 9577 Å and 9632 Å - and that is the C60+ buckminsterfullerene cation.2 The confirmation of C60+ as a carrier in 2015 signified a breakthrough in the research of diffuse interstellar bands and the understanding of the interstellar medium. It meant that larger, more complex structures may
3 Resonance Issue 14
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Infrared Spectrum detailing the apearance of diffuse interstellar bands.1
exist in interstellar space compared to what was previously thought. There may even be molecules in the interstellar medium that have never been observed on Earth!2 Astronomers assume that some of the DIB carriers may be polyaromatic hydrocarbons or other larger fullerenes. However, btaining laboratory evidence to confirm these carriers is extremely difficult since it requires scientists to essentially replicate the conditions of deep space in a lab. The molecules have to be isolated in temperatures as low as 4.2 K in neon or helium matrices in order to obtain their gas phase spectra and compare them to absorption spectra from space.3 Moreover, whilst there is some clue as to the identity of the DIB carriers, nobody really knows how they actually got there. So far speculations suggest that they are formed in the atmosphere of carbon rich stars and are then carried into space by the star’s stellar wind. However this is far from conclusive.3
There is still a lot to be uncovered in regards to the chemical and physical reactions occurring in the interstellar medium and in space. Whilst astronomers are one step closer to identifying carriers for the DIBs, the fascinating century-old mystery continues.
Female astronomer Mary Lea Heger, who made important discoveries in interstellar medium.
1. https://bit.ly/3dsSfj5 2. https://bit.ly/32qlz3u 3. https://bit.ly/32qlz3u
