Universe

A complete classification is conducted of the exact solutions of Maxwell vacuum equations for invariant electromagnetic fields in null homogeneous Petrov spaces with non-solvable groups of motions $G_3$, acting simply transitively on null hypersurfaces of null homogeneous Petrov spaces. The classification of exact solutions to Maxwell vacuum equations is based on using the representation of components of the contravariant metric tensor and components of the invariant electromagnetic field in terms of the vector fields of a canonical frame. The classification results are presented in a form convenient for further use.

We present a plane-of-sky observational analysis of a solar eruptive event that occurred on 2 September 2023. The flare peaked at approximately 07:00 UT, closely aligning with the impulsive acceleration phase of the erupting flux rope, which accelerated from an initial speed of 42 km s⁻¹ to 501 km s⁻¹. The associated coronal mass ejection (CME) propagated through interplanetary space at a near-constant speed of 519 km s⁻¹, suggesting that its kinetic energy was primarily acquired within the lower solar atmosphere. Comparison of the projected propagation directions of the erupting flux rope and the CME reveals an apparent angular offset of approximately $10°$, which is interpreted through Potential Field Source Surface (PFSS) modeling as the result of asymmetric magnetic pressure gradients. Notably, the overlying coronal loops exhibited a piecewise acceleration, with the velocity increasing from approximately 7 km s⁻¹ to 320 km s⁻¹. Furthermore, the passage of the eruption-induced disturbance triggered large-amplitude, damped vertical oscillations in an adjacent prominence. Applying magnetohydrodynamic (MHD) prominence seismology based on Hyder’s model, we derive a local radial magnetic field strength of 1.77–7.02 G. These results provide a detailed view of the evolution from magnetic energy release to large-scale coronal disturbances and the subsequent prominence oscillation.

Several minimal-length constructions deform the spacetime metric conformally at leading order, . We ask which observables can register such a deformation. The two structural results rest on standard properties of conformal rescalings; what is worked out here is their consequence for this class of metrics, carried to closed form on a black-hole background. For an arbitrary conformal factor the unparametrized null geodesics are unchanged, so the critical impact parameter, the shadow angular radius seen from infinity, the deflection angles and the Shapiro delay keep their undeformed values at all orders, and the photon sphere keeps its coordinate location although its areal radius changes. A minimally coupled massless test scalar on $\tilde{g}$ obeys, exactly, a wave equation on g with the single potential , into which the Weyl invariant does not enter; a conformally coupled massless scalar does not see the deformation at all. For a Reissner–Nordström background and the power-law family $\eta ={\epsilon }_0{(M/r)}^p$, with p as a model input rather than a prediction, we obtain the leading large-l scalar quasinormal shift , suppressed as $l^{-2}$, and closed forms for the ISCO radius, the disk radiative efficiency and the orbital frequency. Within this family the channels fall silent at the distinct exponents $p=3$, 2 and $5/2$. All results are checked by computer algebra.