The upper limit for molecules swirling around in the diffuse bands of material between stars, known as the interstellar medium (ISM), has moved sharply upward with the confirmation that they contain Buckminsterfullerene.
The molecules, sometimes also known as “buckyballs”, comprise 60 carbon atoms arranged in a shape resembling a soccer ball. Previous research into the contents of the diffuse ISM had detected molecules with no more than three atoms.
Figure 1. Nightly sum spectra of the K i λ7698, Ca ii λ3968, and Na i λ5895 absorption lines toward SN 2014J. There are no significant changes in these absorption features over the 37 days sampled by our observations (see also Figure 2). Only four epochs are shown for Ca ii λ3968 because the supernova had very little blue flux on the remaining nights, making those Ca ii spectra unreliable.
The discovery was made by a team headed by physicist Martin Cordiner of NASA’s Goddard Space Flight Centre, using data obtained by the Hubble Space Telescope.
The hundreds of absorption bands in the ISM are variously visible in spectra ranging from visible light to near infra-red. The bands are not produced by stars, and must thus be the product of light absorption by extremely diffuse matter.
Determining precisely which forms of matter are in the mix has long been an ongoing project for many teams of astronomers – a task complicated by the fact that terrestrial telescopes must first account for the competing absorption features of the Earth’s own atmosphere.
The Hubble Space Telescope, being outside the planet’s atmosphere, neatly solves at least part of the problem.
To solve the rest, Cordiner and colleagues made use of the craft’s Space Telescope Imaging Spectrograph (STIS) to observe 11 target stars, and the spaces between them, generating data with an extremely high signal-to-noise ratio.
The observations were made between November 2016 and August 2018.
Using a technique that took the known absorption features of helium atoms as a standard marker, the researchers were able to confidently confirm the presence of buckyballs in the ISM around most of the stars and tentatively identify it around the rest.
The discovery is exciting for many reasons, but not least because buckyballs are celebrities of the chemical world, beloved by students and trivia nuts far and wide.
After a couple of decades of theoretical predictions, the 60-atom molecules were finally discovered under laboratory conditions in 1985 by Robert Curl, Harold Kroto and Richard Smalley – for which they were eventually awarded a Nobel Prize.
The monster molecules were named after Richard Buckminster Fuller, an American architect and systems theorist who at the time had a prominent media profile because of his invention of building structures known as geodesic domes, which generally resembled the C60 structures. Buckminsterfullerene became, naturally enough, a buckyball.
Its confirmed presence, write Cordiner and colleagues in The Astrophysical Journal Letters, “represents a breakthrough in our understanding of chemical complexity in the diffuse ISM, dramatically increasing the size limit for known carbon-bearing molecules in low-density, strongly irradiated environments”.
It also, they add, brings a new understanding to the quest to identify the remaining, unidentified molecules that exist in the diffuse medium.