Keplerian-Like Disk around the O-Type Star AFGL 4176

Massive stars with more than 8 times the mass of the Sun form so rapidly that even after formation, they can still remain deeply embedded in their natal envelopes of gas and dust. This makes it difficult to observe whether high-mass stars that are still in the process of forming can have stable Keplerian disks of material. Using the Atacama Large Millimeter/submillimeter Array (ALMA) to peer through the gas and dust, Johnston et al. (2015) present the discovery of a Keplerian-like disk around the still-forming O-type star AFGL 4176.

The disk of material around AFGL 4176 is estimated to have a radius of roughly 2000 AU. The inner radius of the disk is predicted to be 31.3 AU, because any closer to the massive protostar, temperatures become high enough for dust grains to sublimate. The total mass of gas in the disk is predicted to be ~12 times the mass of the Sun.

At the center of the Keplerian-like disk lies the still-forming O-type star AFGL 4176. The mass of AFGL 4176 is estimated to be ~25 times the mass of the Sun. Also, AFGL 4176 is predicted to have an effective temperature of roughly 36,900 K and almost 7 times the Sun’s radius. The disk of material around AFGL 4176 is currently the best example of a disk in Keplerian-like rotation around a forming O-type star.

Reference:
Johnston et al. (2015), “A Keplerian-like disk around the forming O-type star AFGL 4176”, arXiv:1509.08469 [astro-ph.SR]