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Open research questions in Astrophysics and Star Formation Studies

54 unresolved questions extracted from the limitations and future-work sections of 345 Astrophysics and Star Formation Studies papers in our library. Each links back to the study that raised it.

What the literature leaves open

  • Despite this quantitative difference, both methods consistently con- clude that the turbulent heating rate is insufficient to offset the radiative cooling rate within the cluster core (r < 50 kpc), although they become more comparable at larger radii.

    Simulating AGN Feedback in Galaxy Clusters with Pre-existing Turbulence · 2026 · DOI

  • We appear to be missing ∼80% of nearby old PNe and GPNe in this age range, which remain to be discovered, are effectively invisible because they have faded and are not interacting strongly with the ISM, or have already been stripped by an interaction with dense ISM.

    SDSO 1 is a Shocked Ghost Planetary Nebula in Front of M 31 · 2026 · DOI

  • Despite the growing number of compact active galactic nuclei (AGN) at $z>4$ discovered by JWST, their formation and evolution remain poorly understood.

    BlackTHUNDER Reveals a Massive Filament around a Compact AGN at $z\simeq5.23$ · 2026

  • Circumbinary disks are commonly observed around post-asymptotic giant branch (post-AGB) star binaries, yet their formation and especially their long-term evolution remain unclear.

    Circumbinary disk formation through AGB star winds · 2026

  • In this work, we have studied the prestellar core L1506C in the Taurus molecular cloud. We made use of the Herschel FIR and NIKA2 millimeter observations analyzed with a 3D radiative transfer modeling with SOC that included both diffuse ISM type dust and evolved grains from the recent THEMIS 2 dust model. We combined the Herschel and NIKA2 data with a selfdeveloped approach using the software scanam_nika. For the first time, we performed MBB modeling and 3D modeling of the source over the whole spectral range, from 160 µm to 2 mm. We also used an NIR extinction map observed with WIRCam and scattering observed with Spitzer to constrain the models. The main results are the following: – L1506C is fragmented into two cores, and the MBB modeling revealed their similar properties: a color temperature of T ≈ 11 K, β ≈ 1.9, NH2 ≈ 2.5 × 1021 cm−2, and a mass of 0.3 M(cid:12), which is smaller than their Jeans mass. – Both T and β within the MBB modeling area show anticorrelated spatial variations beyond uncertainty levels: T decreases from 14.5 K in the envelope surrounding the cores to ∼ 11 K in the cores, and β increases from 1.46 in the envelope to ∼ 1.9 in the cores. The anticorrelation has a slope of −0.06, which was revealed by the hierarchical Bayesian method. – The dust emissivity index in NIKA2 wavelength bands (βmm), calculated with the reconstructed NIKA2 maps, has a mean value of 1.88 ± 0.27 within the MBB modeling area with 2 mm weight > 8000. The value is equal to 2.15 ± 0.39 if one uses the original NIKA2 maps and agrees with other prestellar core values found in the literature. – With 3D radiative transfer modeling, we were able to reproduce the observed millimeter emission with a residual of (cid:46) 10% for the cores and coreshine within 1σ. Extinction is still overestimated by a factor ∼ 2.8. The cloud geometry is degenerate and cannot be well constrained with only dust emission or NIR extinction data. – Radiative transfer modeling revealed in 3D a central dust temperature as low as 8 K, which is about 3 K lower than derived from MBB modeling. The model NH2 has a maximum value of 1.3 × 1022 cm−2, about 1.7 times higher than the one derived from MBB modeling, indicating the importance of radiative transfer modeling for correctly constraining NH2. – The modeling of the radiative transfer shows that porous icecoated grains with a size of up to 0.7 µm, which is larger than those found in the diffuse interstellar medium, are necessary to adjust the FIR-millimeter emission and to reproduce the Article number, page 14 of 21 coreshine effect while having a cloud volume density compatible with measurements from independent observations of molecular lines. – The grain evolution from diffuse type to evolved grains occurs at densities (nH) between 1500 and 4500 cm−3. For a threshold density of n0 =3000 H/cm3, the amount of evolved grains reaches 50% at AV ≈ 4.

    Tracing grain growth in the forming prestellar core L1506C with 3D modeling of Herschel , IRAM, and CFHT observations · 2026 · DOI

  • To date only one chiral species, propylene oxide, has been observed in the interstellar medium but little is known about the chemistry that leads to a detectable abundance of this molecule in Sagittarius B2.

    Charge transfer from ammonia neutralizes propylene oxide cations: Implications for the astrochemistry of chiral molecules · 2026

  • The CO emission does not show clear signatures of outflow emission (through morphology and/or velocty structure) and it is primarily associated with the elongated structure, while the disk kinematics and orientation remain uncertain. However, the nature of the structure and the extent to which this material is effectively accreting onto the disk remain uncertain.

    The environmental imprint on molecular layering in the dusty streamer of M512 · 2026 · DOI

  • HST remains uniquely positioned to address key open questions in the field, such as resolving the vertical atmospheric structure, long term evolution of the atmosphere, and detection of UV aurora in the upper atmosphere, primarily in conjunction with other facilities that probe wavelength regimes that cannot be reached with instruments on HST.

    Building a Roadmap for Hubble Science into the 2030s: Revealing Atmospheric Structure and Evolution in Substellar Worlds Using HST · 2026

  • However, the phenomena through which we observe AGN are multiphase and multiscale, which can lead to conflicting results for how significantly and to what extent AGN influence the ISM.

    Surveying the Whirlpool at Arcseconds with NOEMA (SWAN) · 2026 · DOI

  • However, more robust EMRI trajectory models yield no reliable solution, possibly due to narrow likelihood peaks in a high-dimensional space with sparse data.

    Even a Precessing Clock Is Right Twice per Orbit—The Superperiods of eRO-QPE2 and Challenges for Quasiperiodic Eruption Orbital Models · 2026 · DOI

  • (2010) revisited this crite- rion, as it does not account for the variation in AGN contribution to the continuum emission, and the authors proposed the ratio /LPAH7.

    MICONIC: The multiphase circumnuclear region of Centaurus A as seen with JWST/MIRI MRS observations. I. Spectral inventory and properties of the warm molecular disk · 2026 · DOI

  • This means that their estimates include dense material from the OMC, which may not be representative of the front shell revealed by the Hi emission at vLSR < 1 km s−1.

    The Neutral Atomic Hydrogen in the solar neighborhood (NeAtHood) project I. Ghost in the shell: Neutral atomic hydrogen in the extended Orion nebula · 2026 · DOI

  • A. Strengths of the Proposed Framework i. Reproducibility and Open Science The entire pipeline is built on publicly available data and open-source software. All analysis scripts and derived data products will be archived with a DOI (e.g., on Zenodo), ensuring complete transparency and reproducibility. – ii. Genuine Multi-Physics Integration The framework inherently bridges scales—from galactic dynamics to cloud collapse—and physical processes (gravity, MHD, radiative cooling, feedback) in a self-consistent manner. - **Efficient Use of Resources**: It maximizes the scientific return on significant public investments (JWST, ALMA, Chandra) by creating a new, integrative analysis pathway for archival data. - **Guidance for Future Observations**: Predictions from the calibrated resistive MHD model can identify specific, testable hypotheses and optimal targets for future observing cycles with JWST, ALMA, or next-generation facilities. B. Methodological Limitations and Considerations i.

    Multiscale Modelling of Galaxy Collisions with Integrated Resistive MHD and Stellar Feedback · 2026 · DOI

  • The foreground dust screen and internal dust models from Calzetti et al. (1994) are compared to simulation results in Figure 8, but the clumpy dust distribution at small scales (with regions of high and low dust within the same sightline) may not conform to either model. The paper does not develop or test alternative dust geometries that account for the observed clumpiness and its effect on Balmer decrement accuracy.

    Identifying Signatures of Inflow onto Face-on Galaxies Using the Balmer Decrement · 2026 · DOI

  • The analysis is restricted to a single face-on galaxy simulation at the earliest timestep. The generalizability of the Balmer decrement signatures to different galaxy masses, morphologies, inclinations, and evolutionary stages remains unexamined, limiting the applicability of the inflow detection method to broader observational samples.

    Identifying Signatures of Inflow onto Face-on Galaxies Using the Balmer Decrement · 2026 · DOI

  • The dust-to-gas ratios for inflow (~0.7%) and outflow (~0.8%) are both quite low and show only marginal differences. The paper does not explore how variations in dust-to-gas ratio across different galactic environments (varying metallicity, star formation history) would affect the reliability of using Balmer decrement to distinguish inflow from outflow components.

    Identifying Signatures of Inflow onto Face-on Galaxies Using the Balmer Decrement · 2026 · DOI

  • The comparison of extinction predictions between the simulation and observational studies is limited to quasars, Seyfert galaxies, and ULIRGs from prior work. The authors explicitly note that this comparison is underexplored for Milky Way-like galaxies which more closely resemble their simulated galaxy, requiring observational spectroscopy of local face-on galaxies to validate whether the ~0.3 magnitude AV differences predicted are detectable.

    Identifying Signatures of Inflow onto Face-on Galaxies Using the Balmer Decrement · 2026 · DOI

  • The Balmer decrement method shows only 54% accuracy for identifying in-front components with small offsets and 67% accuracy with ΔHα/Hβ > 0.3, with notably lower performance for blue-shifted components. The paper does not investigate whether combining Balmer decrement analysis with additional spectroscopic diagnostics (such as forbidden line ratios or kinematics) could improve the discrimination between inflow and outflow in face-on galaxies.

    Identifying Signatures of Inflow onto Face-on Galaxies Using the Balmer Decrement · 2026 · DOI

  • The particle-based simulation approximates particles as point sources positioned at their centers despite particles having varying sizes often larger than the 20 pc x-y scale displayed in Figure 10. This simplification may smooth the emission and dust surface density distributions; the impact of explicitly modeling particle sizes on Balmer decrement measurements and the detectability of inflow signatures requires quantification.

    Identifying Signatures of Inflow onto Face-on Galaxies Using the Balmer Decrement · 2026 · DOI

  • The work focuses on systems with Reynolds numbers comparable to the paper's simulations (see Table 1), but the applicability of findings to the full range of Reynolds numbers encountered in galaxy clusters, galactic winds, and cold stream accretion (spanning many orders of magnitude) has not been systematically explored.

    The (limited) effect of viscosity in multiphase turbulent mixing · 2026 · DOI

  • The paper demonstrates that viscosity does not significantly alter mass transfer rates between phases in the fast cooling regime (Da > 1), but the mechanism by which temperature-dependent viscosity affects the steady-state amount of gas at different temperatures remains incomplete and requires explicit investigation of thermal structure evolution.

    The (limited) effect of viscosity in multiphase turbulent mixing · 2026 · DOI

  • The study examines idealized setups with simplified initial conditions and geometry to isolate viscosity and cooling effects. Extension to more realistic multiphase configurations with asymmetric density ratios, magnetic fields, and non-uniform cooling rates in turbulent mixing layers is needed to validate findings in complex astrophysical environments.

    The (limited) effect of viscosity in multiphase turbulent mixing · 2026 · DOI

  • The interaction between viscosity and cooling in astrophysical scenarios (ICM, ISM, CGM, galactic winds, coronal rain) has not been systematically characterized across the range of Reynolds numbers comparable to those used in this study. Specifically, how viscosity affects cooling efficiency and star formation rates in ram-pressure-stripped galactic tails requires dedicated investigation.

    The (limited) effect of viscosity in multiphase turbulent mixing · 2026 · DOI

  • Current multiphase subgrid models for cosmological simulations do not account for the combined effects of radiative cooling and temperature-dependent viscosity. The paper uses constant viscosity for simplicity, but real Spitzer viscosity depends on temperature, which could affect both momentum transfer in the mixing layer and the mass inflow rate due to cooling across different temperature regimes.

    The (limited) effect of viscosity in multiphase turbulent mixing · 2026 · DOI

  • The system experienced a rising MIR and ∆V = 1 mag bump in 2014, probably indicating a missed outburst or regular variability, but the nature of this event and its relation to the 2019 and 2024 outbursts remains unclear.

    Gaia24ccy: An Outburst Followed the Footsteps of its Predecessor · 2026 · DOI

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54 open questions have been extracted from the limitations and future-work passages of 345 Astrophysics and Star Formation Studies papers in our library. Each one below links back to the study that raised it, so you can read the original claim in context.

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