Modeling the Break in the Specific Angular Momentum within the Envelope–Disk Transition Zone
Year: 2026
Type: article
Abstract: The observations of protostellar systems show a transition in the radial profile of specific angular momentum (and rotational velocity), as evolving from j ∼ constant ( v ϕ ∼ r −1 ) in the infalling-rotating envelope to j ∝ r 1/2 ( v ϕ ∼ r −1/2 ) in the Keplerian disk. We employ global MHD disk simulations of gravitational collapse starting from a supercritical prestellar core, that forms a disk and envelope structure in a self-consistent manner, in order to determine the physics of the envelope–disk transition zone (E n DT ran Z). Our results show that the transition from the infalling-rotating envelope to Keplerian disk happens through a jump in the j − r profile, spanning over a finite radial width, which is characterized by the positive local gravitational torques. The outer edge of the E n DT ran Z is identified where the radial infall speed ( v r ) begins a sharp decline in magnitude and j begins a transition from j ∼ constant toward j ∼ r 1/2 . Moving radially inward, the centrifugal radius ( r CR ) is defined where v ϕ first transitions to Keplerian velocity at the disk’s edge. Farther inward of r CR , the model disk develops a super-Keplerian rotation due to self-gravity. The inner edge of E n DT ran Z is defined at model centrifugal barrier ( r CB ) where v r drops to negligible values. Inside r CB , a net negative gravitational torque drives mass accretion onto the protostar. On observational grounds, we identify a jump in the observed j − r profile of class 0/I protostar L1527 IRS for the first time using the ALMA Large Program Early Planet Formation in Embedded Disks (eDisk) data. Comparison with our numerical radial behavior suggests the observed j − r jump serves as a kinematical tracer for the existence of E n DT ran Z. Our results offer insights into the observable imprint of angular momentum redistribution mechanisms during star–disk formation.
Source: The Astrophysical Journal
Institutions: Institute of Astronomy and Astrophysics, Academia Sinica, Academia Sinica, Western University, University of Toronto, Canadian Institute for Theoretical Astrophysics, University of Vienna, Southern Federal University, Universität Innsbruck, Korea Astronomy and Space Science Institute, Korea University of Science and Technology
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
OpenAlex ID: W7154487696