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Open research questions in Astrophysical Phenomena and Observations

211 unresolved questions extracted from the limitations and future-work sections of 527 Astrophysical Phenomena and Observations papers in our library. Each links back to the study that raised it.

What the literature leaves open

  • Confronting the theoretical frequency relations with observed HF-QPO data, - Examining how the pair (M, p) can be constrained from timing measurements

    Circular-orbit dynamics and QPO constraints in static Einstein–scalar–Gauss–Bonnet black holes · 2026 · DOI

  • The paper identifies technical challenges in simulating near-Eddington accretion, including the need for high-resolution meshes. It also notes the challenge of modeling radiation transport and its effects on accretion. The study highlights the difficulty of capturing the complex interplay between magnetic field topology, black hole spin, and radiation transport.

    Radiation GRMHD Models of Accretion onto Stellar-mass Black Holes. III. Near-Eddington Accretion · 2026 · DOI

  • The paper identifies a gap in understanding the effects of magnetic field topology and black hole spin on near-Eddington accretion. It also highlights the need for a comprehensive analysis of radiation transport in these systems. The study notes that prior work has focused on super-Eddington flows, leaving a gap in understanding near-Eddington accretion.

    Radiation GRMHD Models of Accretion onto Stellar-mass Black Holes. III. Near-Eddington Accretion · 2026 · DOI

  • The paper identifies the challenge of understanding the origin of rapid fluctuations in the tails of long X-ray bursts. The paper also identifies the challenge of modeling the spectral properties of X-ray bursts, including the need to account for ionized reflection and other complex phenomena. The paper notes the challenge of working with limited data, including the need to ignore data below 0.7 keV due to instrumental limitations.

    Do Accretion Disks Get Bent Out of Shape? Investigating the Origin of Rapid Fluctuations in the Tails of Long Thermonuclear X-Ray Bursts · 2026 · DOI

  • small sample size of 5 bursts with fluctuations and 5 bursts without fluctuations, - analysis limited to Swift bursts, - data below 0.7 keV are ignored for all fits

    Do Accretion Disks Get Bent Out of Shape? Investigating the Origin of Rapid Fluctuations in the Tails of Long Thermonuclear X-Ray Bursts · 2026 · DOI

  • The sample size of QPE host galaxies is limited to 10. The study relies on a control sample of 100 non-QPE host galaxies. The study does not account for potential dust obscuration in QPE host galaxies.

    The Delay Time Distribution of Quasiperiodic Eruptions · 2026 · DOI

  • Investigate the relationship between QPEs and extreme mass ratio inspirals (EMRIs). Study the effect of dust obscuration on the observed properties of QPE host galaxies. Expand the sample size of QPE host galaxies to improve statistical significance.

    The Delay Time Distribution of Quasiperiodic Eruptions · 2026 · DOI

  • a full N-body simulation of the subsequent evolution over 495 Myr is infeasible, - the internal two-body relaxation between young disk stars is quite different from that of old NSC stars, - the simulation is limited to a specific scenario where HVSs are slingshot by the SMBH-IMBH binary

    A Model for the Enhanced Production Rate of Early-type Hypervelocity Stars in the Galactic Halo · 2026 · DOI

  • further study of the star formation region of the NSC, - investigation of the gravitational torque from the nonspherical GC potential, - exploration of different close interactions like the HVS ejections in the Hills mechanism

    A Model for the Enhanced Production Rate of Early-type Hypervelocity Stars in the Galactic Halo · 2026 · DOI

  • the study is based on a simplified model, - the model does not consider background models and more complex spot geometries, - the study requires further systematic study, - the results are based on synthetic pulse-profiles

    An Intrinsic Degeneracy in a Simplified Semianalytic Two-spot Model for Thermal X-Ray Pulse Profiles · 2026 · DOI

  • further systematic study on the effect of the degeneracy in real observational posteriors, - study on the distinction of the two modes in real observation with background models, - analysis of NICER data and synthetic data

    An Intrinsic Degeneracy in a Simplified Semianalytic Two-spot Model for Thermal X-Ray Pulse Profiles · 2026 · DOI

  • However, its impact on the surrounding accretion disk remains insufficiently explored.

    Magnetic Reconnection Heating of Thin Accretion Disks around Kerr Black Holes · 2026

  • Whether a rotating black hole (BH) immersed in an external magnetic field charges up to the Wald value $Q_{\rm W}=2aMB$, where $M$ and $a$ are the BH mass and spin parameter, and $B$ is the strength of the external field, is a long-standing open question in BH electrodynamics, with consequences for charge separation, particle acceleration and the structure of BH magnetospheres.

    Charging of rotating black holes: kinetic simulations of black hole magnetospheres · 2026

  • However, no robust LRD candidates have been identified at z > 10, because commonly used NIRCam photometry covers wavelengths up to ∼5 μ m and is insufficient to capture the characteristic V-shaped spectral energy distributions (SEDs) of LRDs.

    Discovery of a Little Red Dot Candidate at z ≳ 10 in COSMOS-web Based on MIRI-NIRCam Selection · 2025 · DOI

  • Abstract In certain scenarios, the accreted angular momentum of plasma onto a black hole could be low; however, how the accretion dynamics depend on the angular momentum content of the plasma is still not fully understood.

    The Impact of Plasma Angular Momentum on Magnetically Arrested Flows and Relativistic Jets in Hot Accretion Flows around Black Holes · 2025 · DOI

  • Yet, the relative importance of turbulent and wind-driven angular momentum transport is still poorly understood.

    Winds and Disk Turbulence Exert Equal Torques on Thick Magnetically Arrested Disks · 2024 · DOI

  • A dedicated broadband, time-resolved study of the evolution of the continuum properties is needed. Further analysis of the XMM-Newton data and other observations of NGC 5204 X-1 is required.

    Unveiling the biconical geometry of the outflow in the ultraluminous X-ray source NGC 5204 X-1 · 2026 · DOI

  • The viewing angle differences between NGC 5204 X-1 and SS433 complicate direct comparative analysis of their outflow properties and require systematic investigation across different inclination angles.

    Unveiling the biconical geometry of the outflow in the ultraluminous X-ray source NGC 5204 X-1 · 2026 · DOI

  • Prior work has focused on the eikonal regime for deriving analytic formulas for quasinormal mode frequencies. There is a need for a more general expansion beyond the eikonal regime.

    Analytic Expressions for Quasinormal Modes of a Regular Black Hole Sourced by a Dehnen-Type Halo · 2026 · DOI

  • While comparison with numerical WKB results validates the analytic approach, experimental or observational validation of the quasinormal mode predictions remains absent.

    Analytic Expressions for Quasinormal Modes of a Regular Black Hole Sourced by a Dehnen-Type Halo · 2026 · DOI

  • The study is limited to the effective field theory extension of general relativity. The adiabatic approximation is adopted, which may not be valid for all systems.

    Gravitational radiations from periodic orbits around a black hole in the effective field theory extension of general relativity · 2026 · DOI

  • Further study is needed to understand the implications of the paper's findings for gravitational wave astronomy. The development of future space-based gravitational wave missions could be informed by the paper's results. The study of periodic orbits in EFTGR could be extended to other astrophysical contexts.

    Gravitational radiations from periodic orbits around a black hole in the effective field theory extension of general relativity · 2026 · DOI

  • Further study of SDSS J1532 and other triple black hole candidates is needed to confirm their nature and properties. The development of new methods and techniques for detecting and analyzing dual AGNs and BBHs is necessary. The study of the evolution of galaxies and the role of black holes in shaping galaxy evolution should continue.

    SDSS J153231.80+420342.7: A triple black hole candidate with a close binary black hole · 2026 · DOI

  • The scenario of variations in the intrinsic accretion rates cannot explain the properties of broad Balmer emission lines in SDSS J1011+5442.

    Clues for the accretion-regulated dust torus in the changing-look active galactic nucleus SDSS J101152.98+544206.4 · 2026 · DOI

  • The GDS is a numerical model and may not capture all the complexities of the real universe. The simulations are limited to a specific range of parameters and may not be applicable to all scenarios.

    Multiverse, Black Hole Mechanism and Finite Core - GDS (Gravitational Dynamic System) · 2026 · DOI

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211 open questions have been extracted from the limitations and future-work passages of 527 Astrophysical Phenomena and Observations 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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