Evidence of a gravitational wave (GW) signal has emerged in pulsar timing array (PTA) data, opening a new window into the nanohertz GW Universe. We explore the physics of GW signals that may explain the data, with a focus on GW backgrounds (GWBs) considering both astrophysical and cosmological origins. We describe how: ▪ An astrophysical nanohertz GWB emerges as the superposition of individual signals from inspiraling massive black hole binaries. ▪ Environment coupling, eccentricity, and sparse sampling cause great uncertainty in the theoretical prediction of the supermassive black hole signal but also offer a way to determine the origin of the signal. ▪ PTA data offer unprecedented opportunities to constrain high-energy physics beyond the Standard Model by probing early Universe GWBs that originated during or after inflation. ▪ Different early Universe GWBs, typically created by nonlinear and out-of-equilibrium dynamics, can explain the PTA data (e.g., those from inflation scenarios, first-order phase transitions, or topological defects). ▪ The PTA detection of GWs opens a new window to explore the Universe, with profound implications for astrophysics and particle physics (probing, e.g., the equation of state of the early Universe, the origin of cosmological perturbations, the nature of dark matter, or whether exotic objects like primordial black holes or cosmic strings exist).

The Complex Kinematics of the Young Stars Orbiting the Supermassive Black Hole in the Galactic Center Can Be Explained by the Presence of an Intermediate-mass Companion of Sgr A*

Angular Dependence of Winds Launched in Cold and Hot Accretion Flows around Supermassive Black Holes

The Millimeter/X-Ray Relation in Rapidly Accreting Supermassive Black Holes at z < 0.16

From Dense Gas Clouds to Supermassive Black Hole Seeds: Hybrid Hydro/Direct N-body Simulations of Runaway Collision-driven Intermediate-mass Black Hole Formation

Multimessenger Probes of the Supermassive Black Hole Binary Population: The Role of Pulsar Timing Arrays

Supermassive black holes and their host galaxies grow together over time, producing correlations between the black hole mass and various galaxy properties. Determining the evolution of these correlations requires precise measurements of the masses of distant black holes. We observed the gravitationally lensed quiescent galaxy MRG-M0138 at redshift 1.95 using James Webb Space Telescope integral field spectroscopy to spatially resolve the kinematics of stars within the black hole's sphere of influence. By using a foreground lens model and fitting stellar dynamical models, we determined the mass of its inactive black hole to be [Formula: see text] solar masses. Comparing this measurement to local galaxies, we found that [Formula: see text] is higher than expected given the galaxy's bulge mass but consistent with the correlation of [Formula: see text] with stellar velocity dispersion.

Abstract Wind is a key mechanism for supermassive black hole (SMBH) feedback to their host galaxies. In tidal disruption events (TDEs), black holes spend most of their time accreting at highly sub-Eddington rates, implying that feedback from persistent sub-Eddington winds could be significant. We investigate the effects of black hole mass, viscosity parameter, and stellar debris temperature on the properties of winds from hot accretion flows in TDEs. We find that more massive black holes yield a higher accreted fraction and launch faster winds, while the debris temperature has a negligible influence on the accretion flow. For α = 0.1, the mildly relativistic unbound winds (∼0.1 c ) are launched predominantly from the outside of the accretion flows along the equatorial plane, with a kinetic energy of ∼10 −4 L Edd . In contrast, convective bound outflows dominate for α = 0.01, which differs from the true winds typically seen in active galactic nucleus and X-ray binaries. Potential applications for explaining delayed radio brightening in TDEs at ∼10 3 days and for searching for intermediate-mass black holes through radio and X-ray surveys are also discussed.

Proton Acceleration by Collisionless Shocks in Supermassive Black Hole Coronae: Implications for High-energy Neutrinos

Optimizing Optical Searches for Supermassive Black Hole Binaries in Active Galactic Nuclei Light Curves: Fourier versus Bayesian Periodicity Detection

In ref. arXiv:2507.07171, we demonstrate that the high-redshift supermassive black holes in the so-called “little red dots” discovered by James Webb Space Telescope (JWST) can be explained by the primordial black hole (PBH) clustering on small scales. In this paper, we present a comprehensive simulation of the successive PBH mergers within a cluster by solving the Smoluchowski coagulation equation. We derive the coagulation kernel considering both cases with and without the effects of mass segregation. Then we employ the Monte Carlo method to solve the equation, implementing the full-conditioning scheme using the discrete inverse transformation method. Our simulations determine the runaway timescales of clusters and the mass population evolution of PBHs across a wide range of cosmic redshifts, depending on the number of PBHs within the cluster and the associated density.

Predicting Potential Host Galaxies of Supermassive Black Hole Binaries Based on Stellar Kinematics in Archival IFU Surveys

Gravitational growth of supermassive black holes in the extremely dense environment of the early universe: the case of A2744-QSO1

In this work, we present the definitive unification between the 26- dimensional bosonic string model of Palumbo-Nardelli and the Nardelli-Miriam Theory of Everything (TOE) centered on the gravitational nexus phi _ { G N } . We demonstrate that the 26D action serves as the primordial source for 10-dimensional local dynamics, stabilized by a &amp;#8220;golden-locking&amp;#8221; mechanism that forces asymptotic convergence toward the golden attractor phi ^ { dot { langle } } approx 1 . 6 1 8 6 6 5 . By utilizing the Hardy-Ramanujan anchor (1729) and the 18throot stabilization, we isolate discrete numerical values (256, 4096, 1728) that ensure the stability of wormhole throats and the horizons of supermassive black holes, such as the Gargantua type. Our results confirm the self-referential and fractal nature of the theory, identifying the sixth power of the golden ratio left( phi ^ { 6 } approx 1 8 right) as the precision trigger for dimensional reduction.

The study of the dark and abundantly existing component of matter in our universe remains one of the important challenges of modern astrophysics. It affects cosmic dynamics through its gravitational attraction to galactic systems. Due to its relevance in controlling galactic formations, its relationship with supermassive cores of galactic systems, such as black holes, is worthwhile to study. In this respect, this work explores an astrophysical correspondence of black holes and dark matter using the Einasto density distribution. In particular, we fuzzify the Hayward metric and construct analytical solutions describing self-gravitational compact interiors for different values of the shape parameter. We show that coupling of an anisotropic fluid distribution with de Sitter and nonlocal equations of state enables us to develop diverse stellar objects, including compact droplets (horizonless) and stellar black holes. The assumption of a nonlocal equation of state provides a unique class of fuzzified stellar configurations within the dynamics of general relativity. The presented relativistic exact solutions can be used to model supermassive galactic black holes.

Relativistic jets from supermassive black holes in active galactic nuclei are amongst the most powerful phenomena in the universe. Similar jets from stellar-mass black holes offer a chance to study the phenomena on accessible observation time scales. However, such comparative studies across black hole masses and time scales remain hampered by the long-standing perception that stellar-mass black hole jets are in a less relativistic regime. Here, we show the detection of two distinct, relativistic jet ejections from the Galactic black hole X-ray binary 4U 1543-47 during a single outburst, with radio interferometry monitoring observations. Our measurements reveal a likely Lorentz factor of approximately 8 and a minimum of 4.6 at launch with 95% confidence, demonstrating that stellar-mass black holes in X-ray binaries can launch jets as relativistic as those seen in active galactic nuclei.

The Impact of Supermassive Black Holes on Exoplanet Habitability. I. Spanning the Natural Mass Range

The supermassive black hole (Sgr A*) in the Galactic center is surrounded by the S-star cluster consisting of young stars on eccentric orbits. Recently, the an S-star binary system, called D9, was found. Its detection was based on periodic emission in Brackettγ (Brγ). Since Brγ is considered a signature of accretion, this emission could originate from the interaction of a binary and its circumbinary disk. However, due to the gravitational interaction between Sgr A* and the binary, the disk could be short-lived. We investigated the evolution of the disk around a stellar binary while orbiting Sgr A*. We used the framework for coupling a gravity solver (for the binary and Sgr. A*) with a hydrodynamics solver (for the disk). AMUSE We find that, irrespective of the initial disk inner and outer radii, it eventually settles between 5.2a_ in and 0.28 Hill radii of the binary. Here, a_ in is the semimajor axis of the binary D9. The inclination of the circumbinary disk follows that of the binary, which evolves due to the von Zeipel-Lidov-Kozai (vZLK) mechanism induced by Sgr A*. The mean eccentricity of the disk is approximately in antiphase with the eccentricity evolution of the binary. We find a vZLK timescale of T_ vZLK which is two orders of magnitude shorter than the value reported earlier. As a consequence, D9 has undergone multiple vZLK oscillations in its lifetime of 2.7 Myr. We find that the disk shows periodic bursts of mass loss on the vZLK timescale, suggesting that the mass loss itself is in part driven by the vZLK mechanism. The secular evolution observed in both the binary and the disk are consistent with theoretical predictions. We find the disk loses ∼7% ± 2% of its mass every vZLK cycle. If we extrapolate this mass loss, the disk will have 1% of its current mass left after another ∼4 Myr. D9 will then be ∼6.7 Myr old, which is on the same order as the current average age of S cluster members. The vZLK-driven mass loss could therefore explain the absence of Brγ emission from other S cluster members.

Abstract Among thousands of extragalactic γ -ray emitters, only a handful of distant ( z &gt; 3) sources are detected. Yet they are crucial probes, shedding light on the cosmic evolution of jets of active galactic nuclei and the initial phase of mass growth of supermassive black holes. Here, we report on a multiband study of the radio quasar B3 1239+376 at z = 3.82. By analyzing the Fermi Large Area Telescope data, a significant (globally 7.7 σ ) γ -ray source in its direction, with an estimated association probability of 0.91, is observed in a half-year period of 2025. The analysis also reveals the emergence of cospatial γ -ray residues in prior epochs. Moreover, the γ -ray and infrared light curves obtained from WISE and SPHEREx observations are likely correlated, as we observe that the emissions in both bands peak at the same time. The temporal coincidence establishes a firm association relationship between the γ -ray source and the quasar. Therefore, B3 1239+376 is proposed as the third-most-distant γ -ray detected blazar to date. Benefiting from the multiwavelength observations, broadband spectral energy distributions in different flux states are compiled and reproduced by the classic one-zone leptonic radiation model, to investigate the jet properties. Considering the recent brightening in γ rays, prompt follow-up observations are encouraged, especially radio interferometry observations that may catch the potential ejection of a new jet blob.

Abstract Nuclear star clusters (NSCs) surrounding supermassive black holes (SMBHs) are among the densest stellar environments in the Universe. In these environments, collisions can shape the stellar mass function and produce exotic stellar populations. In this work, we investigate how stellar collisions couple with stellar evolution in the inner parsec of an NSC. We simulate the evolution of a sample of 1000 1 M ⊙ stars embedded in a uniform cluster of dynamically relaxed 0.5 M ⊙ stars. Using COSMIC to evolve stellar properties in time, we track the mass, radius, and evolutionary state of the stars as they collide in the cluster. Our results show that most stars within 0.1 pc of the SMBH experience a collision while on the main sequence. However, outside of this distance, stars collide during the red giant phase, when the stellar radius increases dramatically. We find that the most common type of collision—main sequence or red giant—over the lifetime of the cluster depends on the steepness of the stellar cusp, which determines the spatial distribution of the stars in the cluster. These results show that stellar evolution plays a fundamental role in shaping the collisional history of stars in NSCs. Lastly, we consider whether the closest known stars to the Milky Way’s SMBH have experienced a collision. We estimate that several of the S-stars may experience a collision over their main-sequence lifetime, perhaps with implications for their observed youth and properties.