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Title: When and How Do Prestellar Cores Collapse? Critical Conditions and Collapse Dynamics from Analytic Modeling and Numerical Simulations

Speaker: Dr. Sanghyuk Moon (Princeton University)

Date&Time: 2024-06-20, 11:00 AM

Location: Science Hall 638

Talk to be delivered in English
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Abstract: Dense prestellar cores are roughly spherical, compact (< 0.1 pc), centrally-concentrated objects found at the bottom of the hierarchy of interstellar medium (ISM) structure. They are believed to be the immediate precursors of individual stars or stellar systems. Understanding the physical processes responsible for their formation and evolution is a necessary, but not sufficient, first step toward developing a theory that can predict the rate of star formation and the mass distribution of stars under the widely varying physical conditions that modern telescopes are beginning to probe. While the spherical collapse from an initially quasi-static prestellar core has been a classic problem studied since the 1960s, recent numerical simulations highlight the dynamic nature of their formation and evolution within a supersonically turbulent molecular cloud. Despite progress using various techniques, details remain unclear regarding the physical mechanisms responsible for the formation of dense cores and their evolution to the point of instability and collapse/star formation - or, alternatively, evolution resulting in dispersal. In this talk, I will present the results of our recent study addressing this problem. The basis of our analysis is tracking the evolution of individual "cores" forming in a suite of numerical simulations of an idealized molecular cloud. The core tracking procedure allows us to monitor the time variations of the key physical properties in and around the core, including the gravitational potential structure that effectively determines the outer "tidal boundary." To explain the emergent density and velocity structures of the simulated cores, we construct a semi-analytic model of turbulent equilibrium spheres (TESs) characterized by a power-law linewidth-size relation, in which the Bonnor-Ebert sphere naturally appears as a limiting solution with vanishing turbulent velocities. Considering the stability of TES and the tidal boundary set by surrounding structures, we propose a critical condition and a collapse scenario and test them using our numerical simulations - this constitutes the "When" in the title. Regarding the "How," I will discuss the timescales and collapse dynamics quantified by directly measured radial forces in an angle-averaged, quasi-Lagrangian equation of motion. I will conclude with remarks on potential observational implications.