The Role of Non-ionizing Radiation Pressure in Star Formation: The Stability of Cores and Filaments

TL;DR

This paper investigates how non-ionizing radiation pressure influences the stability of molecular cloud cores and filaments, revealing that irradiation can trigger star formation by lowering collapse thresholds.

Contribution

It introduces a hydrostatic, isothermal model to quantify how interstellar radiation pressure affects gravitational stability of dense structures, a factor previously less considered.

Findings

Radiation pressure lowers critical mass and line density for collapse.

Interstellar irradiation significantly influences star formation thresholds.

Effects are notable even without ionizing radiation sources.

Abstract

Stars form when filaments and dense cores in molecular clouds fragment and collapse due to self-gravity. In the most basic analyses of gravitational stability, the competition between self-gravity and thermal pressure sets the critical (i.e. maximum stable) mass of spheres and the critical line density of cylinders. Previous work has considered additional support from magnetic fields and turbulence. Here, we consider the effects of non-ionizing radiation, specifically the inward radiation pressure force that acts on dense structures embedded in an isotropic radiation field. Using hydrostatic, isothermal models, we find that irradiation lowers the critical mass and line density for gravitational collapse, and can thus act as a trigger for star formation. For structures with moderate central densities, $\sim10^3$ cm$^{-3}$, the interstellar radiation field in the Solar vicinity has an order unity effect on stability thresholds. For more evolved objects with higher central densities, a significant lowering of stability thresholds requires stronger irradiation, as can be found closer to the Galactic center or near stellar associations. Even when strong sources of ionizing radiation are absent or extincted, our study shows that interstellar irradiation can significantly influence the star formation process.