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    Disciplines / Research questions

    Astronomy

    92 research topics · 303 questions

    Three-dimensional magnetic reconnection1 questions

    1. Three-dimensional geometry and origin of secondary electron-scale reconnection at ion-scale flux-rope boundaries in Earth's magnetosphere

    The chromospheric heating problem1 questions

    1. Dominant heating mechanisms of the solar chromosphere: the mechanism partition of chromospheric energy deposition and its observational determination

    Magnetized interstellar medium not yet clearly detected3 questions

    1. Completing the arm-by-arm magnetic map of the Galactic disk: the number, locations, and three-dimensional geometry of large-scale field reversals from pulsar Faraday rotation

    2. Magnetic regulation of star formation in Central Molecular Zone clouds: robust field-star-formation correlations and field behavior from cloud to core scales

    3. Magnetic fields in the diffuse interstellar medium: a statistical 21-cm Zeeman census of the cold neutral medium, field amplification in superbubble walls, and the claimed linear polarization of the 21-cm line

    What is a magnetar2 questions

    1. Formation channel and internal magnetic-field structure of classical magnetars

    2. Joint determination of the Galactic magnetar formation rate and magnetic-field decay law from the observed population

    What is a black hole4 questions

    1. Practical measurement of the black-hole photon ring: separating lensed subimages from astrophysical emission in finite-resolution observations of M87* and Sgr A*

    2. Time-resolved (dynamical) imaging of event-horizon-scale structure in Sagittarius A* on orbital timescales

    3. Physical Origin of the Variability Discrepancy Between GRMHD Simulations and the Observed 230 GHz Emission of Sagittarius A*

    4. Practical reconstruction of a black hole photon ring's curve shape and intensity from interferometric visibility data

    The mysterious 21-micron dust feature4 questions

    1. Completing the carrier identification of the 21 μm emission feature in carbon-rich post-AGB stars: quantitative abundance-budget testing of the organic candidates

    2. Identification of the carriers of the unidentified 21 µm and 30 µm circumstellar dust emission features in carbon-rich post-AGB objects

    3. Robust correlations between gas-phase chemistry, physical conditions, and the 21 μm emission feature in protoplanetary nebulae

    4. The Carrier of the 21 Micron Emission Feature in Carbon-Rich Post-AGB Stars: Material Identification and Excitation Mechanism

    Measurement of the solar magnetic field3 questions

    1. Accurate coronal magnetic-field measurement from Hinode/EIS EUV spectra via the Fe X magnetic-field-induced transition (MIT): temperature diagnostics, joint inversion, and observational validation

    2. Completing multi-line forbidden-line single-point inversion for coronal vector magnetic fields: infrared Landé g-factors, line-of-sight validation, and degeneracy resolution

    3. Intrinsic radiality of the solar polar photospheric magnetic field: separating true geometry from inversion and resolution bias

    Topological singularities of the solar magnetic field4 questions

    1. Counting and locating magnetic null points and separators in anemone-type solar flares beyond unbalanced point-charge groups

    2. Topological instability criteria beyond four magnetic point sources: generalizing and validating the 'topological trigger' model of unipolar solar flares

    3. Bifurcation scenarios for separators and transitions between topological classes of global coronal magnetic fields in the point-charge model

    4. Null-like points in the coronal magnetic skeleton: correspondence with sub-photospheric-null QSL signatures and extension to force-free and MHD fields

    The solar dynamo7 questions

    1. Locating the solar magnetic poles: magnitude, stability, and origin of the misalignment between the Sun's magnetic axis and its rotation axis

    2. The toroidal-field amplitude problem of the solar flux-transport dynamo: reconciling saturation strength with active-region flux emergence

    3. Observational access to the Sun's dynamo-relevant subsurface toroidal magnetic field and quantitative multi-cycle testing of Babcock–Leighton flux-transport dynamo models

    4. Grand Minima of solar activity in realistic solar dynamo models: reproducing long-term statistics and validating them against proxy records

    5. Temporal memory of the solar dynamo: one-cycle precursor law versus persistent multi-cycle memory under Babcock–Leighton stochasticity

    6. Nonlinear viability and cycle closure of the near-surface magnetorotational-instability solar dynamo

    7. Physical origin of the phase relation between sunspot numbers and sunspot areas: connecting frequency-confined phase synchronization to solar dynamo theory

    High-resolution solar observations3 questions

    1. Unverified minimal scales of solar photospheric fine structure: intergranular-lane widths, thinnest flux-tube diameters, and the stationary magnetic-diffusion model of micropores and facular knots

    2. Origin of the unexplained ~48 nm RMS seeing-unrelated wavefront error limiting granulation contrast at the Swedish 1-m Solar Telescope

    3. Completing the point-spread-function characterization of the Solar Orbiter/EUI telescopes: diffraction fine-tuning, inversion uniqueness, anisotropy, spatial variation, and the uncharacterized HRI Lyman-alpha and Full Sun Imager channels

    Internal structure, flow fields, and magnetic fields of sunspots10 questions

    1. Formation, maintenance, and reversal of photospheric counter-Evershed flows in mature sunspot penumbrae

    2. Consistent, filter-independent helioseismic inference of sunspot subsurface thermal and magnetic structure (the open issues of the NOAA AR 9787 case study)

    3. Umbral dots and the depth of magnetic fragmentation of the sunspot umbra: monolithic versus cluster subsurface structure

    4. Physical origin of the invariant vertical magnetic field at the sunspot umbra–penumbra boundary and its joint reproduction with the Evershed flow in simulations

    5. Monolithic versus cluster subsurface magnetic structure of sunspots

    6. Sunspot anchoring and longevity: what subsurface depth and formation history sustain week-long sunspot lifetimes?

    7. Vertical stratification of the Evershed flow and fine-scale magnetic field in penumbral filaments during penumbral formation and decay

    8. Separating thermal and magnetic contributions to helioseismic wave-speed anomalies beneath sunspots, and the direct determination of sunspot subphotospheric magnetic geometry (the ~4 Mm shallow-sunspot expansion)

    9. Quantify and test whether magnetic-kinetic equipartition sets the termination of the photospheric Evershed flow at the outer penumbral boundary of sunspots across spot sizes and evolutionary phases

    10. Subsurface mass budget of the sunspot moat flow: the compensating upflows beneath the magnetised region and quantitative confrontation with MHD simulations

    Polar magnetic fields of the Sun6 questions

    1. Alfvén-wave transmission through the Sun's expanding polar flux tubes: quantitatively testing the 'magnetic chimney' conjecture for fast-solar-wind acceleration

    2. Separating intrinsic polar-field structure from observational bias in out-of-ecliptic measurements of the Sun's polar magnetic field

    3. Physical origin of the near-pole decline of solar polar-cap magnetic flux and the meridional-flow profile within the last 20 degrees of latitude

    4. Quantitative causal attribution of the hemispherically asymmetric solar polar-field evolution in Cycle 24: the weak post-reversal north-polar flux and the early southern polar maximum

    5. Direct confirmation, cycle dependence, and energetic role of the small-scale magnetic loop population inferred at the solar poles and limbs

    6. Local dynamo action in the solar polar caps: existence and origin

    What is the nature of the Sun's tachocline9 questions

    1. The shape of the solar tachocline: robust high-latitude determination, possible sharp latitudinal structure, and the implied interior magnetic field

    2. Testing the thermal-wind origin of the Sun's near-surface shear layer: the gradual rotation-influence transition, the high-latitude temperature anomaly, near-surface thermal wind balance, and the pole–equator temperature difference

    3. Dynamical origin of the solar-cycle time variations of the solar tachocline

    4. Origin of the solar near-surface shear layer: completing and testing the Λ-effect account

    5. Dynamo-action confinement of the solar tachocline: viability in the solar parameter regime and observational tests

    6. What confines the solar tachocline and maintains the uniform rotation of the Sun's radiative interior?

    7. Rotating and magnetized stratified horizontal-shear turbulence at low Prandtl number: regime boundaries, scaling laws, and the sign of turbulent angular-momentum transport in the solar tachocline

    8. Full-depth theory of the solar near-surface shear layer: origin of the radial shear and its driving of the global meridional circulation

    9. The physical origin of the Sun's near-surface shear layer

    Rotation and meridional flow structure inside the Sun8 questions

    1. The deep solar meridional circulation: confirming an equatorward return flow near the base of the convection zone and the mechanism of its magnetic modulation

    2. Reconciling Tracer, Doppler, and Helioseismic Measurements of the Solar-Cycle Variations of the Sun's Differential Rotation and Meridional Flow

    3. The deep structure of the Sun's meridional circulation: a physically consistent helioseismic determination of the radial and latitudinal flow robust against the center-to-limb systematic

    4. Long-term variations of the solar meridional circulation: secular evolution, hemispheric asymmetry, and the physical origin of multi-decadal flow changes

    5. Definitive measurement of the solar core rotation rate and its use as a calibration of magnetic angular-momentum transport in stellar radiative zones

    6. Helioseismic determination of the solar core rotation below r≈0.2 R⊙r\approx 0.2\,R_{\odot}: unambiguous detection of solar gravity modes and measurement of their rotational splittings

    7. The deep structure of the Sun's meridional circulation: number of cells stacked in depth, return-flow location, and cycle dependence

    8. Magnetically driven deep meridional circulation in the Sun: testing the gyroscopic-pumping upwelling predicted by cyclic convective dynamo simulations

    Meridional circulation inside the Sun8 questions

    1. Locating the equatorward return flow and radial cell structure of the Sun's meridional circulation

    2. Reconciling conflicting helioseismic inferences of the Sun's deep meridional circulation

    3. Time-dependent meridional circulation in the Sun and its role in the solar dynamo

    4. Prior-robust determination of the Sun's deep meridional-circulation morphology and of the operating angular-momentum-transport regime

    5. Robust helioseismic determination of the Sun's deep meridional circulation profile: resolving the single-cell versus multi-cell ambiguity with quantified systematics

    6. Definitive determination of the Sun's meridional circulation throughout the convection zone: cell structure, return-flow depth, temporal stability, and dynamo implications

    7. Single cell or multiple cells: the topology and return-flow depth of the Sun's deep meridional circulation

    8. The Deep Structure of the Sun's Meridional Circulation: Cell Number, Return-Flow Depth, and Robustness to Helioseismic Systematics

    Diagnosis of chromospheric magnetic field structure5 questions

    1. Formation-height ordering of the Hα and Ca II 854.2 nm line cores in chromospheric downflows and the magnetic-field stratification retrievable from simultaneous Stokes I and V spectropolarimetry

    2. Height expansion of plage chromospheric magnetic fields and their causal connection to localized chromospheric heating

    3. Calibrated statistical structure of sunspot magnetic fields between the photosphere and the upper chromosphere: He I 10830 Å formation heights and multi-spot generality

    4. Three-dimensional non-LTE Stokes inversion of the solar Mg II h & k lines with partial frequency redistribution and J-state interference for unambiguous chromospheric vector magnetometry

    5. Discriminating the geometry of the upper-chromospheric magnetic field in solar enhanced-network regions from full-Stokes Mg II h&k spectropolarimetry

    What is the basic structure of the solar chromosphere8 questions

    1. Generality and observational confirmation of in-situ magnetic-field amplification in the quiet solar chromosphere

    2. Do slender Ca II H fibrils chart magnetic fields in the low solar chromosphere? Identifying their heating mechanism, validating their field mapping, and fixing their formation heights

    3. The physical nature of internetwork H-alpha chromospheric fibrils and their MHD kink waves: magnetic connectivity, visibility cycles, wave damping, and magneto-seismology

    4. Robustness and observational testability of the shock–current-sheet heating partition in the quiet-Sun chromosphere

    5. The minimum temperature of the quiet solar chromosphere: do effectively non-magnetic, sub-2000 K cool pockets exist, or does quiet-Sun magnetic heating prevent them?

    6. Small-scale-dynamo energy budget of the quiet Sun: non-ideal chromospheric physics, network fields, and the sustainability of a steady corona

    7. Physical nature of the quiet-Sun chromosphere's fine structure: the mass and energy supply of network 'straws' (Type II spicules), near-network low-lying loops, and validated multi-dimensional radiative-dynamic modeling

    8. Quantitative determination of the quiet-Sun chromospheric magnetic field structure and its interaction with upward-propagating acoustic waves

    Measurements and physical interpretation of solar flare polarization spectra8 questions

    1. Origin of the linear polarization of the hydrogen Hα\alpha line in solar flares: can energetic-proton beams (or any particle-beam mechanism) reproduce the observed several-percent polarization under self-consistent NLTE polarized radiative transfer?

    2. Scattering polarization of chromospheric lines in realistic multi-dimensional models of solar flare ribbons

    3. Does the degree of circular polarisation at millimetre wavelengths diagnose the magnetic footpoint asymmetry of solar flare loops?

    4. Origin of high-frequency circular-polarization reversals in solar microwave bursts: quasi-transverse propagation versus intrinsic emission physics

    5. Full-Stokes inversion of the GRIS He I 10830 Å dataset of the 2023 July 16 C-class flare footpoints and the physical interpretation of the HAZEL enhancement factor β

    6. Physical origin of the linear-polarization depression in solar-flare plasma sheets: quantitative forward modeling of reconnection-driven depolarization and its forbidden-line diagnostics

    7. Interpreting the far-wing secondary Stokes V peaks around the He I D3 line at the seismic source of the 2003 October 28 solar flare: magnetic fields, plasma velocities, and polarization mechanism

    8. The true degree, temporal evolution, and physical origin of hard X-ray polarization in solar flares

    Solar radio emission mechanisms3 questions

    1. Sustaining the brightest solar radio bursts: the physical mechanism of hour-long, broadband electron cyclotron maser emission in solar post-flare loop systems and the origin of its less-than-100% polarization

    2. Emission mechanism of moving Type IV solar radio bursts: fundamental plasma emission versus electron-cyclotron maser emission at coronal heights above 1.15 solar radii

    3. Self-consistent kinetic simulation of double-plasma-resonance zebra-pattern emission in an inhomogeneous solar corona

    Overview of solar physics7 questions

    1. The coronal heating problem: identifying and quantifying the mechanism(s) that heat and sustain the solar corona

    2. The solar dynamo problem: identifying the mechanism of the Sun's large-scale magnetic cycle and the deep-convection discrepancy that constrains it

    3. Origin of the slow solar wind: source regions, magnetic topology, and release–acceleration mechanisms

    4. Do type-II spicules supply the mass and energy of the solar corona, and what is the physical nature of the spicule-associated propagating coronal disturbances?

    5. Quantitative role of Alfvén waves in heating and accelerating the young solar wind from different source regions

    6. Origin of solar grand minima: the unconstrained Babcock–Leighton poloidal source for very weak cycles in the observation-based iterative map

    7. Do picoflares dominate quiet-Sun coronal heating? The low-energy power-law slope of the impulsive EUV brightening energy distribution

    Origin of the solar system3 questions

    1. Validating Jupiter's proposed growth history: the proto-Jupiter gap as origin of the NC–CC meteorite isotopic dichotomy, paleomagnetic formation-distance constraints, and compatibility with planetary migration

    2. The physical mechanism of the solar nebula's terminal dispersal: magnetically driven winds, photoevaporation, and residual hydrodynamic accretion

    3. Quantitative physical modeling of volatile-element depletion in carbonaceous chondrites: gas-solid separation, nebular cooling, and transport of CI-like material in the solar nebula

    Small-scale solar magnetic fields8 questions

    1. Physical mechanism coupling the solar activity cycle to the minute-scale horizontal dynamics of photospheric magnetic elements

    2. Closing the quiet-Sun internetwork flux-cancellation heating budget: the contribution of undetected weak-field cancellations to chromospheric heating

    3. Closure of the sub-resolution quiet-Sun photospheric magnetic flux budget and the true flux turnover time

    4. Secular invariance of quiet-Sun small-scale magnetism and its contribution to multi-centennial Total Solar Irradiance variation

    5. Reconciling published estimates of the small-scale magnetic flux emergence rate in the quiet-Sun internetwork

    6. Origin and Full-Cycle Confirmation of the Latitude and Solar-Cycle Dependence of Quiet-Sun Internetwork Magnetic Fields

    7. Resolving the SINN–DeSIRe inversion discrepancy in the upper-photospheric horizontal-to-vertical field-strength ratio of the quiet-Sun internetwork (Sunrise III/SCIP)

    8. Genuine invariance or instrumental limits: are quiet-Sun internetwork magnetic fields solar-cycle dependent?

    Solar flares and magnetic field variations7 questions

    1. The physical origin of and connection between white-light emission and photospheric magnetic-field changes in solar flares

    2. Generality and mechanism of coronal magnetic-field decay as the energy source of solar flares

    3. Quantifying the relative contributions and causal ordering of the mechanisms that produce step-like photospheric horizontal magnetic field changes during solar flares

    4. Physical mechanism of the transient rotation of photospheric vector magnetic fields associated with a solar flare (SOL2015-06-22T18:23)

    5. Physical origin of flare-related stepwise magnetic-field changes in the lower solar atmosphere and the photosphere-chromosphere incoherence (Kleint 2017 open problem)

    6. Where is flare-related magnetic shear actually relieved? Height-dependent shear and free-energy redistribution and a quantitative test of photospheric line-tying in solar flares

    7. Corona–photosphere coupling in flare-driven Lorentz-force changes and prolonged penumbral decay

    Variation of solar neutrinos7 questions

    1. Can a single resonant spin-flavor-precession scenario with light sterile neutrinos simultaneously fit all solar neutrino data, and is the low-energy flux time-variable through magnetic effects?

    2. Physical origin of the residual total solar irradiance variability not explained by surface magnetism

    3. Time modulations of the solar 8^{8}B neutrino flux beyond the annual orbital effect: detection or exclusion at percent-level amplitudes

    4. Probing periodic modulations of the solar 8B neutrino flux below the 5% amplitude floor: magnetic-moment and resonant spin-flavor precession sensitivities and their interpretation

    5. Are solar gravity modes detectable in the solar neutrino flux? Quantitative amplitude prediction and short-period modulation sensitivity

    6. Search for sub-percent periodic modulations of the solar 7^7Be neutrino flux and the amplitude of the helioseismic g-mode coupling

    7. Impact of three-dimensional, time-dependent solar density perturbations (gravity modes) on solar neutrino flavor conversion and flux time variation

    Celestial reference system2 questions

    1. Origins, Correction, and Exploitation of Astrometric Position Variability of ICRF Radio Sources for the Next-Generation Celestial Reference Frame

    2. Open core of the Gaia optical celestial reference frame: quasar proper-motion systematics for gravitational-wave astrometry and the physical origin of radio–optical offsets with ICRF3

    Celestial mechanics: a story triggered by an apple3 questions

    1. Boundary between chaotic and regular motion in N-planet systems: full phase-space structure and the transition from local chaos to orbital instability

    2. Is one-dimensional advection-diffusion in a secular frequency representative of planetary systems beyond the Solar System, and what are their expected instability times?

    3. The expected dynamical lifetime of the inner Solar System: probability of catastrophic instability under a complete physical model

    Is turbulence chaotic? — Turbulence in the interstellar medium and star formation2 questions

    1. How stellar feedback reshapes the turbulence driving parameter of molecular clouds in disc galaxies

    2. Drivers and cross-scale coupling of the nonuniversal interstellar density spectra revealed by pulsar dispersion measures

    Turbulent motion and turbulence dynamo7 questions

    1. Unresolved Mach-number dependence of the turbulent dynamo: growth-rate and saturation asymptotics beyond Mach 20 and a predictive theory for supersonic, compressible turbulence

    2. Parameter regimes, high-magnetic-Reynolds-number behavior, and helicity interplay of the magnetic shear-current dynamo in sheared turbulence

    3. Saturation mechanism of the fluctuation dynamo in supersonic turbulent plasmas beyond the Pm ≥ 1, isothermal, solenoidally driven regime

    4. Survival of primordial seed magnetic fields and the observational identifiability of seed origin in low-turbulence cosmic regions

    5. Universality of phase-resolved turbulent dynamo diagnostics in the multiphase interstellar medium

    6. Quantitative theory and kinetic simulation of the fluctuation dynamo in a collisionless, weakly magnetized plasma: the effective-collision-rate regime sequence, saturation, and effective viscosities at intracluster-medium conditions

    7. Small-scale turbulent dynamo action in strongly supersonic, partially ionized molecular-cloud turbulence: growth rate, saturation level, and the attainability of equipartition within cloud lifetimes

    Ground observation and space exploration of asteroids2 questions

    1. Physically faithful joint inversion of asteroid optical and thermal-infrared photometry: nonconvex shapes, wavelength-dependent emissivity, and the roughness–thermal-inertia degeneracy

    2. Surface evolution and disruption of near-Sun asteroids (q≤0.15q\le 0.15 au): is the population bluing physical, which processes dominate resurfacing and destruction, and what is the incidence of perihelion mass loss?

    Identification of cluster member stars3 questions

    1. Completeness-corrected globular-cluster membership from Gaia astrometry in crowded cores and high-background fields

    2. Reliability of supervised random-forest open-cluster membership with Gaia data: training-set sensitivity, overlapping sub-clump decomposition, and generality of the empirical correlations

    3. Quantifying systematic uncertainties in Gaia-ESO 3D-kinematic membership probabilities for Galactic open and globular clusters

    The origin of mass segregation in star clusters3 questions

    1. Origin, survival, and stochasticity of early mass segregation during gas-rich hierarchical star cluster assembly

    2. Do star clusters form completely mass-segregated? Robustness of the primordial full-segregation conclusion for the Orion Nebula Cluster and the prevalence of near-complete primordial mass segregation among newborn clusters

    3. The origin of early mass segregation in young star clusters: dynamical subcluster-merger inheritance versus primordial segregation

    Metallicity of galaxies3 questions

    1. Separating the roles of metal-poor inflows and metal-enriched outflows in setting the ISM metallicity and effective yields of sub-Milky-Way galaxies

    2. Physical origin of the secondary star-formation-rate dependence of the galaxy mass–metallicity relation (the Fundamental Metallicity Relation) on the Te abundance scale

    3. The physical origin of the ~0.3 dex metallicity deficit of low-mass galaxies at high redshift: why galaxies of the same stellar mass are more metal-poor at z≳2z\gtrsim2 than at z∼0z\sim0

    Metallicity and chemical evolution of the intergalactic medium3 questions

    1. What drives the disappearance of the highly ionized circumgalactic medium at z≳5.7z\gtrsim 5.7: separating ionization evolution from early chemical impoverishment in reionization-era metal absorbers

    2. Reconciling chemical-enrichment models with the observed high-redshift intergalactic-medium abundance pattern ([C/H][{\rm C/H}], [Si/C][{\rm Si/C}], [O/C][{\rm O/C}]) and the transport of metals into the lowest-density regions

    3. Metal enrichment of the low-density intergalactic medium at z ≈ 3: incidence, faint-end C IV statistics, metallicities, and filling factors across multiple sightlines

    Mass function of galaxy clusters2 questions

    1. Unbiased halo-mass-function calibration and uncertainty propagation for next-generation galaxy cluster number-count cosmology

    2. Robust baryonic corrections to the halo mass function and halo bias for next-generation cluster cosmology

    Galaxy interactions and galaxy morphology3 questions

    1. Encounter dynamics and tidal response as functions of galaxy structure: generalizing the equal-mass twin-encounter mapping to realistic interactions and testing its diagnostic power

    2. Quantitative mapping between encounter physics and structural signatures of elliptical/lenticular (E/S0) galaxies in interacting pairs: calibrating CAS responses, merger clocks, and high-redshift dry-premerger selection

    3. The non-merger (environmental) channel of galaxy morphological transformation in dense environments and the observational validation of the merger-driven accounting

    Downsizing in galaxy formation and evolution1 questions

    1. The baryonic mapping problem of galaxy downsizing: which physical processes turn hierarchical dark-matter halo assembly into the observed downsizing in time of stellar-mass growth?

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