AsianScientist (Dec. 18, 2014) – Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) have unveiled the mechanism of the birth and growth of binary stars, found ubiquitously across the universe. The study documenting these findings has been published in The Astrophysical Journal.
Stars form in interstellar clouds of molecular gas and dust. Previous studies of star formation primarily focused on formation of single stars like the Sun, and a standard theory of single star formation has been established. In contrast, our understanding of binary star formation has been limited.
However, more than half of stars with a mass similar to that of the Sun are known to be binaries, making it crucial to unveil the physical mechanism of binary formation for a more comprehensive understanding of star formation.
Theoretically, a disk surrounding the “baby twin” stars is considered to feed materials to the central baby twin stars and grow them. While recent observations have found such disks surrounding the baby-twin stars, named “circumbinary disks”, those observations could not image the structures and gas motions of the disks to feed materials to the binary, because of the insufficient imaging resolution and sensitivity.
A team of, astronomers led by Shigehisa Takakuwa, Associate Research Fellow at the Institute of Astronomy and Astrophysics, Academia Sinica, found spiral arms of molecular gas and dust around the “baby twin” stars, binary protostars. Using the ALMA telescope, they observed the baby-twin star L1551 NE, located in the constellation of Taurus at a distance of 460 light years, with a 1.6 times better imaging resolution and a six times better sensitivity than those of their previous observations with the SubMillimeter Array (SMA).
“Our high-resolution ALMA observation has unveiled live images of the growth of the baby twins for the first time”, said Takakuwa.
They found a gas component associated with each binary star and a circumbinary disk surrounding both stars with a radius of 300 au, roughly to ten times the orbital radius of Neptune. For the first time, they succeeded in imaging the detailed structures of the circumbinary disk and found that the circumbinary disk consists of a southern U-shaped feature and northern emission protrusions pointing to the northwest and the northeast.
To understand these newly-identified features, the research team constructed a theoretical model of binary formation in L1551 NE using the supercomputer ATERUI at the National Astronomical Observatory of Japan (NAOJ). The southern U-shaped feature and northern emission protrusions observed with ALMA can be reproduced with a pair of spiral arms stemming from each baby twin.
The research team also investigated the observed gas motion as seen in the carbon monoxide molecular emission and identified faster rotating motions in the spiral arms and slower rotating motions in the inter-arm regions. The inter-arm regions also exhibit a falling gas motion toward the central baby twin stars, namely, the ongoing feeding process of the materials to the baby twin stars. These results show that the baby twin stars “shake” the surrounding circumbinary disk and induce the falling gas motion to feed the materials to the baby twin.
“We succeeded in unveiling structures and motions in the circumbinary disk with such a high accuracy, because of the high imaging resolution and sensitivity of ALMA,” explained Kazuya Saigo, co-principal investigator of the study.
“In this ALMA era, high-resolution ALMA observations coupled with thorough numerical simulations will be more and more important. Our research on L1551 NE using ALMA and theoretical modeling using a supercomputer can be regarded as an upcoming research trend”.
The article can be found at: Takakuwa et al. (2014) Angular Momentum Exchange by Gravitational Torques and Infall in the Circumbinary Disk of the Protostellar System L1551 NE.
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Source: National Astronomical Observatory of Japan.
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