V883 Orionis is a young star located approximately 1,300 light-years away in the constellation Orion. This star is experiencing a so-called FU Orionis type outburst, a sudden increase of luminosity due to a bursting torrent of material flowing from the protoplanetary disk to the star. This rare event has allowed Atacama Large Millimeter/submillimeter Array (ALMA) to detect five complex organic molecules — methanol, acetone, acetonitrile, acetaldehyde and methyl formate — in the disk around V883 Orionis.
An artist’s impression of the protoplanetary disk around the young star V883 Orionis. Image credit: National Astronomical Observatory of Japan.
Various molecules are frozen in ice around micrometer-sized dust particles in protoplanetary disks around infant stars.
V883 Orionis’ sudden flare-up is heating the disk and sublimating the ice, which releases the molecules into gas.
The region in a disk where the temperature reaches the sublimation temperature of the molecules is called the ‘snow line.’
The radii of snow lines are about a few AU (astronomical units) around normal young stars, however, they are enlarged almost 10 times around bursting stars.
False-color image of V883 Orionis taken with ALMA. The distribution of dust is shown in orange and the distribution of methanol is shown in blue. Image credit: ALMA / ESO / NAOJ / NRAO / Lee et al.
“It is difficult to image a disk on the scale of a few AU with current telescopes,” said Dr. Jeong-Eun Lee, an astronomer at Kyung Hee University.
“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.”
Thanks to ALMA’s sharp vision and the enlarged snow line due to the flare-up of the star, Dr. Lee and co-authors detected and analyzed five different complex organic molecules: methanol (CH3OH), acetone (CH3COCH3), acetaldehyde (CH3CHO), methyl formate (CH3OCHO), and acetonitrile (CH3CN).
Schematic illustration of the composition of protoplanetary disks in normal state and outburst phase. Image credit: National Astronomical Observatory of Japan.
The astronomers also obtained the spatial distribution of methanol and acetaldehyde.
“The distribution of these molecules has a ring-like structure with a radius of 60 AU, which is twice the size of Neptune’s orbit,” they said.
“Inside of this ring the molecules are invisible because they are obscured by thick dusty material, and are invisible outside of this radius because they are frozen in ice.”
“Since rocky and icy planets are made from solid material, the chemical composition of solids in disks is of special importance,” said Dr. Yuri Aikawa, an astronomer at the University of Tokyo.
“An outburst is a unique chance to investigate fresh sublimates, and thus the composition of solids.”
The findings were published in the journal Nature Astronomy.
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Jeong-Eun Lee et al. The ice composition in the disk around V883 Ori revealed by its stellar outburst. Nature Astronomy, published online February 4, 2019; doi: 10.1038/s41550-018-0680-0
