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1. Magnetogram-matching Biot–Savart Law and Decomposition of Vector Magnetograms

   https://doi.org/10.3847/1538-4357/add895  

   Titov, Viacheslav S; Downs, Cooper; Török, Tibor; Linker, Jon A; Prazak, Michael; Qiu, Jiong A (July 2025, The Astrophysical Journal)

   Abstract We generalize a magnetogram-matching Biot–Savart law (BSl) from planar to spherical geometry. For a given coronal current densityJ, this law determines the magnetic field $\tilde{\mathit{B}}$ whose radial component vanishes at the surface. The superposition of $\tilde{\mathit{B}}$ with a potential field defined by a given surface radial field,B_r, provides the entire configuration whereB_rremains unchanged by the currents. Using this approach, we (1) upgrade our regularized BSls for constructing coronal magnetic flux ropes (MFRs) and (2) propose a new method for decomposing a measured photospheric magnetic field as $\mathit{B}={\mathit{B}}_{\mathrm{pot}}+{\mathit{B}}_T+{\mathit{B}}_{\tilde{S}}$ , where the potential,B_pot, toroidal,B_T, and poloidal, ${\mathit{B}}_{\tilde{S}}$ , fields are determined byB_r,J_r, and the surface divergence ofB–B_pot, respectively, all derived from magnetic data. OurB_Tis identical to the one in the alternative Gaussian decomposition by P. W. Schuck et al., whileB_potand ${\mathit{B}}_{\tilde{S}}$ are different from their poloidal fields ${\mathit{B}}_{\mathrm{P}}^{<}$ and ${\mathit{B}}_{\mathrm{P}}^{>}$ , which arepotentialin the infinitesimal proximity to the upper and lower side of the surface, respectively. In contrast, our ${\mathit{B}}_{\tilde{S}}$ has no such constraints and, asB_potandB_T, refers to thesameupper side of the surface. In spite of these differences, for a continuousJdistribution across the surface,B_potand ${\mathit{B}}_{\tilde{S}}$ are linear combinations of ${\mathit{B}}_{\mathrm{P}}^{<}$ and ${\mathit{B}}_{\mathrm{P}}^{>}$ . We demonstrate that, similar to the Gaussian method, our decomposition allows one to identify the footprints and projected surface-location of MFRs in the solar corona, as well as the direction and connectivity of their currents. 

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2. Bridging Scales in Black Hole Accretion and Feedback: Magnetized Bondi Accretion in 3D GRMHD

   https://doi.org/10.3847/2041-8213/ad1048  

   Cho 조, Hyerin 혜린; Prather, Ben S.; Narayan, Ramesh; Natarajan, Priyamvada; Su, Kung-Yi; Ricarte, Angelo; Chatterjee, Koushik (December 2023, The Astrophysical Journal Letters)

   Abstract Fueling and feedback couple supermassive black holes (SMBHs) to their host galaxies across many orders of magnitude in spatial and temporal scales, making this problem notoriously challenging to simulate. We use a multi-zone computational method based on the general relativistic magnetohydrodynamic (GRMHD) code KHARMA that allows us to span 7 orders of magnitude in spatial scale, to simulate accretion onto a non-spinning SMBH from an external medium with a Bondi radius ofR_B≈ 2 × 10⁵GM_•/c², whereM_•is the SMBH mass. For the classic idealized Bondi problem, spherical gas accretion without magnetic fields, our simulation results agree very well with the general relativistic analytic solution. Meanwhile, when the accreting gas is magnetized, the SMBH magnetosphere becomes saturated with a strong magnetic field. The density profile varies as ∼r⁻¹rather thanr^−3/2and the accretion rate $\dot{M}$ is consequently suppressed by over 2 orders of magnitude below the Bondi rate ${\dot{M}}_{\mathrm{B}}$ . We find continuous energy feedback from the accretion flow to the external medium at a level of $\sim {10}^{-2}\dot{M}{c}^2\sim 5\times {10}^{-5}{\dot{M}}_{\mathrm{B}}{c}^2$ . Energy transport across these widely disparate scales occurs via turbulent convection triggered by magnetic field reconnection near the SMBH. Thus, strong magnetic fields that accumulate on horizon scales transform the flow dynamics far from the SMBH and naturally explain observed extremely low accretion rates compared to the Bondi rate, as well as at least part of the energy feedback. 

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3. Jets with a Twist: The Emergence of FR0 Jets in a 3D GRMHD Simulation of Zero-angular-momentum Black Hole Accretion

   https://doi.org/10.3847/1538-4357/ad0974  

   Lalakos, Aretaios; Tchekhovskoy, Alexander; Bromberg, Omer; Gottlieb, Ore; Jacquemin-Ide, Jonatan; Liska, Matthew; Zhang, Haocheng (March 2024, The Astrophysical Journal)

   Abstract Spinning supermassive black holes (BHs) in active galactic nuclei magnetically launch relativistic collimated outflows, or jets. Without angular momentum supply, such jets are thought to perish within 3 orders of magnitude in distance from the BH, well before reaching kiloparsec scales. We study the survival of such jets at the largest scale separation to date, via 3D general relativistic magnetohydrodynamic simulations of rapidly spinning BHs immersed into uniform zero-angular-momentum gas threaded by a weak vertical magnetic field. We place the gas outside the BH sphere of influence, or the Bondi radius, chosen to be much larger than the BH gravitational radius,R_B= 10³R_g. The BH develops dynamically important large-scale magnetic fields, forms a magnetically arrested disk (MAD), and launches relativistic jets that propagate well outsideR_Band suppress BH accretion to 1.5% of the Bondi rate, ${\dot{M}}_{\mathrm{B}}$ . Thus, low-angular-momentum accretion in the MAD state can form large-scale jets in Fanaroff–Riley (FR) type I and II galaxies. Subsequently, the disk shrinks and exits the MAD state: barely a disk (BAD), it rapidly precesses, whips the jets around, globally destroys them, and lets 5%–10% of ${\dot{M}}_{\mathrm{B}}$ reach the BH. Thereafter, the disk starts rocking back and forth by angles 90°–180°: the rocking accretion disk (RAD) launches weak intermittent jets that spread their energy over a large area and suppress BH accretion to ≲2% ${\dot{M}}_{\mathrm{B}}$ . Because the BAD and RAD states tangle up the jets and destroy them well insideR_B, they are promising candidates for the more abundant, but less luminous, class of FR0 galaxies. 

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4. The Origin of Da Scaling: Suppressed Cooling in Fast-cooling Mixing Layers

   https://doi.org/10.3847/1538-4357/ae908e  

   Lancaster, Lachlan; Fielding, Drummond; Mohapatra, Rajsekhar; Bryan, Greg L (August 2026, The Astrophysical Journal)

   Abstract In numerical experiments simulating turbulent radiative mixing layers (TRMLs), it is observed that as the cooling time in the mixed gas,t_cool, becomes very short compared to the dynamical time of the turbulence,t_eddy/t_cool ≫ 1, there is a change in the scaling behavior of the total energy radiated in the TRML as a function of this ratio, also known as the Damköhler number, Da ≡ t_eddy/t_cool, from ${\dot{E}}_{\mathrm{cool}}\propto {\mathrm{Da}}^{1/2}$ to ${\dot{E}}_{\mathrm{cool}}\propto {\mathrm{Da}}^{1/4}$ . The latter, so-called “fast-cooling,” regime is of particular interest, as many astrophysical mixing layers lie in this regime. We demonstrate that the origin of this change is the suppression of turbulent folding of the surface by the ram-pressure of the inflowing gas, which becomes much greater than the turbulent pressure in this regime. We present an argument that reproduces the ${\dot{E}}_{\mathrm{cool}}\propto {\mathrm{Da}}^{1/4}$ behavior by appealing to the suppression of the fractal structure of the interface by the ram-pressure of the inflowing gas. 

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5. Measurement of CP asymmetry in $$ {\textrm{B}}_{\textrm{s}}^0\to {\textrm{D}}_{\textrm{s}}^{\mp }{\textrm{K}}^{\pm } $$ decays

   https://doi.org/10.1007/JHEP03(2025)139  

   Aaij, R; Abdelmotteleb, A_S W; Abellan_Beteta, C; Abudinén, F; Ackernley, T; Adefisoye, A A; Adeva, B; Adinolfi, M; Adlarson, P; Agapopoulou, C; et al (March 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> A measurement of theCP-violating parameters in$$ {B}_s^0\boldsymbol{\to}{D}_s^{\mp }{K}^{\pm} $$ $B_s^0\to D_s^{\mp }{K}^{\pm }$ decays is reported, based on the analysis of proton-proton collision data collected by the LHCb experiment corresponding to an integrated luminosity of 6 fb⁻¹at a centre-of-mass energy of 13 TeV. The measured parameters are obtained with a decay-time dependent analysis yieldingC_f= 0.791 ± 0.061 ± 0.022,$$ {A}_f^{\Delta \Gamma} $$ $A_f^{\text{∆}\Gamma }$ = −0.051 ± 0.134 ± 0.058,$$ {A}_{\overline{f}}^{\Delta \Gamma} $$ $A_{\overline{f}}^{\text{∆}\Gamma }$ = −0.303 ± 0.125 ± 0.055,S_f= −0.571 ± 0.084 ± 0.023 and$$ {S}_{\overline{f}} $$ $S_{\overline{f}}$ = −0.503 ± 0.084 ± 0.025, where the first uncertainty is statistical and the second systematic. This corresponds to CP violation in the interference between mixing and decay of about 8.6σ. Together with the value of the$$ {B}_s^0 $$ $B_s^0$ mixing phase −2β_s, these parameters are used to obtain a measurement of the CKM angleγequal to (74 ± 12)° modulo 180°, where the uncertainty contains both statistical and systematic contributions. This result is combined with the previous LHCb measurement in this channel using 3 fb⁻¹resulting in a determination of$$ \gamma ={\left({81}_{-11}^{+12}\right)}^{\circ } $$ $\gamma ={\left({81}_{-11}^{+12}\right)}^{\circ }$ . 

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