Far and extreme ultraviolet radiation fields and consequent disc destruction in star-forming regions

Abstract

The first stages of planet formation usually occur when the host star is still in a (relatively) dense star-forming region, where the effects of the external environment may be important for understanding the outcome of the planet formation process. In particular, star-forming regions that contain massive stars have strong far-ultraviolet (FUV) and extreme ultraviolet (EUV) radiation fields, which can induce mass-loss from protoplanetary discs due to photoevaporation. In this paper, we present a parameter-space study of the expected FUV and EUV fields in N-body simulations of star-forming regions with a range of initial conditions. We then use recently published models to determine the mass-loss due to photoevaporation from protoplanetary discs. In particular, we focus on the effects of changing the initial degree of spatial structure and initial virial ratio in the star-forming regions, as well as the initial stellar density. We find that the FUV fields in star-forming regions are much higher than in the interstellar medium, even when the regions have stellar densities as low as in the Galactic field, due to the presence of intermediate-mass, and massive, stars (>5 M⊙). These strong radiation fields lead to the destruction of the gas component in protoplanetary discs within 1 Myr, implying that gas giant planets must either form extremely rapidly (<1 Myr), or that they exclusively form in star-forming regions like Taurus, which contain no intermediate-mass or massive stars. The latter scenario is in direct tension with meteoritic evidence from the Solar system that suggests the Sun and its protoplanetary disc was born in close proximity to massive stars.

Constraints on star formation in NGC 2264

“…Alves et al 2020;Segura-Cox et al 2020), they are likely to have their orbits affected at densities in the range 100 − 1000 M ⊙ pc −3 (Adams et al 2006;Parker & Quanz 2012). At the lower end of the scale, regions with densities < 100 M ⊙ pc −3 could still affect planet formation if massive stars are present due to Far Ultra Violet (FUV) radiation from stars more massive than 10 M ⊙ , which can lead to photoevaporation of protoplanetary discs (Scally & Clarke 2002;Adams et al 2004;Concha-Ramírez et al 2019;Nicholson et al 2019;Parker et al 2021). Given that S Mon and IRS 1 are both more massive than 10 M ⊙ (e.g.…”

Constraints on star formation in NGC2264

“…Alves et al 2020;Segura-Cox et al 2020), they are likely to have their orbits affected at densities in the range 100 − 1000 M ⊙ pc −3 (Adams et al 2006;Parker & Quanz 2012). At the lower end of the scale, regions with densities < 100 M ⊙ pc −3 could still affect planet formation if massive stars are present due to Far Ultra Violet (FUV) radiation from stars more massive than 10 M ⊙ , which can lead to photoevaporation of protoplanetary discs (Scally & Clarke 2002;Adams et al 2004;Concha-Ramírez et al 2019;Nicholson et al 2019;Parker et al 2021). Given that S Mon and IRS 1 are both more massive than 10 M ⊙ (e.g.…”

The evolution of protoplanetary disc radii and disc masses in star-forming regions

“…In previous work (Parker et al 2021a), we have shown that the stellar density is the main factor in determining how many discs are destroyed by external photoevaporation. In some of those models we also included a prescription for viscous spreading, and the net effect of this viscous evolution was to accelerate the mass lost from the disc due to photoevaporation.…”

“…EUV and FUV radiation readily evaporates the gas component of protoplanetary discs (e.g. Johnstone et al 1998;Störzer & Hollenbach 1999;Hollenbach et al 2000;Scally & Clarke 2001;Adams et al 2004;Fatuzzo & Adams 2008;Nicholson et al 2019;Winter et al 2018b;Parker et al 2021a, and many others), and to a lesser extent the dust (Haworth et al 2018).…”