For the first time, astronomers have detected a streamer of gas flowing from a massive outer disc of planet-forming material toward the inner, smaller disc of a double star system.
This artist’s impression shows the dust and gas around the binary star system GG Tauri-A. Image credit: ESO / L.Calçada.
The star system in question, GG Tauri-A, is part of a more complex multiple-star system called GG Tauri.
It is only a few million years old and lies about 450 light-years from Earth in the constellation of Taurus.
Like the Old Testament prophet Ezekiel’s wheel in a wheel, GG Tauri-A contains a large, outer disc encircling the entire system as well as an inner disc around the main central star.
The 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 the Atacama Large Millimeter/submillimeter Array, the team headed by Dr Anne Dutrey of the Laboratory of Astrophysics in Bordeaux, France, made the 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.
“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,” said Dr Dutrey, who is the first author of a paper published in the journal Nature.
“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 disk is needed for planet formation.
If this same feeding process occurs in other multiple-star systems, the ALMA observations may explain the frequency with which planets have been and continue to be discovered in double systems.
“We may be witnessing these types of exoplanetary systems in the midst of formation. In a sense, we are learning why these seemingly strange systems exist,” said co-author Dr Jeffrey Bary of Colgate University in Hamilton, NY.
The first phase of exoplanet searches was directed at single host-stars like the Sun, more recently it has been shown that a large fraction of giant planets orbit binary star systems.
Now, astronomers have begun to take an even closer look and investigate the possibility of planets orbiting individual stars of multiple-star systems.
The new discovery supports the possible existence of such planets, marking a new era in the hunt for exoplanets.
“This means that multiple star systems have a way to form planets, despite their complicated dynamics. Given that we continue to find interesting planetary systems, our observations provide a glimpse of the mechanisms that enable such systems to form,” Dr Bary said.
“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,” said co-author Dr Emmanuel Di Folco of the University of Bordeaux, France.
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Anne Dutrey et al. 2014. Possible planet formation in the young, low-mass, multiple stellar system GG Tau A. Nature 514, 600–602; doi: 10.1038/nature13822
