Astronomers using the Atacama Large Millimeter/Submillimeter Array (ALMA) have detected gas-phase methanol (methyl alcohol) in the protoplanetary disc around the young, Sun-like star TW Hydrae.
This artist’s impression shows the closest known protoplanetary disc, around the star TW Hydrae. The organic molecule methanol has been found by ALMA in this disc. This is the first such detection of the compound in a young planet-forming disc. Image credit: M. Kornmesser / ESO.
Otherwise known as HIP 53911 and IRAS 10594-3426, TW Hydrae is an orange dwarf star located in the constellation Hydra, approximately 124 light-years away.
The star is about 55% of the mass of the Sun and is very young – only 8 million years old.
The protoplanetary disc around TW Hydrae is the closest known example to Earth. As such it is an ideal target for astronomers to study discs.
A team of scientists led by Leiden Observatory astronomer Catherine Walsh has used ALMA to investigate the chemistry of TW Hydrae’s disk.
The observations have revealed the fingerprint of gaseous methanol (CH3OH) in a protoplanetary disc for the first time.
“Finding methanol in a protoplanetary disc shows the unique capability of ALMA to probe the complex organic ice reservoir in discs and so, for the first time, allows us to look back in time to the origin of chemical complexity in a planet nursery around a young Sun-like star,” Dr. Walsh said.
According to scientists, methanol is one of the largest complex organic molecules detected in discs to date. Identifying its presence in pre-planetary objects represents a milestone for understanding how organic molecules are incorporated into nascent planets.
Furthermore, this organic molecule is itself a building block for more complex species of fundamental prebiotic importance, like amino acid compounds.
The sharp vision of ALMA has also allowed the team to map the gaseous methanol across the TW Hydrae disc.
They discovered a ring-like pattern in addition to significant emission from close to the central star.
“A ring of methanol between 30 and 100 AU reproduces the pattern of the observed methanol data,” the scientists explained.
“The identified structure supports the hypothesis that the bulk of the disc ice reservoir is hosted primarily on the larger dust grains, residing in the inner 50 AU, which have become decoupled from the gas, and drifted radially inwards towards the star.”
“Methanol in gaseous form in the disc is an unambiguous indicator of rich organic chemical processes at an early stage of star and planet formation,” said co-author Dr. Ryan A. Loomis
“This result has an impact on our understanding of how organic matter accumulates in very young planetary systems.”
The results were published in the May 20 issue of the Astrophysical Journal Letters.
_____
Catherine Walsh et al. 2016. First detection of gas-phase methanol in a protoplanetary disk. ApJ 823, L10; doi: 10.3847/2041-8205/823/1/L10
