Comparison of the critical metal mass expressions of Brouwers & Ormel (2020) (isothermal, gray) and this work (non-isothermal, black), both examined with different opacities. The dotted lines indicate grain-free envelopes, whereas the solid lines assume the accretion of small pebbles that can grow, fragment and erode according to our model. The dash-dotted line corresponds to the accretion of 100 μm pebbles thatare kept at a constant size during their sedimentation.