Planet-forming stream found in binary star system
Planet-forming stream found in binary star system
Oct 31, 2014
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Feeding planets: artist's impression of GG Tau A
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Astronomers using the ALMA array of radio telescopes in Chile are the first to see a streamer of gas and dust flowing towards a single star in a binary system. This material is crucial for sustaining the formation of planets, and the observation could explain how planets can form around single stars in a binary system – something that had puzzled astronomers. This has important implications for astronomers studying planets outside of the solar system, because almost half of the Sun-like stars that we know of were formed in binary systems.
Astronomers have so far discovered more than 1800 planets orbiting stars other than the Sun. One striking thing about these exosolar planets – or exoplanets – is that they exist in a variety of systems, many of which are very different to our own solar system and include binary star systems. Sometimes planets in binary systems orbit both stars, and follow large "circumbinary" orbits. In other cases, planets will orbit tightly around one of the stars in a binary system.
Creation mystery
It is this latter case that has puzzled astronomers, because it is not clear how such planets could form. The mystery is illustrated nicely by the subject of this latest study: a young system called GG Tau A that is 450 million light-years away, and actually comprises three stars. Two of the stars orbit each other tightly, and a third star is some distance away. As a result, the third star (called GG Tau Aa) can essentially be thought of as one half of a binary system.
The system is surrounded by a large outer disc of dust and gas that orbits all three of the stars. One of its stars – GG Tau Aa – is also surrounded by its own compact inner disc of dust and gas, with a total mass on par with that of Jupiter. There is very little dust and gas in the large gap between the inner disc and outer disc, because the competing gravitational forces of the stars prevent matter from accumulating in this intermediate region.
More:
http://physicsworld.com/cws/article/news/2014/oct/31/planet-forming-stream-found-in-binary-star-system
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