View of the sky around the multiple star system GG Tauri
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ALMA Examines Ezekiel-like “Wheel in a Wheel” of Dust and Gas
For the first time, researchers using
ALMA have detected a streamer of gas flowing from a massive outer disc
toward the inner reaches of a binary star system. This never-before-seen
feature may be responsible for sustaining a second, smaller disc of
planet-forming material that otherwise would have disappeared long ago.
Half of Sun-like stars are born in binary systems, meaning that these
findings will have major consequences for the hunt for exoplanets. The
results are published in the journal Nature on 30 October 2014.
A research group led by Anne Dutrey from the Laboratory of Astrophysics of Bordeaux, France and CNRS used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe the distribution of dust and gas in a multiple-star system called GG Tau-A [1]. This object is only a few million years old and lies about 450 light-years from Earth in the constellation of Taurus (The Bull).
Like a wheel in a wheel, GG Tau-A contains a large, outer disc
encircling the entire system as well as an inner disc around the main
central star. This second inner disc has a mass roughly equivalent to
that of Jupiter. Its presence has been an intriguing mystery for
astronomers since it is losing material to its central star at a rate
that should have depleted it long ago.
While observing these structures with ALMA, the team made the
exciting discovery of gas clumps in the region between the two discs.
The new observations suggest that material is being transferred from the
outer to the inner disc, creating a sustaining lifeline between the two
[2].
“Material flowing through the cavity was predicted by computer
simulations but has not been imaged before. Detecting these clumps
indicates that material is moving between the discs, allowing one to
feed off the other,” explains Dutrey. “These observations
demonstrate that material from the outer disc can sustain the inner disc
for a long time. This has major consequences for potential planet
formation.”
Planets are born from the material left over from star birth. This is
a slow process, meaning that an enduring disc is a prerequisite for
planet formation. If the feeding process into the inner disc now seen
with ALMA occurs in other multiple-star systems the findings introduce a
vast number of new potential locations to find exoplanets in the
future.
The first phase of exoplanet searches was directed at single-host stars like the Sun [3].
More recently it has been shown that a large fraction of giant planets
orbit binary-star systems. Now, researchers have begun to take an even
closer look and investigate the possibility of planets orbiting the
individual stars of multiple-star systems. The new discovery supports
the possible existence of such planets, giving exoplanet discoverers new
happy hunting grounds.
Emmanuel Di Folco, co-author of the paper, concludes: “Almost
half the Sun-like stars were born in binary systems. This means that we
have found a mechanism to sustain planet formation that applies to a
significant number of stars in the Milky Way. Our observations are a big
step forward in truly understanding planet formation.”
Notes
[1] GG Tau-A is part of a more complex multiple-star system called GG Tauri. Recent observations of GG Tau-A using the VLTI
have revealed that one of the stars — GG Tau Ab, the one not surrounded
by a disc — is itself a close binary, consisting of GG Tau-Ab1 and GG
Tau-Ab2. This introduced a fifth component to the GG Tau system.
[2] An earlier result with ALMA showed an example of a single star with material flowing inwards from the outer part of its disc.
[3] Because orbits in binary stars are more complex and less stable, it was believed that forming planets in these systems would be more challenging than around single stars.
[2] An earlier result with ALMA showed an example of a single star with material flowing inwards from the outer part of its disc.
[3] Because orbits in binary stars are more complex and less stable, it was believed that forming planets in these systems would be more challenging than around single stars.
More information
This research was presented in a paper
entitled “Planet formation in the young, low-mass multiple stellar
system GG Tau-A” by A. Dutrey et al., to appear in the journal Nature.
The team is composed of Anne Dutrey (University Bordeaux/CNRS,
France), Emmanuel Di Folco (University Bordeaux/CNRS), Stephane
Guilloteau (University Bordeaux/CNRS), Yann Boehler (University of
Mexico, Michoacan, Mexico), Jeff Bary (Colgate University, Hamilton,
USA), Tracy Beck (Space Telescope Science Institute, Baltimore, USA),
Hervé Beust (IPAG, Grenoble, France), Edwige Chapillon (University
Bordeaux/IRAM, France), Fredéric Gueth (IRAM, Saint Martin d’Hères,
France), Jean-Marc Huré (University Bordeaux/CNRS), Arnaud Pierens
(University Bordeaux/CNRS), Vincent Piétu (IRAM), Michal Simon (Stony
Brook University, USA) and Ya-Wen Tang (Academia Sinica Institute of
Astronomy and Astrophysics, Taipei, Taiwan).
The Atacama Large Millimeter/submillimeter Array (ALMA), an
international astronomy facility, is a partnership of Europe, North
America and East Asia in cooperation with the Republic of Chile. ALMA is
funded in Europe by the European Southern Observatory (ESO), in North
America by the U.S. National Science Foundation (NSF) in cooperation
with the National Research Council of Canada (NRC) and the National
Science Council of Taiwan (NSC) and in East Asia by the National
Institutes of Natural Sciences (NINS) of Japan in cooperation with the
Academia Sinica (AS) in Taiwan. ALMA construction and operations are led
on behalf of Europe by ESO, on behalf of North America by the National
Radio Astronomy Observatory (NRAO), which is managed by Associated
Universities, Inc. (AUI) and on behalf of East Asia by the National
Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory
(JAO) provides the unified leadership and management of the
construction, commissioning and operation of ALMA.
ESO is the foremost intergovernmental astronomy organisation in
Europe and the world’s most productive ground-based astronomical
observatory by far. It is supported by 15 countries: Austria, Belgium,
Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy,
the Netherlands, Portugal, Spain, Sweden, Switzerland and the United
Kingdom. ESO carries out an ambitious programme focused on the design,
construction and operation of powerful ground-based observing facilities
enabling astronomers to make important scientific discoveries. ESO also
plays a leading role in promoting and organising cooperation in
astronomical research. ESO operates three unique world-class observing
sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO
operates the Very Large Telescope, the world’s most advanced
visible-light astronomical observatory and two survey telescopes. VISTA
works in the infrared and is the world’s largest survey telescope and
the VLT Survey Telescope is the largest telescope designed to
exclusively survey the skies in visible light. ESO is the European
partner of a revolutionary astronomical telescope ALMA, the largest
astronomical project in existence. ESO is currently planning the
39-metre European Extremely Large optical/near-infrared Telescope, the
E-ELT, which will become “the world’s biggest eye on the sky”.
Links
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Contacts
Anne Dutrey
Laboratoire d'Astrophysique de Bordeaux / University Bordeaux/CNRS
France
Tel: +33 5 57 776140
Email: Anne.Dutrey@obs.u-bordeaux1.fr
Emmanuel DiFolco
Laboratoire d'Astrophysique de Bordeaux / University Bordeaux/CNRS
France
Tel: +33 5 57 776136
Email: Emmanuel.Difolco@obs.u-bordeaux1.fr
Richard Hook
ESO education and Public Outreach Department
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
