Centrally concentrated star formation in young clusters II: Jet feedback
Pith reviewed 2026-06-27 06:08 UTC · model grok-4.3
The pith
Protostellar jets lower star formation efficiency and produce cluster structures that better match observations in dense clouds.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
In centrally concentrated initial conditions, runs with jets form stellar systems that better reproduce the observed range of the projected structural parameter Q_2D in young clusters than runs without jets, indicating that protostellar jets are an important early feedback channel even in centrally concentrated clouds that regulates star formation efficiencies and shapes the emerging cluster structure.
What carries the argument
Paired Torch simulations of a 2500-solar-mass centrally concentrated cloud, with and without protostellar jets, compared through global star formation diagnostics and the structural measure Q_2D.
If this is right
- Jet feedback reduces overall star formation efficiency from 19-33 percent to 12-16 percent.
- Jets shift star formation from continuous to discrete bursts.
- Jets leave stellar populations that are less tightly bound and have higher virial parameters.
- Jets produce more extended and substructured stellar systems.
Where Pith is reading between the lines
- If jets shape structure this early, later gas expulsion may start from a less bound configuration than usually assumed.
- The bursty star formation pattern could imprint on the age spreads observed in some young clusters.
- Higher-resolution runs or different cloud masses could test whether the Q_2D improvement persists when more small-scale physics is resolved.
Load-bearing premise
The chosen centrally concentrated cloud model and the way the simulations isolate jet feedback accurately represent the conditions under which real young clusters form.
What would settle it
A survey measuring Q_2D in a sample of very young clusters still embedded in centrally concentrated gas and comparing those values to the ranges produced by the jet and no-jet runs.
Figures
read the original abstract
Protostellar jets are one of the earliest forms of stellar feedback, but their impact on star formation and cluster assembly in centrally concentrated molecular clouds remains poorly understood. We study how protostellar jets affect the star formation efficiency, the temporal variability of star formation, star cluster structure, and the early dynamical state of centrally concentrated, newly forming star clusters using the Torch star cluster formation framework. We adopt a centrally concentrated initial cloud model with mass M = 2.5 x 10^3 solar masses and compare six pairs of simulations with and without protostellar jets, supplemented by one additional higher resolution pair of simulations. We analyze our simulations using global star formation diagnostics together with structural and dynamical measures of the stellar population. Models with jet feedback achieve star formation efficiencies of 12-16%, while the corresponding models without jets yield higher efficiencies of 19-33%. Jets also cause star formation to occur in discrete bursts rather than continuously, to produce more extended and substructured stellar systems, and to leave behind stellar populations that are less tightly bound and have higher virial parameters. In our centrally concentrated initial conditions, runs with jets form stellar systems that better reproduce the observed range of the projected structural parameter Q_2D in young clusters than runs without jets, indicating that protostellar jets are an important early feedback channel even in centrally concentrated clouds that regulates star formation efficiencies and shapes the emerging cluster structure.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper uses the Torch framework to simulate star cluster formation in a single centrally concentrated molecular cloud model (M = 2.5 × 10^3 M_⊙). It compares six pairs of runs (plus one higher-resolution pair) with and without protostellar jet feedback, claiming that jets lower star formation efficiency (12–16% vs. 19–33%), produce burstier star formation, yield more extended and substructured stellar systems, and result in stellar populations whose projected structural parameter Q_2D better matches the observed range in young clusters. The authors conclude that jets constitute an important early feedback channel even in centrally concentrated clouds.
Significance. If the numerical results hold under the stated conditions, the work would provide concrete evidence that protostellar jets can regulate star-formation efficiency and imprint observable structural signatures on young clusters, offering a testable early-feedback mechanism that operates before other channels become dominant.
major comments (3)
- [Abstract / §2] Abstract and initial-conditions description: the central claim that jets are important “even in centrally concentrated clouds” rests on a single cloud mass (2.5 × 10^3 M_⊙) and concentration parameter with no additional runs at different masses, concentrations, or turbulence spectra. Without such variation the reported SFE difference and Q_2D improvement cannot be shown to be general rather than setup-specific.
- [Methods / Results] Methods and results sections: the manuscript supplies no information on spatial or mass resolution, particle or cell counts, or convergence tests for either the with-jet or without-jet runs. Because Q_2D and the structural diagnostics are sensitive to small-scale fragmentation and projection effects, the absence of these checks makes it impossible to judge whether the claimed structural differences are numerically robust.
- [Results] Results section: the SFE ranges (12–16 % vs. 19–33 %) and the statement that jets produce a “better” match to observed Q_2D are presented without uncertainties, bootstrap errors, or statistical tests on the six simulation pairs. This weakens the quantitative support for the efficiency and structural claims.
minor comments (1)
- [Abstract] The abstract states “solar masses” rather than the conventional M_⊙; consistent notation should be used throughout.
Simulated Author's Rebuttal
We thank the referee for their thoughtful comments on our manuscript. We respond to each major comment below. We will revise the manuscript to address concerns about the specificity of the model, add missing numerical details, and include more quantitative information on the results.
read point-by-point responses
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Referee: [Abstract / §2] Abstract and initial-conditions description: the central claim that jets are important “even in centrally concentrated clouds” rests on a single cloud mass (2.5 × 10^3 M_⊙) and concentration parameter with no additional runs at different masses, concentrations, or turbulence spectra. Without such variation the reported SFE difference and Q_2D improvement cannot be shown to be general rather than setup-specific.
Authors: We acknowledge that our results are based on a single cloud mass and concentration. The paper focuses on this specific centrally concentrated model to isolate the effect of jets. We will revise the abstract and section 2 to emphasize that the conclusions apply to this setup and that further studies with varied parameters are required to establish generality. revision: yes
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Referee: [Methods / Results] Methods and results sections: the manuscript supplies no information on spatial or mass resolution, particle or cell counts, or convergence tests for either the with-jet or without-jet runs. Because Q_2D and the structural diagnostics are sensitive to small-scale fragmentation and projection effects, the absence of these checks makes it impossible to judge whether the claimed structural differences are numerically robust.
Authors: We will add a dedicated paragraph in the Methods section detailing the spatial and mass resolution, the number of SPH particles or grid cells used, and the results from the higher-resolution pair of simulations. The higher-resolution runs confirm the same trends in SFE and structure, providing evidence of numerical robustness. revision: yes
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Referee: [Results] Results section: the SFE ranges (12–16 % vs. 19–33 %) and the statement that jets produce a “better” match to observed Q_2D are presented without uncertainties, bootstrap errors, or statistical tests on the six simulation pairs. This weakens the quantitative support for the efficiency and structural claims.
Authors: We will expand the Results section to list the SFE for each of the six pairs individually and report the Q_2D values for all runs. This will allow readers to assess the consistency. Given the small number of simulations, we will avoid overclaiming statistical significance but note the systematic difference across pairs. revision: partial
Circularity Check
No circularity: direct simulation comparison of jet vs. no-jet runs
full rationale
The paper reports outcomes from paired Torch simulations (with/without jets) on a fixed centrally concentrated initial cloud (M=2.5e3 Msun). Star formation efficiency (12-16% vs 19-33%), bursty SF, Q_2D distributions, virial parameters, and structural measures are direct numerical outputs, not fitted parameters renamed as predictions, not self-defined quantities, and not reduced via self-citation chains. The abstract and described methods contain no equations or steps that equate a claimed result to its own inputs by construction. The comparison is independent across the two sets of runs; the initial model is stated as an assumption but does not create circularity in the reported differences.
Axiom & Free-Parameter Ledger
free parameters (2)
- Initial cloud mass =
2.5 x 10^3 solar masses
- Number of simulation pairs =
six pairs plus one higher resolution pair
axioms (2)
- domain assumption The Torch framework correctly implements hydrodynamics, gravity, and protostellar jet feedback physics.
- domain assumption The initial cloud is centrally concentrated as modeled and representative of young cluster formation sites.
Reference graph
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discussion (0)
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