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1. Inside the Stagnation Radius of the Nearest Billion-solar-mass Black Hole

   https://doi.org/10.3847/1538-4357/adfa93  

   Wrobel, J M; Pesce, D W; Nyland, K E (September 2025, The Astrophysical Journal)

   Abstract We used the NSF Jansky Very Large Array at a frequencyν = 22 GHz to study the nearest billion-solar-mass black hole (BH), in the early-type galaxy NGC 3115 at a distance of 9.7 Mpc. We localize a faint continuum nucleus, with flux densityS_{22 GHz} = 48.2 ± 6.4μJy, to a FWHM diameterd_{22 GHz} < 59 mas (2.8 pc). We find no evidence for adjacent emission within a stagnation region of radiusR_sta ∼ 360 mas (17 pc) identified in a recent hydrodynamic simulation tailored to NGC 3115. Within that region, the simulated gas flow developed into an advection-dominated accretion flow (ADAF). The nucleus’ luminosity densityL_{22 GHz} = 5.4 × 10¹⁷W Hz⁻¹is about 60 times that of Sagittarius A^⋆. The nucleus’ spectral index ${\alpha }_{10\mathrm{GHz}}^{22\mathrm{GHz}}=-1.85\pm 0.18$ (S_ν ∝ ν^α) indicates optically thin synchrotron emission. The spectral energy distribution of the nucleus peaks nearν_peak = 9 GHz. Modeling this radio peak as an ADAF implies a BH massM_ADAF = (1.2 ± 0.2) × 10⁹M_⊙, consistent with previous estimates of (1–2) × 10⁹M_⊙from stellar or hot-gas dynamics. Also, the Eddington-scaled accretion rate for NGC 3115, ${\dot{M}}_{\mathrm{ADAF}}/{\dot{M}}_{\mathrm{Edd}}=1.2_{-0.6}^{+1.0}\times 10^{-8}$ , is about 4–8 times lower than recent estimates for Sagittarius A^⋆. 

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2. A JWST View of the Overmassive Black Hole in NGC 4486B

   https://doi.org/10.3847/2041-8213/adf728  

   Tahmasebzadeh, Behzad; Taylor, Matthew A; Valluri, Monica; Yoshino, Haruka; Vasiliev, Eugene; Drinkwater, Michael J; Thompson, Solveig; Dage, Kristen; Côté, Patrick; Ferrarese, Laura; et al (August 2025, The Astrophysical Journal Letters)

   Abstract We present a new stellar dynamical measurement of the supermassive black hole in the compact elliptical galaxy NGC 4486B, based on integral field spectroscopy with JWST/NIRSpec. The two-dimensional kinematic maps reveal a resolved double nucleus and a velocity dispersion peak offset from the photometric center. Utilizing two independent methods—Schwarzschild orbit-superposition and Jeans anisotropic modeling—we tightly constrain the black hole mass by fitting the full line-of-sight velocity distribution. Our axisymmetric Schwarzschild models yield a best-fit black hole mass of ${\mathcal{M}}_{\mathrm{BH}}$ $=3.6_{-0.7}^{+0.7}\times 10^{8}M\odot$ , slightly lower but significantly more precise than previous estimates. However, since our models do not account for the nonequilibrium nature of the double nucleus, this value may represent a lower limit. Across all tested dynamical models, the inferred ${\mathcal{M}}_{\mathrm{BH}}$ /M_*ratio ranges from ∼4% to 13%, providing robust evidence for an overmassive SMBH in NGC 4486B. Combined with the galaxy’s location deep within the Virgo Cluster, our results support the interpretation that NGC 4486B is the tidally stripped remnant core of a formerly massive galaxy. As the JWST/NIRSpec field of view is insufficient to constrain the dark matter halo, we incorporate archival ground-based long-slit kinematics extending to 5″. While this provides some leverage on the dark matter content, the constraints remain relatively weak. We place only an upper limit on the dark matter fraction, with ${\mathcal{M}}_{\mathrm{DM}}$ / ${\mathcal{M}}_{*}$ ≲0.5 within 1 kpc—well beyond the effective radius. The inferred black hole mass remains unchanged with or without a dark matter halo. 

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3. On the Formation of S stars from a Recent Massive Black Hole Merger in the Galactic Center

   https://doi.org/10.3847/2041-8213/addc5d  

   Akiba, Tatsuya; Naoz, Smadar; Madigan, Ann-Marie (July 2025, The Astrophysical Journal Letters)

   Abstract The Galactic center hosts a rotating disk of young stars between 0.05 and 0.5 pc of Sgr A*. The “S stars” at a distance <0.04 pc, however, are on eccentric orbits with nearly isotropically distributed inclinations. The dynamical origin of the S-star cluster has remained a theoretical challenge. Using a series ofN-body simulations, we show that a recent massive black hole merger with Sgr A* can self-consistently produce many of the orbital properties of the Galactic nuclear star cluster within 0.5 pc. A black hole merger results in a gravitational-wave recoil kick, which causes the surrounding cluster to form an apse-aligned eccentric disk. We show that stars near the inner edge of an eccentric disk migrate inward and are driven to high eccentricities and inclinations due to secular torques similar to the eccentric Kozai–Lidov mechanism. In our fiducial model, starting with a thin eccentric disk withe= 0.3, the initially unoccupied region within 0.04 pc is populated with high-eccentricity, high-inclination S stars within a few Myr. This formation channel requires a black hole of mass $2_{-1.2}^{+3}\times 10^5{M}_{\odot }$ to have merged with Sgr A* within the last 10 Myr. 

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4. 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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5. Search for Neutrino Emission from Hard X-Ray AGN with IceCube

   https://doi.org/10.3847/1538-4357/ada94b  

   Abbasi, R; Ackermann, M; Adams, J; Agarwalla, S K; Aguilar, J A; Ahlers, M; Alameddine, JM; Amin, N M; Andeen, K; Argüelles, C; et al (March 2025, The Astrophysical Journal)

   Abstract Active galactic nuclei (AGN) are promising candidate sources of high-energy astrophysical neutrinos, since they provide environments rich in matter and photon targets where cosmic-ray interactions may lead to the production of gamma rays and neutrinos. We searched for high-energy neutrino emission from AGN using the Swift-BAT Spectroscopic Survey catalog of hard X-ray sources and 12 yr of IceCube muon track data. First, upon performing a stacked search, no significant emission was found. Second, we searched for neutrinos from a list of 43 candidate sources and found an excess from the direction of two sources, the Seyfert galaxies NGC 1068 and NGC 4151. We observed NGC 1068 at flux ${\varphi }_{{\nu }_{\mu }+{\overline{\nu }}_{\mu }}$ = $4.02_{-1.52}^{+1.58}\times 10^{-11}$ TeV⁻¹cm⁻²s⁻¹normalized at 1 TeV, with a power-law spectral indexγ= 3.10 ${}_{-0.22}^{+0.26}$ , consistent with previous IceCube results. The observation of a neutrino excess from the direction of NGC 4151 is at a posttrial significance of 2.9σ. If interpreted as an astrophysical signal, the excess observed from NGC 4151 corresponds to a flux ${\varphi }_{{\nu }_{\mu }+{\overline{\nu }}_{\mu }}$ = $1.51_{-0.81}^{+0.99}\times 10^{-11}$ TeV⁻¹cm⁻²s⁻¹normalized at 1 TeV andγ= 2.83 ${}_{-0.28}^{+0.35}$ . 

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