Researchers reveal how complex, massive stars are born

A new study has provided a deeper insight into the complex birth of the giant stars.

A research group led by Aya Higuchi, a researcher at Ibaraki University, conducted observations of the massive-star forming region IRAS 16547-4247 with the Atacama Large Millimeter/submillimeter Array (ALMA).

The observation results showed that the presence of multiple, or at least two, gas outflows from a protostar, indicating the possible existence of two new-born stars in this region. Also, the radio observation results of molecular line emission of methanol revealed in vivid detail an hourglass structure created by gas outflows spreading outward while thrusting the ambient gas cloud away.

It was the first time that such an hourglass structure was found in observations of methanol in high-mass star forming regions. Detailed observations of high-mass stars have been considered difficult so far because high-mass stars form in a complex environment with multiple protostars in clusters, and their forming regions are located farther away from the Earth compared to those of low-mass stars.

The observation results of CO indicates that the outflows which looked like a blurred object extending in the north-south direction was actually two pairs of outflows aligned with the north-south and east-west direction respectively. Since the angular resolution provided by ALMA was 36 times higher than that applied to the past CO observations.

The observation results clearly revealed the details of complex structure and kinematics of gas. As it is assumed that one protostar was able to produce only a pair of outflows, these results suggested that multiple stars are being formed simultaneously in this region.

On top of these, the research group discovered that methanol molecule was spreading from the center of IRAS1654-4247 in the form of hourglass structure. CH3OH was normally produced on the surface of dust, but when the temperature increases by some process, it would be released from the dust surface and turn into gas which emits radio waves.

Since the hourglass structure made by the distribution of CH3OH traces the contour of the observed CO outflow, CH3OH was assumed to have been produced by the interaction with the ambient gas which was pushed away by the outflow from the protostar, resulting in the increase of temperature and consequent transition into gas.

This kind of hourglass structure has often been found around low-mass protostars, but it was the first time that the distribution of CH3OH with this structure was found in a high-mass-star forming region.

Although it was unknown what was responsible for the maser source in this object, the observation results this time suggests that the maser source was excited by the shock influence between a high-velocity outflow and the ambient gas.