Electrically charged ‘soccer balls’ spotted by Hubble solving an interstellar mystery

Using the Hubble Space Telescope, scientists have been able to verify the presence of electrically charged molecules — C60+ or ‘Bucky Balls’ — in interstellar space.

This is an artist’s concept depicting the presence of buckyballs in space. Buckyballs, which consist of 60 carbon atoms arranged like soccer balls, have been detected in space before by scientists using NASA’s Spitzer Space Telescope. The new result is the first time an electrically charged (ionized) version has been found in the interstellar medium.

The discovery of electrically-charged molecules in space shaped like soccer balls, finally sheds light on the constituents of the interstellar medium (ISM) — the gas and dust that fills interstellar space.

As planets and stars form from ISM when perturbances cause it to collapse, investigations about its composition tell us a great deal about the formation of stars, planets and even, life itself.

Martin Cordiner of the Catholic University of America, Washington, explains further: “The diffuse ISM can be considered as the starting point for the chemical processes that ultimately give rise to planets and life.

“So fully identifying its contents provides information on the ingredients available to create stars and planets.”

Cordiner — who is stationed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland — and his team identified these molecules as a form of carbon called “Buckminsterfullerene” — or “Buckyballs” — which consists of 60 carbon atoms (C60) arranged in a hollow sphere. C60 has been found in some rare cases on Earth in rocks and minerals, and can also turn up in high-temperature combustion soot.

Whilst C60 has been seen in space before, this is the first time an electrically charged — ionised — version has been confirmed to be present in the diffuse ISM.

A schematic of a C60 molecule — referred to as ‘Bucky Balls’ detected in ISM for the first time by this research

The fact that the C60 is in an ionised state is telling. C60 is ionised when ultraviolet light from stars tears off an electron from the molecule, resulting in it having a positive charge. The resulting ionised molecule is called C60+.

Cordiner, the lead author of a paper on this research published in the Astrophysical Journal Letters, explains: “The diffuse ISM was historically considered too harsh and tenuous an environment for appreciable abundances of large molecules to occur.

“Prior to the detection of C60, the largest known molecules in space were only 12 atoms in size. Our confirmation of C60+ shows just how complex astrochemistry can get, even in the lowest density, most strongly ultraviolet-irradiated environments in the Galaxy.”

Life as we know it is based on carbon-bearing molecules, thus this discovery showing that complex carbon molecules can form and survive in the harsh environment of interstellar space is significant to both investigations of how life began here on Earth and where else in the universe it is likely to be found.

Cordiner continues: “In some ways, life can be thought of as the ultimate in chemical complexity.

“The presence of C60 unequivocally demonstrates a high level of chemical complexity intrinsic to space environments, and points toward a strong likelihood for other extremely complex, carbon-bearing molecules arising spontaneously in space.”

Whilst hydrogen and helium comprises the vast majority of the ISM, many other compounds — yet to be identified — run throughout it. To study the composition of this remote gas and dust, scientists observe how it affects the light from distant stars.

Spectroscopy — fingerprinting starlight

As the light from distant stars passes through space, elements and compounds in the ISM absorb certain wavelengths of the light and emit light in others. Spectroscopy is a method that splits this starlight it into its component wavelengths — with those that have been absorbed appearing dim, or absent.

The key to this identification method is the fact that every element or compound has a unique absorption pattern allowing it to be identified.

The spectroscopic ‘fingerprints’ of different chemical elements allows for their identification in the ISM

Some absorption patterns from the ISM cover a broader range of colours, which appear different from any known atom or molecule on Earth. These absorption patterns are called Diffuse Interstellar Bands — DIBs. Their identity has remained a mystery ever since they were discovered by Mary Lea Heger, who published observations of the first two DIBs in 1922.

A DIB can be assigned by finding a precise match with the absorption fingerprint of a substance in the laboratory. However, there are millions of different molecular structures to try, so it would take many lifetimes to test them all.

Cordiner explains the challenge further: “Today, more than 400 DIBs are known, but — apart from the few newly attributed to C60+ — none have been conclusively identified.

“Together, the appearance of the DIBs indicate the presence of a large amount of carbon-rich molecules in space, some of which may eventually participate in the chemistry that gives rise to life. However, the composition and characteristics of this material will remain unknown until the remaining DIBs are assigned.”

Until now, decades of laboratory studies have failed to find a precise match with any DIBs until the work on C60+.

The spectral pattern of C60+ ( P Jenniskens, F -X Desert)

Cordiner and his team were able to match the absorption pattern seen from C60+ in the laboratory to that from collected from Hubble observations of the ISM — in part, building upon work conducted by a team from the University of Basel, Switzerland, which provided the required C60+ comparison data.

Why the Hubble Space Telescope?

The major hindrance in detecting C60+ using conventional, ground-based telescopes comes from atmospheric water vapour which obscures the view of the C60+ absorption pattern.

The Hubble Space Telescope’s position high above Earth’s atmosphere means it is uniquely positioned to identify the faint ‘fingerprints’ of C60+ (NASA)

From its position high above Earth’s atmosphere, the Hubble telescope doesn’t suffer from this blocking — known as ‘extinction’ — an thus, has a clear, unobstructed view. Even with this the case, the team still had to push Hubble far beyond its usual sensitivity limits for it to stand a chance of detecting the faint fingerprints of C60+.

The observed stars were all blue supergiants, located in the plane of our Galaxy — the Milky Way. Because the Milky Way’s interstellar material is primarily located in a relatively flat disk — lines of sight to stars in the Galactic plane traverse the huge quantities of interstellar matter. This means they show the strongest absorption features due to interstellar molecules.

Matching expectations and future investigations

Thus far the detection of C60+ in the diffuse ISM supports the team’s expectations that very large, carbon-bearing molecules are likely candidates to explain many of the remaining, unidentified DIBs.

This suggests that future laboratory efforts should measure the absorption patterns of compounds related to C60+to help identify some of the remaining DIBs.

The team is seeking to detect C60+ in more environments to see just how widespread buckyballs are in the Universe. According to Cordiner, based on their observations so far, it seems that C60+ is very widespread in the Galaxy.

Original research: https://iopscience.iop.org/article/10.3847/2041-8213/ab14e5