Stellar orbit evolution in close circumstellar disc encounters

Abstract

The formation and early evolution of circumstellar discs often occurs within dense, newborn stellar clusters. For the first time, we apply the moving-mesh code AREPO, to circumstellar discs in 3-D, focusing on disc-disc interactions that result from stellar fly-bys. Although a small fraction of stars are expected to undergo close approaches, the outcomes of the most violent encounters might leave an imprint on the discs and host stars that will influence both their orbits and their ability to form planets. We first construct well-behaved 3-D models of self-gravitating discs, and then create a suite of numerical experiments of parabolic encounters, exploring the effects of pericenter separation r p , disc orientation and disc-star mass ratio (M d /M * ) on the orbital evolution of the host stars. Close encounters (2r p disc radius) can truncate discs on very short time scales. If discs are massive, close encounters facilitate enough orbital angular momentum extraction to induce stellar capture. We find that for realistic primordial disc masses M d 0.1M * , non-colliding encounters induce minor orbital changes, which is consistent with analytic calculations of encounters in the linear regime. The same disc masses produce entirely different results for grazing/colliding encounters. In the latter case, rapidly cooling discs lose orbital energy by radiating away the energy excess of the shock-heated gas, thus causing capture of the host stars into a bound orbit. In rare cases, a tight binary with a circumbinary disc forms as a result of this encounter.

Protoplanetary disc truncation mechanisms in stellar clusters: comparing external photoevaporation and tidal encounters

“…Lada & Lada 2003). If this environment is sufficiently dense, a protoplanetary disc (PPD) can undergo truncation and mass loss due to close encounters (Clarke & Pringle 1993;Ostriker 1994;Hall et al 1996;Pfalzner et al 2005;Olczak et al 2006;Breslau et al 2014;Muñoz et al 2015;Winter et al 2018) and external photoevaporation (Störzer & Hollenbach 1999;Armitage 2000;Scally & Clarke 2001;Adams 2010;Facchini et al 2016;Guarcello et al 2016). The physical importance of these within a cluster, a physical property that has only recently become measurable.…”

Accretion disks in luminous young stellar objects

“…Indeed, the ionizing stellar radiation of the Herbig Be stars could photoevaporate the disk rapidly (Hollenbach et al, 2000). An alternative explanation involves tidal interactions in a crowded birth environment leading to disk truncation (Muñoz et al, 2015). The fact that the disks of embedded YSOs display an opposite trend to that seen among the HAeBe stars could therefore mean that photo-evaporation is not strong enough to significantly affect the disk (or toroids) on a timescale of a few 10 5 yr, the typical formation timescale for high-mass stars (McKee & Tan, 2002).…”

Gravitational Instabilities in Circumstellar Disks

“…This constraint is also equivalent to the constraint on disk mass presented in Equation (2) in Section 2. In the general case where both contributions (of the central star and of the disk) are important, there is no analytical solution to the hydrostatic balance equation, but a simple and accurate interpolation formula between the two results above has been found by Bertin & Lodato (1999) (see also Lodato 2007;Muñoz et al 2015):…”