Modelling the Break in the Specific Angular Momentum within the Envelope-Disk Transition Zone
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2026
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| author | Das, Indrani Basu, Shantanu Ohashi, Nagayoshi Vorobyov, Eduard Aso, Yusuke |
| author_facet | Das, Indrani Basu, Shantanu Ohashi, Nagayoshi Vorobyov, Eduard Aso, Yusuke |
| contents | The observations of protostellar systems show a transition in the radial profile of specific angular momentum (and rotational velocity), evolving from $j\sim{\rm constant}$ ($v_ϕ\sim r^{-1}$) in the infalling-rotating envelope to $j\propto r^{1/2}$ ($v_ϕ\sim r^{-1/2}$) 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 (ENDTRANZ). Our numerical results show the transition from the infalling-rotating envelope to Keplerian disk happens through a jump in the $j-r$ profile over a finite radial range, which is characterized by the positive local gravitational torques. The outer edge of the ENDTRANZ is identified where the radial infall speed ($v_r$) begins a sharp decline in magnitude and $j$ begins a transition from $j\sim{\rm constant}$ toward $j\sim r^{1/2}$. Moving radially inward, the centrifugal radius ($r_{\rm CR}$) is defined where $v_ϕ$ first transitions to Keplerian velocity at the disk's edge. Farther inward of $r_{\rm CR}$, model disk develops a super-Keplerian rotation due to self-gravity. The inner edge of the ENDTRANZ is defined at the centrifugal barrier ($r_{\rm CB}$) where $v_r$ drops to negligible values. Inside $r_{\rm CB}$, a net negative gravitational torque drives mass accretion onto the protostar. On observational grounds, we identify a jump in the observed $j-r$ profile in L1527 IRS for the first time using the ALMA eDisk data. Comparison with the numerical radial behavior from our MHD disk simulations suggests the observed $j-r$ jump can be used as a kinematical tracer for the existence of ENDTRANZ. Our results offer insights into the observable imprint of angular momentum redistribution mechanisms during star-disk formation. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2602_13683 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Modelling the Break in the Specific Angular Momentum within the Envelope-Disk Transition Zone Das, Indrani Basu, Shantanu Ohashi, Nagayoshi Vorobyov, Eduard Aso, Yusuke Solar and Stellar Astrophysics Earth and Planetary Astrophysics Astrophysics of Galaxies High Energy Astrophysical Phenomena The observations of protostellar systems show a transition in the radial profile of specific angular momentum (and rotational velocity), evolving from $j\sim{\rm constant}$ ($v_ϕ\sim r^{-1}$) in the infalling-rotating envelope to $j\propto r^{1/2}$ ($v_ϕ\sim r^{-1/2}$) 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 (ENDTRANZ). Our numerical results show the transition from the infalling-rotating envelope to Keplerian disk happens through a jump in the $j-r$ profile over a finite radial range, which is characterized by the positive local gravitational torques. The outer edge of the ENDTRANZ is identified where the radial infall speed ($v_r$) begins a sharp decline in magnitude and $j$ begins a transition from $j\sim{\rm constant}$ toward $j\sim r^{1/2}$. Moving radially inward, the centrifugal radius ($r_{\rm CR}$) is defined where $v_ϕ$ first transitions to Keplerian velocity at the disk's edge. Farther inward of $r_{\rm CR}$, model disk develops a super-Keplerian rotation due to self-gravity. The inner edge of the ENDTRANZ is defined at the centrifugal barrier ($r_{\rm CB}$) where $v_r$ drops to negligible values. Inside $r_{\rm CB}$, a net negative gravitational torque drives mass accretion onto the protostar. On observational grounds, we identify a jump in the observed $j-r$ profile in L1527 IRS for the first time using the ALMA eDisk data. Comparison with the numerical radial behavior from our MHD disk simulations suggests the observed $j-r$ jump can be used as a kinematical tracer for the existence of ENDTRANZ. Our results offer insights into the observable imprint of angular momentum redistribution mechanisms during star-disk formation. |
| title | Modelling the Break in the Specific Angular Momentum within the Envelope-Disk Transition Zone |
| topic | Solar and Stellar Astrophysics Earth and Planetary Astrophysics Astrophysics of Galaxies High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2602.13683 |