The team wants to learn the more detailed structure and dynamics of Source I by using ALMA with higher resolution and sensitivity at higher frequency. Such observations should reveal the mysteries of the evolution of Source I. Hirota said, “It is also important that the physical conditions of a circumstellar disk depend on the mass of the central protostar. The circumstellar disk around a massive star is heated up to 3000 degrees Celsius. Dust that is the material for planets should melt away at such high temperatures. I wonder if planets can form under such condition.
The team detected the two lines from the hot water molecules and clearly revealed the distribution. The distribution of the emissions from the 1700 degrees Celsius water molecules was similar to that of the jet observed via the SiO maser. The team interpreted this to mean that water molecules in the jet from Source I are emitting the radio maser.
The research team selected the nearest region of massive star-formation, Orion KL, for the ALMA observation. Stars with 8 times more mass than the Sun are forming in Orion KL. The distance to Orion KL is estimated to be about 1400 light-years, and it has been well studied since its discovery in 1967 because of its vicinity.
Thanks to recent intensive studies, the formation process of low to intermediate mass stars is now well understood. On the other hand, we know little about how massive stars form. Low and intermediate mass stars are formed by mass accretion from a circumstellar disk. Is this process the same for massive stars? Massive stars could form via stellar collisions as another theory suggests. We cannot answer such a simple question.
本研究は科学研究費補助金(21224002, 24540242, 24684011, 25108005, 25120007)、ALMA共同利用PIサポートプログラム(NAOJ-ALMA-0006)による補助を受けて行われました。
本研究は ”Hot Molecular Circumstellar Disk around the Massive Protostar Orion Source I” というタイトルで、The Astrophysical Journal Letters 782号、L28(2014年2月20日発行)に出版されました。
今回の研究を行ったチームのメンバーは、以下の通りです。