Massive Stars Formed in a Gas Disk? Discovery of a Hot Circumstellar Disk around a Massive Protostar

A research team led by Tomoya Hirota (National Astronomical Observatory of Japan: NAOJ) discovered a hot circumstellar disk around a massive protostar by using the Atacama Large Millimeter/Submillimeter Array (ALMA) and the VLBI Exploration of Radio Astrometry (VERA), which is a Japanese very long baseline interferometer (VLBI) network operated by NAOJ. The formation process of a massive star has been a long-standing problem. The research results favor disk accretion for the formation of massive stars, similar to the formation of low to intermediate mass stars such as the Sun.

The team observed a radio source called Source I in Orion KL, the nearest massive star-forming region. ALMA detected radio signals from hot water vapor with high angular resolution. The gas temperature reaches around 3000 degrees Celsius. Combining this data with the data taken by VERA, the team confirmed that the hot gas containing water vapor is actually a circumstellar disk around Source I. Thanks to an accurate estimated distance to Source I based on VERA observations, the disk diameter can be estimated at about 80 times larger than the distance between the Sun and Earth.

 Figure 1
Artist’s concept of Source I


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