Radiative feedback from protoplanets in self-gravitating protoplanetary discs

Abstract

It is well known that massive protoplanetary discs are gravitationally unstable beyond tens of au from their parent stars. The eventual fate of the self-gravitating gas clumps born in the disc is currently not understood, although the range of uncertainty is well known. If clumps migrate inwards rapidly, they are tidally disrupted, which may leave behind giant-or terrestrial-like planets. On the other hand, if clumps migrate less rapidly, then they tend to accrete gas, becoming proto-brown dwarfs or low-mass companions to the parent star.Herewe argue that radiative feedback of contracting clumps (protoplanets) on their discs is an important effect that has been overlooked in previous calculations.We show analytically that temperature in clump's vicinity may be high enough to support a quasi-static atmosphere if the clump mass is below a critical value, M,cr ̃ 6 Jupiter masses (MJ). This may arrest further gas accretion on to the clump and thus promote formation of planets rather than low-mass companions.We use numerical simulations to evaluate these analytical conclusions by studying migration and accretion of gas clumps as a function of their initial mass, Mi. Simulations neglecting the radiative preheating effect showthat gas clumpswith mass lessthañ2MJ migrate inwards rapidly; more massive clumps result in low-mass companions. In contrast, simulations that include radiative preheating from the clump show that clumps as massive as 8MJ migrate inwards rapidly and end up tidally disrupted in the inner disc. We conclude that, with other parameters being equal, previous simulations neglecting radiative feedback from self-gravitating clumps overestimated the population of brown dwarfs and low-mass stellar companions and underestimated the population of planets. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.