Oral Presentation
From Infall to Keplerian Rotation: The Envelope–Disk Transition Zone (EnDTranZ) in Star and Disk Formation
Presenter: Indrani Das (Academia Sinica Institute of Astronomy & Astrophysics (ASIAA))
Protoplanetary disks form around young stars when dense molecular cloud cores collapse. An outer shroud of gas and dust, known as the envelope, surrounds and feeds both the young star and the forming disk. The observations of protostellar systems show a break in the radial profile of specific angular momentum (and in the rotational velocity), as evolving from the envelope to the Keplerian disk. In this talk, I will present our results based on both theoretical and observational grounds, that show the existence of a distinct transition zone at the envelope-disk interface, through which infalling gas motions from the envelope transforms into keplerian motions within the disk. We name this transition zone at the envelope-disk interface as ENDTRANZ (Envelope Disk Transition Zone). We first employ global MHD disk simulations of gravitational collapse starting from a starless cloud core, in order to self-consistently determine the physics of the ENDTRANZ. Our simulations reveal that the transition from the infalling-rotating envelope to the Keplerian disk gradually unfolds through a jump across a finite thickness in the radial profile of specific angular momentum. This jump serves as a kinematical tracer for the angular momentum redistribution within ENDTRANZ and suggests how the internal torques play a key role in shaping up disk formation. We also, for the first time, identify a similar jump, in the radial profile of the specific angular momentum at the envelope-disk transition of class 0/I protostar L1527 IRS, using ALMA Large Program eDisk (Embedded Disks in Planet Formation) observations. This observed jump, spanning a measurable radial width, confirms the existence of the ENDTRANZ in L1527 IRS. Our results offer insights into the observable imprints of the overall mass and angular momentum redistribution during star–disk formation.
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