Protoplanetary disks, the birthplace of planets, are expected to be gravitationally unstable in their early phase of evolution. IM Lup, a well-known T-Tauri star, is surrounded by a protoplanetary disk with spiral arms. The disk was probably caused by gravitational instability. The IM Lup disk has been observed using various methods, but developing a unified explanatory model is challenging. Here we present a physical model of the IM Lup disk that offers a comprehensive explanation for diverse observations spanning from near-infrared to millimetre wavelengths. Our findings underscore the importance of dust fragility in retaining the observed millimetre emission and reveal the preference for moderately porous dust to explain the observed millimetre polarization. We also find that the inner disk region is probably heated by gas accretion, which provides a natural explanation for bright millimetre emission within 20 au. The actively heated inner region in the model casts a 100 au-scale shadow that aligns seamlessly with the observation of near-infrared scattered light. The accretion heating also supports the fragile-dust scenario in which accretion efficiently heats the disk midplane. Due to the fragility of the dust, it is unlikely that a potential embedded planet at 100 au formed through pebble accretion in the smooth disk, which suggests that local dust enhancement boosted pebble accretion or that there are alternative pathways, such as outward migration or gravitational fragmentation.

原行星盘是行星的诞生地，预计在其演化的早期阶段在引力上不稳定。 IM Lup 是一颗著名的金牛座 T 型恒星，周围环绕着带有旋臂的原行星盘。该圆盘可能是由重力不稳定造成的。 IM Lup 盘已使用各种方法进行观察，但开发统一的解释模型具有挑战性。在这里，我们提出了 IM Lup 圆盘的物理模型，该模型为从近红外到毫米波长的各种观测提供了全面的解释。我们的研究结果强调了灰尘脆性在保留观察到的毫米发射方面的重要性，并揭示了对中等孔隙灰尘的偏好来解释观察到的毫米偏振。我们还发现盘内区域可能被气体吸积加热，这为 20 天以内的明亮毫米发射提供了自然的解释。模型中主动加热的内部区域投射出 100 au 尺度的阴影，与近红外散射光的观察结果无缝吻合。吸积加热还支持易碎灰尘场景，其中吸积有效地加热磁盘中板。由于尘埃的脆弱性，100 au的潜在嵌入行星不太可能通过光滑圆盘中的卵石吸积形成，这表明局部尘埃增强促进了卵石吸积，或者存在其他途径，例如向外迁移或重力碎片化。