Gravitational collapse revisited (Enrique Vázquez-Semadeni, IRyA-UNAM Morelia) скачать в хорошем качестве

Gravitational collapse revisited (Enrique Vázquez-Semadeni, IRyA-UNAM Morelia)

Classical Newtonian gravitational collapse is often envisioned as a spherical, homologous contraction that happens locally, all at once, and in isolation. However, this is an extremely unrealistic picture. Here I review the main features of realistic collapse: 1. Spherical collapse is non-homologous. This implies that the collapse does not occur at once, but rather develops a continuous accretion flow from low to high densities. 2. The collapse consists of a pre-singularity (prestellar) stage and a post-singularity (protostellar) one, each characterized by different density profiles and accretion regimes. 3. The prestellar stage occurs from the outside-in on scales smaller than the initial Jeans length. 4. At early times or large radii, the radial profile of the accretion rate depends on that of the density. The $r^{-2}$ radial density profile is an attractor, and corresponds to a radius-independent accretion rate. Shallower density profiles imply an inwards-decreasing accretion rate, and therefore an increasing gas mass. We refer to this process as "gravitational choking". 5. Non-spherical collapse amplifies anisotropies, and therefore generates a directional accretion flow, which produces a hierarchy of roundish, flattened and filamentary structures. Thus, filamentary accretion can be a signature of large-scale, gravity-driven accretion flow. 6. In the presence of initial turbulent density fluctuations, high-mass fluctuations of typical amplitude initiate their collapse earlier, but take longer times to conclude it than low-mass ones, so that the latter culminate their collapse first. This implies that, at early times, the small-scale regions in multi-center collapse flows appear super-virial, and later appear virialized.