2022.05.26 - Enrique Vázquez-Semadeni
Channel: Coloquio IRyA
Date: 27/05/2022

Speaker info: Dr. Enrique Vázquez-Semadeni, IRyA-UNAM
https://www.irya.unam.mx/web/en/people/research-staff/e-vazquez

Title: Revisiting spherical gravitational collapse
Abstract:
I will revisit the hypotheses leading to the classical quasi-static prestellar evolution for dense cores, followed by inside-out collapse during the protostellar stage. These hypotheses appear virtually unrealizable in practice, and when more realistic initial conditions are considered, the actual prestellar evolution should be closer to the dynamic ""early path"" solution of Whitworth & Summers 1985, for which the infall speed decreases to zero at the core's center. Synthetic observations of simulations of this regime of collapse suggest that traditional methods of inferring the infall speed systematically underestimate it by factors of a few, sufficient to make a supersonic flow to appear subsonic.
I will then describe a model for the dynamic evolution of the density profile from the onset of collapse to the formation of a protostar, showing that its logarithmic slope approaches a value of -2, and that, for slopes shallower than -2, the radial dependence of the mass accretion rate implies that the core accumulates mass, allowing it to grow. Most observed cores show slopes shallower than -2. Also, there is always an inner part of the core that is locally Jeans-stable, and grows by the compression of the outer parts. This suggests that apparently ""pressure-confined"" cores may actually be undergoing collapse even if they appear Jeans-stable, if they are the tip of a larger-scale collapsing cloud. Similarly, in the magnetic case, there is always aninner part that is always magnetically subcritical, but is compressed bythe outer supercritical parts.

I will then describe a model for the dynamic evolution of the density profile from the onset of collapse to the formation of a protostar, showing that its logarithmic slope approaches a value of -2, and that, for slopes shallower than -2, the radial dependence of the mass accretion rate implies that the core accumulates mass, allowing it to grow. Most observed cores show slopes shallower than -2. Also, there is always an inner part of the core that is locally Jeans-stable, and grows by the compression of the outer parts. This suggests that apparently ""pressure-confined"" cores may actually be undergoing collapse even if they appear Jeans-stable, if they are the tip of a larger-scale collapsing cloud. Similarly, in the magnetic case, there is always an inner part that is always magnetically subcritical, but is compressed by the outer supercritical parts.