Characterising face-on accretion onto and the subsequent contraction of protoplanetary discs

Abstract

Context. Observations indicate that stars generally lose their protoplanetary discs on a timescale of about 5 Myr. Which mechanisms are responsible for the disc dissipation is still debated. Aims. Here we investigate the movement through an ambient medium as a possible cause of disc dispersal. The ram pressure exerted by the flow can truncate the disc and the accretion of material with no azimuthal angular momentum leads to further disc contraction. Methods. We derive a theoretical model from accretion disc theory that describes the evolution of the disc radius, mass, and surface density profile as a function of the density and velocity of the ambient medium. We test our model by performing hydrodynamical simulations of a protoplanetary disc embedded in a flow with different velocities and densities. Results. We find that our model gives an adequate description of the evolution of the disc radius and accretion rate onto the disc. The total disc mass in the simulations follows the theoretically expected trend, except at the lowest density where our simulated discs lose mass owing to continuous stripping. This stripping may be a numerical rather than a physical effect. Some quantitative differences exist between the model predictions and the simulations. These are at least partly caused by numerical viscous effects in the disc and depend on the resolution of the simulation. Conclusions. Our model can be used as a conservative estimate for the process of face-on accretion onto protoplanetary discs, as long as viscous processes in the disc can be neglected. The model predicts that in dense gaseous environments, discs can shrink substantially in size and can, in theory, sweep up an amount of gas of the order of their initial mass. This process could be relevant for planet formation in dense environments.

Small Protoplanetary Disks in the Orion Nebula Cluster and OMC1 with ALMA

“…Disk interactions with the interstellar medium (ISM) during the embedded phase can contribute significantly to decreasing disk sizes. Wijnen et al (2017a) model two such interactions: face-on accretion and ram pressure stripping. The former process contracts disks by adding ISM material without azimuthal angular momentum, thus shrinking the disk to conserve total angular momentum, while the latter removes material due to the pressure exerted by the surrounding gas moving at a different velocity than the disk.…”

The viscous evolution of circumstellar discs in young star clusters

“…References for the observational values can be found in Table 1. stripping and face-on accretion on disks. Wijnen et al (2016Wijnen et al ( , 2017 demonstrated that face-on accretion of ambient gas in embedded star-forming regions can cause circumstellar disks to contract, while the ram pressure exerted by the interstellar medium strips the outer parts of the disks. Nearby supernovae could also have imporant repercussions on the morphology and mass of circumstellar disks (Close & Pittard 2017;Portegies Zwart et al 2018), but since our clusters are very young we ingore this effect.…”

On the diversity and statistical properties of protostellar discs

“…The discs form from the collapse and accretion of gas from the molecular cloud, and in many cases this continues to the end of the simulation. Conversely, discs can accrete gas (Moeckel & Throop 2009;Scicluna et al 2014;Wijnen et al 2016Wijnen et al , 2017a or suffer from ram-pressure stripping as they pass through density cloud material (Wijnen et al 2016). Star-disc interactions can also strip away or truncate discs (Clarke & Pringle 1991b), and/or energy loss during a star-disc interaction can produce binaries or high-order multiple systems from protostars that were previously unbound (Clarke & Pringle 1991a;Hall, Clarke & Pringle 1996).…”