"The disks around young stars are the places where planets will be formed," said Yusuke Aso, of the University of Tokyo and lead author of a paper published in the Astrophysical Journal. "To understand the formation mechanism of a disk, we need to differentiate the disk from the outer envelope precisely and pinpoint the location of its boundary."
ANALYSIS: ALMA: Extreme, High Precision Astronomy in the Desert
Zooming in on a protostar named TMC-1A, which is located around 450 light-years away in the constellation Taurus, Aso's team were able to see its spinning inner disk (the protoplanetary disk) and differentiate it from the cloud feeding it. ALMA's extreme precision at measuring velocity distributions was key to this endeavor.
In the case of TMC-1A, the transition boundary from spinning disk to surrounding gas cloud envelope was measured to extend 90 AU (astronomical units; where 1 AU is the average distance the Earth orbits the sun) from the central baby star, a distance 3-times bigger than the orbit of Neptune. What's more, the ALMA observations revealed the protostar's disk obeys Keplarian motion; the material closest to the star orbits faster, whereas the material further out orbits slower.