Science AI Journal
Physics and Astronomy · Research topic

Open research questions in Astrophysical Phenomena and Observations

28 unresolved questions extracted from the limitations and future-work sections of 355 Astrophysical Phenomena and Observations papers in our library. Each links back to the study that raised it.

What the literature leaves open

  • While this effect is well studied for collisionless dark matter (CDM), it remains unexplored for self-interacting dark matter (SIDM) due to the typically low DM density in SIDM halo cores.

    Echoes of self-interacting dark matter from binary black hole mergers · 2026 · DOI

  • Continued study of late-time TDE emission provides a unique opportunity to constrain the physics of disk formation and circularization, accretion disk warps, angular momentum transport, and other poorly understood aspects of disk physics.

    Viscously Spreading Accretion Disks around Black Holes: Implications for TDEs, LFBOTs and other Transients · 2026 · DOI

  • Some studies have made great efforts to remove any possible observational bias from their data to measure an intrinsic MBH–Mbulge normalization offset, though the results of these analyses can yield conflicting results.

    Gravitational-wave Measurement of the <i>M</i> <sub>BH</sub> – <i>M</i> <sub>bulge</sub> Intrinsic Scatter at High Redshift · 2026 · DOI

  • Violation of the Maldacena-Shenker-Stanford (MSS) chaos bound has been observed in various black hole spacetimes, but its physical origin remains unclear.

    A universal geometric mechanism for chaos-bound violations in black hole spacetimes · 2026

  • II inherits the status of the series’ relativistic implemen- tation: the F -multiplier is an ansatz, and a covariant formulation (the series’ principal open problem) could in principle couple dimensional structure to geometry in ways not captured here—e.

    Radial Dimensionality Theory V: Black Holes and the Vacuum Nulling Prescription · 2026 · DOI

  • 1. The clean sample is limited to SXS nonspinning, quasi-circular simulations with q ≥ 0.05. 2. The high-J, low-q region is sparsely sampled, and the true EMRI limit is not tested. 3. J and u are algebraic transforms of η, not independent physical variables. 4. The square-law coe(cid:30)cients e1, s1 are leading-order near-apex values; higher-order (u2) terms are required away from equal mass (Appendix A). 5. The constants 10 √ 2 and π are suggestive scales, not established exact constants. 6. The result does not replace calibrated numerical-relativity remnant formulae.

    Reduced-Mass Branch Geometry of Nonspinning Binary Black Hole Remnants · 2026 · DOI

  • In this work, we have studied shockwaves arising from ultra-relativistic boosts of electrically charged black holes in Einstein–Maxwell effective field theory. Working to linear order in the Wilson coefficients, we derived the EFT corrections to the charged shockwave geometry and computed the time delay experienced by a probe photon traversing it. A key find- ing is that two contributions neglected in previous analyses are essential for obtaining a physically meaningful result: the EFT corrections to the shockwave metric itself, and the metric perturbation sourced by the interaction of the probe photon with the electromag- netic shockwave background. Only when both effects are included does the total time delay remain invariant under field redefinitions of the metric, as required for consistency within the EFT framework. There are actually cases where the backreaction effects can bring the first non-vanishing contributions to the time delay generated by certain EFT operators. For instance, in the 5D Einstein–Maxwell EFT, the RµνρσRµνρσ operator can not be removed in the minimal operator basis because the Gauss–Bonnet term is no longer a boundary term. While this operator is not probed by the photon equation of motion on the unperturbed shockwave metric [19], its contribution through the perturbative corrections to the shockwave metric (i.e. the backreaction effect) induces a dependence of the full time delay. It would also be interesting to consider the effects of not rescaling the black hole mass and charge with the boost parameter: as shown in Ref. [19], this would allow one to study the near-horizon regime of extremal black holes. We leave the study of this different limit for future work. An immediate next step is to compute the remaining s-channel contribution from O6, which requires solving the perturbed Einstein equations on the shockwave background. Completing this calculation will provide the full EFT-corrected time delay for charged shockwaves in Einstein–Maxwell theory. It is also instructive to compare our results with those obtained from on-shell amplitude methods. For purely gravitational shockwaves, Ref. [9] demonstrated that the classical time delay can be extracted by cutting the tree-level four-point amplitude. In the presence of both electromagnetic and gravitational fields, however, the amplitude structure becomes – 21 – richer: the relevant discontinuities arise from cuts of loop-level amplitudes, as illustrated in the analysis of Ref. [47]. Matching our shockwave calculation with this amplitude-based approach would provide a non-trivial cross-check of how classical observables emerge from EFT scattering amplitudes. With the complete expression for the time delay in hand, one can systematically ex- plore the resulting causality bounds on the Einstein–Maxwell EFT. These bounds offer a complementary probe of the UV consistency of gravity–gauge systems and may shed further light on conjectures such as weak gravity.

    Shockwaves and time delays in Einstein-Maxwell effective field theory · 2026 · DOI

  • The major- ity of them can either be rejected or they are deemed too rare (an SMBH spin flip following binary coalescence, or a giant-star TDE) to warrant further exploration at this stage in the absence of supporting evidence.

    SDSS J110546.07+145202.4: The First Long-duration Radio Changing-look NLS1 Galaxy · 2026 · DOI

  • In this work, we have shown how Bondi accretion is more sensitive to spacetime geometry and the EoS of the fluid than the NT accretion model. This makes the Bondi accretion model a better discriminant for distinguishing RBHs from classical solutions18. For a dark fluid, the standard sonic-point analysis must be modified due to the vanishing sound speed. For an exponential profile, critical points are well-defined for all RBHs, but not for Schwarzschild or Schwarzschild-de Sitter geometries. When applied to the SV family19, the Bondi model reveals that the location of the critical point and the luminosity profiles at small radius are primarily controlled by the parameter ℓ, while the electric charge acts as a subleading perturbation (≲ 3%). Wormhole configurations are topologically distinct. Not only do they exhibit a luminosity minimum at the throat (x = 0), which cannot be May 5, 2026 1:50 ws-ijmpa Bondi and Novikov-Thorne accretion in regular black holes and Simpson-Visser spacetimes 7 Fig. 2. Bondi luminosity L(x) as a function of x in the SV spacetime (M = 1 AU, η = 0.1). Upper panels: neutral SV (Q = 0). Lower panels: charged SV (Q = 0.3). Left column (barotropic fluid, C1 = 10, C3 = 1.9): luminosity profiles for w = 0 and w = 1, from ℓ = 0 to ℓ = 2.5, with wormhole profiles extended symmetrically to negative x. Increasing the value of ℓ results in a slower decline of the profiles as they move inward towards the accretion disc. The solutions remain nearly superposed with only a few exceptions. Right column (exponential profile, C4 = 2.1, r0 = 10 AU, ρ0 = 0.5 and 1.0 AU−2) Here, the luminosity exhibits a local minimum, followed by an increase to the horizon or throat. The inner region demonstrates the greatest sensitivity to both ℓ and the EoS, and thus to ρ0. In all panels, the charged and neutral profiles are very similar. reproduced by any BH geometry, but they also show the greatest deviations from classical solutions, reaching almost ∼ 30%. Several natural extensions of this work are currently under investigation, such as generalisation to rotating spacetimes for comparison with EHT observations, for which spin estimates are available. A second direction involves the matter sector: alternative dark matter distributions may lead to different predictions in terms of both sonic radius and emitted luminosity 25. Instead, the results obtained for both neutral and charged SV solutions motivated the study of additional hairy parameters, magnetically charged configurations, particle productions 26 and nonlinear electrodynamics couplings and repulsive gravitational effects arising in the exterior regions of regular spacetimes7,27. On the observational side, the numerical signatures identified here may become accessible with future instruments. GRMHD simulations, combined with next-generation imaging by the EHT, could help determine whether the phenomenology of the accretion of astrophysical compact objects is more accurately described by regular or classical BH spacetimes.

    Bondi and Novikov-Thorne accretion in regular black holes and Simpson-Visser spacetimes · 2026 · DOI

  • Extreme mass-ratio inspirals (EMRIs) with secondary objects following periodic or nearly-periodic orbits have been identified as key LISA sources, but the modification to EMRI gravitational waveforms resulting from EFT deviations has not been characterized. Computing the accumulated phase shifts and amplitude modulations in GW signals from EMRIs in effective field theory spacetimes would enable constraints on EFT coupling constants from future observations.

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

  • The connection between rational orbits and quasi-periodic oscillation resonances observed in accretion disks around black holes has been established in several gravity theories, but this relationship has not been explored specifically for periodic orbits in EFT extensions of general relativity. Mapping the correspondence between stable periodic orbits in EFT spacetimes and observed QPO frequencies would provide a testable bridge between orbital mechanics and high-energy astrophysics.

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

  • While the references document periodic orbits in numerous modified gravity theories (Horndeski theory, Einstein-Æther theory, Horava-Lifshitz gravity, quantum-corrected spacetimes), a systematic comparison of gravitational radiation signatures across these distinct EFT frameworks has not been performed. Direct numerical comparisons of gravitational wave spectra from periodic orbits in different effective field theory extensions would clarify which modifications are detectable by space-based observatories.

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

  • The paper examines periodic orbits around black holes in effective field theory extensions of general relativity, but the gravitational radiation emission rates from these orbits have not been computed across different EFT coupling parameters. Systematic calculations of energy loss rates and waveform characteristics as functions of the EFT deformation parameters are needed to enable observational tests with LISA, TianQin, and Taiji gravitational wave detectors.

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

  • Upper limits on normalizations of intercombination and forbidden lines for blueshifted O VII emission limit the precision of plasma diagnostics for the fast outflow component.

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

  • A precession of the outflows similar to that observed in SS433 may be present in NGC 5204 X-1, but cannot be robustly verified with current data quality.

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

  • Dormant BH binaries like Gaia BH1 and Gaia BH2 significantly outnumber their close, X-ray bright cousins, but their formation pathways remain uncertain.

    A red giant orbiting a black hole · 2023 · DOI

  • However, many repeating nuclear transients produced by tidal heating-induced mass loss are likely fainter than those detected thus far, and remain to be discovered.

    Mass Transfer in Tidally Heated Stars Orbiting Massive Black Holes and Implications for Repeating Nuclear Transients · 2026 · DOI

  • We propose that interactions between soft seed photons and an extended outflow located outside the magnetosphere can account for the observed hard lags, although the physical origin of the transient soft lags remains uncertain.

    Unveiling hidden millihertz quasi-periodic oscillations in 1A 0535+262 · 2026 · DOI

  • There is currently no consensus about what determines the presence or absence of the BBN or what generates the QPOs.

    Disk warping and black hole X-ray binaries. I. Tentative unification of low-frequency quasi-periodic oscillations · 2026 · DOI

  • High-quality data are available in the high-Eddington-fraction hard-intermediate state, the hard-to-soft transition, the soft state, and the poorly studied back transition to the dim hard state, making it an ideal dataset for comparing the accretion flow at vastly different accretion rates.

    Systematic Assessment of Disk Truncation in the Black Hole X-Ray Binary Swift J1727.8–1613 Using NICER · 2026 · DOI

  • The imaginary part of the modes exhibits comparatively weaker dependence on the halo parameter; the physical mechanisms governing this weaker dependence warrant further investigation.

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

  • The analytic approximation using 1/ℓ expansion is highly accurate for ℓ ≥ 3, but for ℓ = 2, while the error remains small, this represents a limitation in the applicability range of the derived formulas.

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

  • The signal-to-noise ratio of individual observations is insufficient to robustly track Doppler shifts as a function of time to detect secular or quasi-periodic variations in the outflow components.

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

Most-cited papers in Astrophysical Phenomena and Observations

Most recent work

Find a gap in your own Astrophysical Phenomena and Observations sub-topic

This page shows what the Astrophysical Phenomena and Observations literature already flags as unresolved. To narrow it to your specific question, run the guided finder — it searches the gap library on demand and checks candidates against 250M+ OpenAlex works.

Open the Research Gap Finder →

Related topics in Physics and Astronomy

Stellar, planetary, and galactic studies
92 open questions
Model Reduction and Neural Networks
84 open questions
Cosmology and Gravitation Theories
76 open questions
Galaxies: Formation, Evolution, Phenomena
76 open questions
Quantum Mechanics and Applications
68 open questions
Ionosphere and magnetosphere dynamics
60 open questions
Astrophysics and Star Formation Studies
54 open questions
Particle physics theoretical and experimental studies
50 open questions
28 open questions have been extracted from the limitations and future-work passages of 355 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.

Tools for your next paper

Gaps & Literature SearchFind open questions in any field — 120,000+ open gaps mined from our own library.Pre-CheckIs your paper ready? A Tier 1–5 acceptance probability in seconds.Journal FinderA ranked shortlist of target journals from a 17,500-venue index.Duplicate Publication CheckerCheck prior-publication & salami-slicing risk across 8 sources.Citation GeneratorFreeA DOI or title → APA, MLA, Vancouver, Chicago, BibTeX, RIS. No signup.Graphical Abstract MakerFreeTurn your findings into a colorblind-safe graphical abstract.

Compare the category — Honest roundups of the AI research tools, ours listed alongside the alternatives.

Command palette

Jump anywhere, run any action.