How stars are born. ALMA observes birth cry of a massive baby star
An international research team used the Atacama Large Millimetre/submillimeter Array (ALMA), an international research team observed a baby star and obtained clear evidence of rotation in the outflow. The motion and the shape of the outflow indicate that the interplay of centrifugal and magnetic forces in a disk surrounding the star plays a crucial role in the star’s birth cry.
The observations are important as scientists do not yet fully understand how it is possible to form the massive stars seen in space. The main issue is one regarding the rotation of gases. Stars form from gas and dust floating in interstellar space. The cloud of gas rotates faster as it shrinks due to self-gravity, but this would mean that stars should have a rapid rotation, a fact contradicted by astronomic observation.
Scientists are wondering how this rotational momentum is dissipated. One theory says that if the gas outflow rotates, it can carry rotational momentum away from the system. Astronomers have tried to detect the rotation of the outflow to test this scenario and understand its launching mechanism.
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The team of astronomers led by Tomoya Hirota, an assistant professor at the National Astronomical Observatory of Japan and the Graduate University for Advanced Studies observed a massive baby star called Orion KL Source I in the famous Orion Nebula, located 1,400 light-years away from the Earth. The Orion Nebula is the closest massive star-forming region to Earth. Thanks to its close vicinity and ALMA’s advanced capabilities, the team could reveal the nature of the outflow from the outer disk.
“We have clearly imaged the rotation of the outflow,” said Hirota, the lead author of the research paper published in the journal Nature Astronomy. “In addition, the result gives us important insight into the launching mechanism of the outflow.”
The observations strongly support the idea that the outflow plays an important role in dissipating the rotational energy. ALMA clearly shows that the outflow is launched not from the vicinity of the baby star itself, but rather from the outer edge of the disk. This morphology agrees well with the “magnetocentrifugal disk wind model.”
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