Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have detected radio emission from two carbon isotopes (12C and 13C) in a huge gas-rich debris disk around 49 Ceti, a 40-million-year-old star located 186 light-years away in the constellation of Cetus.
An artist’s impression of the gas-rich debris disk around 49 Ceti. Image credit: NAOJ.
“We found atomic carbon gas in the debris disk around 49 Ceti by using more than 100 hours of observations with ASTE, a 10-m diameter radio telescope in Chile,” explained Dr. Aya Higuchi, an astronomer at the National Astronomical Observatory of Japan.
“As a natural extension, we used ALMA to obtain a more detailed view, and that gave us the second surprise.”
“The carbon gas around 49 Ceti turned out to be 10 times more abundant than our previous estimation.”
Composite ALMA image of the gas-rich debris disk around the young star 49 Ceti. The distribution of dust is shown in red; the distribution of carbon monoxide is shown in green; and the distribution of carbon atoms is shown in blue. Image credit: ALMA / ESO / NAOJ / NRAO / Higuchi et al.
The amount of atomic carbon gas was so high that Dr. Higuchi and her colleagues detected radio signal not only from the normal isotope 12C but also from the much rarer form 13C.
“This is the first detection of the 13C emission at 492 GHz in any astronomical object, which is usually hidden behind the emission of normal 12C,” they said.
“The amount of 13C is only 1% of 12C, therefore the detection of 13C in the debris disk was totally unexpected,” Dr. Higuchi said.
“It is clear evidence that 49 Ceti has a surprisingly large amount of gas.”
The astronomers offered two possible explanations for the origin of this carbon gas.
“One is that it is remnant gas that survived the dissipation process in the final phase of planet formation,” they said.
“The amount of gas around 49 Ceti is, however, comparable to those around much younger stars in the active planet formation phase.”
“There are no theoretical models to explain how so much gas could have persisted for so long.”
“The other possibility is that the gas was released by the collisions of small bodies like comets. But the number of collisions needed to explain the large amount of gas around 49 Ceti is too large to be accommodated in current theories.”
The findings appear in the Astrophysical Journal Letters.
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Aya E. Higuchi et al. 2019. First Detection of Submillimeter-wave [13C i]3P1–3P0 Emission in a Gaseous Debris Disk of 49 Ceti with ALMA. ApJL 885, L39; doi: 10.3847/2041-8213/ab518d
