Possible planet formation in the young, low-mass, multiple stellar system GG Tau A

• Published in: Nature (London) Vol. 514; no. 7524; pp. 600 - 602
• Main Authors: Dutrey, Anne, Di Folco, Emmanuel, Guilloteau, Stéphane, Boehler, Yann, Bary, Jeff, Beck, Tracy, Beust, Hervé, Chapillon, Edwige, Gueth, Fredéric, Huré, Jean-Marc, Pierens, Arnaud, Piétu, Vincent, Simon, Michal, Tang, Ya-Wen
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 30-10-2014; Nature Publishing Group
• Subjects: 639/33/34/862; Accretion; Astronomical research; Astrophysics; Asymmetry; Carbon monoxide; Cosmology and Extra-Galactic Astrophysics; Dust; Humanities and Social Sciences; letter; multidisciplinary; Physics; Planet formation; Planets; Science; Sciences of the Universe; Star & galaxy formation; Stars; Stars, Double; Symmetry; Exoplanets
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature13822

Investigation of the triple stellar system GG Tau A reveals gas fragments within the central cavity between the Keplerian outer ring orbiting the entire system and the stars themselves; gas flow from this outer ring appears capable of sustaining the inner disk surrounding component star GG Tau Aa beyond the accretion lifetime, leaving time for planet formation to occur.
Possible planet formation in G GTau A
Atacama Large Millimetre Array (ALMA) observations of G GTau A, one of the most intensively studied stellar systems, reveal a flow of fresh material that would make planet formation possible even in the unstable environment of young binary star systems. This flow had previously been predicted by numerical simulation, but not confirmed observationally. New images show gas fragments traced by carbon monoxide emission within the GG Tau A cavity. Kinematic analysis suggests that the flow is capable of sustaining the inner disk around GG Tau Aa beyond the accretion lifetime, leaving sufficient time to allow planet formation.
The formation of planets around binary stars may be more difficult than around single stars
1
,
2
,
3
. In a close binary star (with a separation of less than a hundred astronomical units), theory predicts the presence of circumstellar disks around each star, and an outer circumbinary disk surrounding a gravitationally cleared inner cavity around the stars
4
,
5
. Given that the inner disks are depleted by accretion onto the stars on timescales of a few thousand years, any replenishing material must be transferred from the outer reservoir to fuel planet formation (which occurs on timescales of about one million years). Gas flowing through disk cavities has been detected in single star systems
6
. A circumbinary disk was discovered around the young low-mass binary system GG Tau A (ref.
7
), which has recently been shown to be a hierarchical triple system
8
. It has one large inner disk
9
around the single star, GG Tau Aa, and shows small amounts of shocked hydrogen gas residing within the central cavity
10
, but other than a single weak detection
11
, the distribution of cold gas in this cavity or in any other binary or multiple star system has not hitherto been determined. Here we report imaging of gas fragments emitting radiation characteristic of carbon monoxide within the GG Tau A cavity. From the kinematics we conclude that the flow appears capable of sustaining the inner disk (around GG Tau Aa) beyond the accretion lifetime, leaving time for planet formation to occur there. These results show the complexity of planet formation around multiple stars and confirm the general picture predicted by numerical simulations.