Astronomers Find Rare 5-Star System


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An illustration of two contacting stars — part of the newly discovered bizarre five-star system.

Scientists have discovered an absolutely bizarre star system about 250 light years away, in the constellation Ursa Major.

The system (officially known as 1SWASP J093010.78+533859.5) features five stars that are all gravitationally bound together. Two orbit each other in what’s called a contact eclipsing binary, meaning they’re so close together that they actually share an atmosphere, with gases flowing between them.

Another two stars also orbit each other, but at a much greater distance — about 1.8 million miles, which is more than twice the diameter of the sun. Another star hangs out near that pair, but doesn’t appear to orbit them.

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Systems that include five stars gravitationally bound together are rare, though not unprecedented (astronomers have actually found systems that include as many as six stars). But this is the first one ever found that includes multiple pairs of stars orbiting each other.

The discoverers of the strange system — a team of astronomers from Open University in the UK and elsewhere — presented all these discoveries in a new paper published in the journal Astronomy & Astrophysics. Thanks to George Dvorsky at io9 for bringing it to our attention.

Source: vox.com

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ALMA Identifies Gas Spirals as a Nursery of Twin Stars


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With new Atacama Large Millimeter/submillimeter Array (ALMA) observations, astronomers led by Shigehisa Takakuwa, Associate Research Fellow at the Institute of Astronomy and Astrophysics, Academia Sinica (ASIAA), Taiwan, have found spiral arms of molecular gas and dust around “baby twin” stars. Gas motions supplying materials to the twin were also identified. These results unveil for the first time, the mechanism of the birth and growth of binary stars, which are ubiquitous throughout the Universe. The study was published on November 20 in The Astrophysical Journal.

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Fig 1. Gas and dust disks around L1551 NE spotted by ALMA. Credit: ALMA (ESO/NAOJ/NRAO) / Takakuwa et al.

Stars form in interstellar clouds of molecular gas and dust. Previous studies of star formation focused primarily on single stars like the Sun, and a standard picture of single star formation has been established. According to this picture, a dense gas condensation in an interstellar cloud collapses gravitationally to form a single protostar at the center. Previous observations have found such collapsing gas motions feeding material toward the central protostars.

Compared to single star formation, our understanding of binary star formation has been limited, even though more than half of stars with a mass similar to that of the Sun are known to be binaries. It is thus crucial to observe the physical mechanism of binary formation to obtain a more comprehensive understanding of star formation. Theory suggests that a disk surrounding a young binary will feed material to the central “baby twin” in order for them to grow. While recent observations have found such disks (known as “circumbinary disks”), it was not possible to image the structure and gas motions because of the insufficient imaging resolution and sensitivity.

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Fig 2. Comparison of the disks in simulation and observation. The right panel shows the disk image simulated with ATERUI, and the left panel the real ALMA image. Credit: ALMA (ESO/NAOJ/NRAO)/ Takakuwa et al.

Continue reading ALMA Identifies Gas Spirals as a Nursery of Twin Stars

Planet-forming lifeline discovered in a binary star system


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Artist’s impression of the double-star system GG Tauri-A.

If the feeding process into the system’s inner disk occurs elsewhere, the findings introduce many new potential locations to find exoplanets.

For the first time, researchers using ALMA have detected a streamer of gas flowing from a massive outer disk toward the inner reaches of a binary star system. This never-before-seen feature may be responsible for sustaining a second, smaller disk 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.

A research group led by Anne Dutrey from the Laboratory of Astrophysics of Bordeaux, France, 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. This object is only a few million years old and lies about 450 light-years from Earth in the constellation Taurus the Bull.

Like a wheel in a wheel, GG Tau-A contains a large, outer disk encircling the entire system as well as an inner disk around the main central star. This second inner disk 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 disks. The new observations suggest that material is being transferred from the outer to the inner disk, 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 disks, allowing one to feed off the other,” said Dutrey. “These observations demonstrate that material from the outer disk can sustain the inner disk 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 a prerequisite for planet formation. If the feeding process into the inner disk 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. 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.

“Almost half the Sun-like stars were born in binary systems,” said Emmanuel Di Folco from the Laboratory of Astrophysics of Bordeaux, France. “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.”ast