We report ALMA observations in 0.87 mm continuum and ^ { 12 } CO ( J = 3–2 ) toward a very low-luminosity ( < 0.1 L _ { \odot } ) protostar , which is deeply embedded in one of the densest core MC27/L1521F , in Taurus with an indication of multiple star formation in a highly dynamical environment .
The beam size corresponds to \sim 20 AU , and we have clearly detected blueshifted/redshifted gas in ^ { 12 } CO associated with the protostar .
The spatial/velocity distributions of the gas show there is a rotating disk with a size scale of \sim 10 AU , a disk mass of \sim 10 ^ { -4 } M _ { \odot } and a central stellar mass of \sim 0.2 M _ { \odot } .
The observed disk seems to be detached from the surrounding dense gas , although it is still embedded at the center of the core whose density is \sim 10 ^ { 6 } cm ^ { -3 } .
The current low-outflow activity and the very low luminosity indicate that the mass accretion rate onto the protostar is extremely low in spite of a very early stage of star formation .
We may be witnessing the final stage of the formation of \sim 0.2 M _ { \odot } protostar .
However , we can not explain the observed low luminosity with the standard pre-main-sequence evolutionary track unless we assume cold accretion with an extremely small initial radius of the protostar ( \sim 0.65 R _ { \odot } ) .
These facts may challenge our current understanding of the low mass star formation , in particular the mass accretion process onto the protostar and the circumstellar disk .