pith. sign in

arxiv: 2506.04415 · v1 · submitted 2025-06-04 · 🌌 astro-ph.EP

Modelling shadows in scattered light observations as signals from companions in protoplanetary discs

Deniz Akansoy , Helen C. Petrou , Giulia Ballabio , Anna B.T. Penzlin This is my paper

Pith reviewed 2026-05-19 10:29 UTC · model grok-4.3

classification 🌌 astro-ph.EP
keywords protoplanetary discsscattered light observationsembedded companionsshadowsradiative transferplanet detectiondisc thermal structure
0
0 comments X

The pith

Companions of 14 Jupiter masses or larger in protoplanetary discs cast detectable shadows whose width and depth depend on their mass and orbital distance.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper uses radiative transfer simulations to model how planets or brown dwarfs embedded in protoplanetary discs affect the light scattered from the disc's surface. It finds that only companions at least 14 times the mass of Jupiter produce clear radial shadows across a range of distances from 5 to 30 astronomical units. The authors then create a simple formula that predicts the shadow's width and depth from the companion's mass and location. A sympathetic reader would care because these shadows are already seen in telescope images, and this work suggests they can be used to find and weigh hidden companions that are otherwise difficult to detect directly. The simulations also show that the shadows cool the disc, which could change how chemistry and planet formation proceed inside it.

Core claim

Using 3D radiative transfer simulations with RADMC-3D, companions with masses equal to or greater than 14 Jupiter masses consistently cast detectable shadows throughout the disc. An empirical solution is derived to describe the width and depth of the shadow as functions of companion mass and location. These shadows also influence the disc thermal structure with notable cooling effects.

What carries the argument

3D radiative transfer simulations modeling the shadowing effects of embedded companions on 0.1 μm dust grains well-coupled to the gas in protoplanetary discs.

If this is right

  • Shadow features observed in scattered light images could serve as reliable indicators of companion mass and position.
  • Companion shadows influence the disc thermal structure with cooling effects that could impact disc chemistry and the dynamics of planet formation.
  • Companions below 14 Jupiter masses do not consistently produce detectable shadows.
  • This provides an indirect method for identifying and characterising otherwise challenging-to-detect objects within these discs.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Existing SPHERE images of protoplanetary discs could be re-examined with the empirical formula to estimate masses and orbits of unseen companions.
  • Multi-epoch observations might check whether shadow locations move in step with predicted companion orbits.
  • The reported cooling could shift snow lines or chemical signatures in ways measurable at submillimeter wavelengths.
  • The same modeling approach could be extended to discs at earlier stages of evolution to test when massive companions first appear.

Load-bearing premise

Dust grains of 0.1 micrometers stay well mixed with the gas, and no other disc structures or effects create similar radial shadows.

What would settle it

A clear radial shadow observed in scattered light of a protoplanetary disc confirmed by other methods to contain no companion of 14 Jupiter masses or greater, or the absence of shadows around a confirmed companion above that mass threshold.

read the original abstract

Over the past decade, SPHERE scattered light observations of protoplanetary discs have revealed previously unseen features with unprecedented resolution. One such feature are radial streaks of reduced brightness that are commonly interpreted as shadows. A possible cause for these shadows is an embedded companion within the disc. In this work, we use 3D radiative transfer simulations with RADMC-3D to investigate the shadowing effects of embedded companions across a range of orbital distances (5-30 au) and companion masses (0.5-30 Jupiter masses). We model 0.1 $\mu$m dust grains, which are well-coupled to the gas, to produce synthetic scattered light images of the disc. Companions with masses equal to or greater than 14 Jupiter masses consistently cast detectable shadows throughout the disc. We hence derive an empirical solution to describe the width and depth of the shadow as functions of companion mass and location. This scaling suggests that shadow features observed in scattered light images could serve as reliable indicators of companion mass and position, providing an indirect method for identifying and characterising otherwise challenging-to-detect objects within these discs. Additionally, our analysis reveals that companion shadows influence the disc thermal structure, with notable cooling effects that could impact disc chemistry and the dynamics of planet formation.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 3 minor

Summary. The paper claims that through 3D radiative transfer simulations of protoplanetary discs with embedded companions using RADMC-3D, companions with masses of 14 Jupiter masses or greater produce consistently detectable shadows in scattered light. An empirical solution is derived for the shadow's width and depth depending on companion mass and orbital location, suggesting shadows as indicators for companion properties. The work also notes cooling effects on the disc's thermal structure.

Significance. Should the findings prove robust, they offer a promising indirect technique for identifying and characterizing embedded companions in protoplanetary discs via their shadow signatures in high-resolution scattered light imaging. The application of established radiative transfer methods lends credibility to the modeling approach, and the provision of an empirical scaling relation represents a practical output for observers.

major comments (2)
  1. [Simulation Setup] The background disc parameters, including scale height, surface density profile, and flaring, are not varied in the simulations. This renders the reported 14 M_Jup detectability threshold and the empirical fit for shadow properties specific to the chosen disc model. Shadow visibility in scattered light is sensitive to the disc's vertical optical depth and geometry, so exploring variations in these parameters is required to substantiate the generality of the results.
  2. [Results and Discussion] The paper assumes that 0.1 μm dust grains are well-coupled to the gas and that other potential sources of radial shadows (e.g., disc warps or inner disc misalignments) do not produce comparable features. Without additional tests or comparisons, this assumption underpins the interpretation but lacks explicit validation against alternatives.
minor comments (3)
  1. [Abstract] The mention of 'notable cooling effects' should include a reference to the specific section or figure where these effects are quantified and discussed.
  2. [Methods] Provide more details on the criteria used to determine shadow 'detectability' in the synthetic images, such as the minimum contrast ratio or signal-to-noise threshold applied.
  3. [Figures] Include error bars or uncertainty estimates on the empirical fit parameters if derived from multiple simulations.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their thoughtful and constructive comments on our manuscript. Below we address each major comment in turn, indicating the revisions we intend to make.

read point-by-point responses

  1. Referee: [Simulation Setup] The background disc parameters, including scale height, surface density profile, and flaring, are not varied in the simulations. This renders the reported 14 M_Jup detectability threshold and the empirical fit for shadow properties specific to the chosen disc model. Shadow visibility in scattered light is sensitive to the disc's vertical optical depth and geometry, so exploring variations in these parameters is required to substantiate the generality of the results.

    Authors: We agree that the reported 14 M_Jup threshold and the empirical scaling relations are specific to the fixed disc parameters adopted in our simulations. These parameters were chosen to be representative of typical protoplanetary discs observed in scattered light. A full exploration of variations in scale height, surface density, and flaring would indeed provide greater generality but would require a substantially larger suite of 3D radiative transfer calculations. In the revised manuscript we will add a new subsection in the discussion that explicitly states the adopted disc model, acknowledges the specificity of the threshold, and offers qualitative guidance on how changes in vertical optical depth or geometry would be expected to shift the mass threshold and shadow properties. This addition will help readers assess the applicability of our results to other discs. revision: partial

  2. Referee: [Results and Discussion] The paper assumes that 0.1 μm dust grains are well-coupled to the gas and that other potential sources of radial shadows (e.g., disc warps or inner disc misalignments) do not produce comparable features. Without additional tests or comparisons, this assumption underpins the interpretation but lacks explicit validation against alternatives.

    Authors: The choice of 0.1 μm grains follows the standard assumption that such small particles remain well-coupled to the gas in the disc regions probed by scattered light; this is consistent with dust dynamics calculations and is widely used in the literature for modeling SPHERE-like observations. Our study does not claim that companions are the sole origin of radial shadows, but rather demonstrates that companions above a certain mass produce detectable shadows with characteristic properties. To address the referee’s concern, we will expand the discussion to include a concise comparison of the expected morphology and radial dependence of companion-induced shadows versus those produced by warps or misalignments, citing relevant prior work. This will clarify the distinguishing observational signatures without requiring new simulations. revision: partial

Circularity Check

0 steps flagged

No circularity: empirical fit follows from independent radiative-transfer simulations

full rationale

The central results rest on RADMC-3D 3D radiative-transfer runs that vary only companion mass (0.5–30 Mjup) and semi-major axis (5–30 au) while the background disc structure, scale height, surface density, and 0.1 μm dust properties remain fixed. The reported 14 Mjup detectability threshold and the empirical functions for shadow width and depth are obtained by post-processing the synthetic scattered-light images and fitting the measured shadow properties; this is a data-driven summary of simulation outputs, not a self-definitional reduction or a fitted input relabeled as a prediction. No load-bearing self-citations, uniqueness theorems, or smuggled ansatzes appear in the derivation chain. The physical modeling therefore supplies independent content.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The central result rests on a standard radiative-transfer code, a fixed dust size chosen for coupling, and an empirical fit derived from the simulation outputs rather than new physical postulates.

free parameters (1)
  • 14 Jupiter-mass detectability threshold
    Minimum mass at which shadows become consistently detectable is read off from the simulation grid.
axioms (1)
  • domain assumption 0.1 μm dust grains are well-coupled to the gas.
    Explicit modeling choice stated for producing the synthetic scattered-light images.

pith-pipeline@v0.9.0 · 5767 in / 1251 out tokens · 55691 ms · 2026-05-19T10:29:11.842205+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

What do these tags mean?
matches
The paper's claim is directly supported by a theorem in the formal canon.
supports
The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends
The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses
The paper appears to rely on the theorem as machinery.
contradicts
The paper's claim conflicts with a theorem or certificate in the canon.
unclear
Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.