Massive gas disk raises questions about planet formation theory


IMAGE: The circulation of dust is displayed in red; the circulation of carbon monoxide gas is displayed in green; and the circulation of carbon atoms is displayed in blue.
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Credit: ALMA (ESO/NAOJ/NRAO), Higuchi et al.

Astronomers utilizing the Atacama Large Millimeter/submillimeter Array (ALMA) discovered a young star surrounded by an amazing mass of gas. The star, called 49 Ceti, is 40 million years of ages and traditional theories of planet formation forecast that the gas need to have vanished by that age. The enigmatically big quantity of gas demands a reconsideration of our present understanding of planet formation.

Planets are formed in gaseous dirty disks called protoplanetary disks around young stars. Dust particles aggregate together to form Earth-like worlds or to end up being the cores of more massive worlds by gathering big quantities of gas from the disk to form Jupiter-like gaseous huge worlds. According to present theories, as time passes the gas in the disk is either included into worlds or blown away by radiation pressure from the main star. In the end, the star is surrounded by worlds and a disk of dirty particles. This dirty disk, called a particles disk, suggests that the planet formation procedure is practically completed.

Recent advances in radio telescopes have actually yielded a surprise in this field. Astronomers have actually discovered that a number of particles disk still have some quantity of gas. If the gas stays long in the particles disks, planetary seeds might have adequate time and product to progress to huge worlds like Jupiter. For that reason, the gas in a particles disk impacts the structure of the resultant planetary system.

“We found atomic carbon gas in the debris disk around 49 Ceti by using more than 100 hours of observations on the ASTE telescope,” states Aya Higuchi, an astronomer at the National Astronomical Observatory of Japan (NAOJ). ASTE is a 10-m size radio telescope in Chile run by NAOJ. “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.”

Thanks to ALMA’s high resolution, the group exposed the spatial circulation of carbon atoms in a particles disk for the very first time. Carbon atoms are more extensively dispersed than carbon monoxide gas, the 2nd most plentiful particles around young stars, hydrogen particles being the most plentiful. The quantity of carbon atoms is so big that the group even spotted faint radio waves from a rarer kind of carbon, 13C. This is the very first detection of the 13C emission at 492 GHz in any huge things, which is generally concealed behind the emission of typical 12C.

“The amount of 13C is only 1% of 12C, therefore the detection of 13C in the debris disk was totally unexpected,” states Higuchi. “It is clear evidence that 49 Ceti has a surprisingly large amount of gas.”

What is the origin of the gas? Scientists have actually recommended 2 possibilities. One is that it is remnant gas that made it through the dissipation procedure in the last stage of planet formation. The quantity of gas around 49 Ceti is, nevertheless, similar to those around much more youthful stars in the active planet formation stage. There are no theoretical designs to describe how a lot gas might have continued for so long. The other possibility is that the gas was launched by the crashes of little bodies like comets. However the variety of crashes required to describe the big quantity of gas around 49 Ceti is too big to be accommodated in present theories. Today ALMA results trigger a reconsideration of the planet formation designs.


The research study staff member are:
Aya Higuchi (National Astronomical Observatory of Japan), Yoko Oya (The University of Tokyo), Kazuya Saigo (National Astronomical Observatory of Japan), Hiroshi Kobayashi (Nagoya University), Kazunari Iwasaki (National Astronomical Observatory of Japan), Munetake Momose (Ibaraki University), Kang Lou Soon (Ibaraki University), Nami Sakai (RIKEN), Masanobu Kunitomo (Kurume University), Daisuke Ishihara (Japan Space Exploration Agency), and Satoshi Yamamoto (The University of Tokyo)

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