We report on the first bird ’ s-eye view of the innermost accretion disk around the high-mass protostellar object G353.273+0.641 , taken by Atacama Large Millimter/submillimeter Array long-baselines .
The disk traced by dust continuum emission has a radius of 250 au , surrounded by the infalling rotating envelope traced by thermal CH _ { 3 } OH lines .
This disk radius is consistent with the centrifugal radius estimated from the specific angular momentum in the envelope .
The lower-limit envelope mass is \sim 5-7 M _ { \sun } and accretion rate onto the stellar surface is 3 \times 10 ^ { -3 } M _ { \sun } yr ^ { -1 } or higher .
The expected stellar age is well younger than 10 ^ { 4 } yr , indicating that the host object is one of the youngest high-mass objects at present .
The disk mass is 2-7 M _ { \sun } , depending on the dust opacity index .
The estimated Toomre ’ s Q parameter is typically 1-2 and can reach 0.4 at the minimum .
These Q values clearly satisfy the classical criteria for the gravitational instability , and are consistent with the recent numerical studies .
Observed asymmetric and clumpy structures could trace a spiral arm and/or disk fragmentation .
We found that 70 \% of the angular momentum in the accretion flow could be removed via the gravitational torque in the disk .
Our study has indicated that the dynamical nature of a self-gravitating disk could dominate the early phase of high-mass star formation .
This is remarkably consistent with the early evolutionary scenario of a low-mass protostar .