Ring Of Organic Molecules Discovered Around Outbursting Star

Artist’s impression of the protoplanetary disk around young star V883 Ori. National Astronomical Observatory of Japan

Researchers have discovered that an outburst from a young star is liberating complex organic molecules trapped inside the dusty icy disk surrounding it. The molecules found around this star include methanol, methyl formate, and even acetone. This is the first unequivocal observation of acetone in the planet-forming region of a star.

The chemical composition of the protoplanetary disk is similar to the comets of the Solar System, and researchers hope that this study, published in Nature Astronomy, will help us understand the evolution of organic compounds around both stars and planets. The star studied by the team is V883 Ori, which is located 1,300 light-years from Earth. What makes it both special and perfect for this study is the fact that it is experiencing an outburst that's pushing its snow line, the region where the disk’s dust is frozen further out.

Usually, the snow line is within a handful of astronomical units (AU) from the star (1 AU is the Earth-Sun distance). But around this special object, many more ice particles are sublimating and liberating organic molecules thanks to the outburst. And, as they are very spread out, they are finally visible to our instruments.

“It is difficult to image a disk on the scale of a few AU with current telescopes,” lead author Jeong-Eun Lee, from Kyung Hee University, said in a statement. “However, around an outburst star, ice melts in a wider area of the disk and it is easier to see the distribution of molecules. We are interested in the distribution of complex organic molecules as the building blocks of life.”

False-color image of V883 Ori taken with ALMA. The distribution of dust is shown in orange and the distribution of methanol, an organic molecule, is shown in blue. ALMA (ESO/NAOJ/NRAO), Lee et al.

The team used the powerful Atacama Large Millimeter/submillimeter Array (ALMA) and were able to track the distribution of methanol. The molecule forms a ring around the star with a radius of 60 AU, twice the size of Neptune’s orbit. The ring shape is important. Inside the ring, the organic molecules are obscured by the thick dusty materials that can lead to the formation of planets. Outside, they remain trapped in ice.

“Since rocky and icy planets are made from solid material, the chemical composition of solids in disks is of special importance. An outburst is a unique chance to investigate fresh sublimates, and thus the composition of solids,” explained Yuri Aikawa at the University of Tokyo, a member of the research team.

There are still many uncertainties about how life came to be and whether comets carrying organic molecules played a major role. The answers could be found around stars like V883 Ori.

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