Search Results (191)

Globally self-gravitating accretion disks in active galactic nuclei (AGN) have been frequently discussed in the literature, but never observed. A few dozen megamasering accretion disks in AGN have been detected, which display a clear Keplerian rotation on scales of 0.1–1 pc, allowing us to estimate their masses within the sphere of influence (SoI) of the central supermassive black holes (SMBHs) to be smaller by more than a factor of 10, compared with the parent SMBH masses. Furthermore, the stellar components, deep inside the SoI, are dwarfed by the SMBH masses of $M_{•}\sim \mathrm{few}\times {10}^6$–$\mathrm{few}\times {10}^7{M}_{\odot }$. Theoretically, no limit exists on sizes and masses of gaseous disks in AGN, which in principle, can exceed masses of their central compact objects. We analyze instabilities which can operate in gaseous disks, i.e., fragmentation for a locally dominant self-gravity and spontaneous breaking of axial symmetry for the globally self-gravitating disks. We invoke the gas response to the latter instability which leads to gravitational collapse, leaving a negligible mass behind and dynamically stable remnants. Consequently, the characteristic timescale for globally self-gravitating disks to exist in AGN should not exceed few rotations, $t_{\varphi }\sim {10}^{3–4}$ yrs for $M_{•}\sim {10}^{6–8}{M}_{\odot }$. Disk rebuilding is expected to be ≳10⁷ yrs, meaning that probability of finding is ≲10⁻³, which explains their lack of detection. We conclude that observed sub-parsec disks in AGN, at least the Keplerian masering ones, can be remnants of globally self-gravitating accretion disks, and the instability timescale can be related to the duty cycle of AGN, $t_{\mathrm{duty}}~10t_{\varphi }~{10}^{4–5}$ yr. Full article

T Coronae Borealis (T CrB) is a symbiotic recurrent nova that is approaching its next thermonuclear eruption after a long super-active accretion state and a pre-eruption dip state. Flickering has been observed in T CrB for decades, but its amplitude in the red-optical TESS band and its dependence on accretion state have not yet been characterized using a homogeneous set of short-cadence space photometry. We analyze TESS Science Processing Operations Center light curves of T CrB obtained in Sectors 24, 25, 51, and 78. The primary measurements use the 120 s PDCSAP_FLUX products; agreement with independently detrended SAP_FLUX, 20 s products, and target-pixel checks demonstrates that the rapid signal is not created by Presearch Data Conditioning (PDC) processing or aperture contamination. After normalizing each light curve by its median flux, we remove slow sector-scale variability with a 0.5 d segment-wise smooth trend and measure the excess fractional rms variability, binned rms amplitudes, residual distributions, and power spectral densities. TESS detects millimagnitude-level stochastic variability in all four sectors. The total-light excess fractional rms values are ${0.273}_{-0.014}^{+0.013}$, ${0.276}_{-0.010}^{+0.010}$, ${0.318}_{-0.012}^{+0.013}$, and ${0.215}_{-0.017}^{+0.013}$ per cent in Sectors 24, 25, 51, and 78, respectively, equivalent to 2.96, 3.00, 3.45, and 2.33 mmag. The power spectral densities are red-noise-like, with slopes from $\alpha =-1.56\pm 0.09$ to $-1.19\pm 0.08$ over $5<f<120{\mathrm{d}}^{-1}$. The largest TESS-band flickering amplitude occurs in Sector 51, while the lowest occurs in Sector 78, observed in May 2024 after the end of the 2015–2023 super-active state and after the main pre-eruption dip. The persistence of flickering in Sector 78 shows that rapidly variable accretion continued, but the reduced amplitude indicates that the red-optical variable component was weaker, more diluted by the red giant, or geometrically altered. Because the TESS passband is dominated by the cool giant, the intrinsic fractional variability of the accretion component must be larger than the observed total-light values. Full article

As images of the supermassive black holes Messier 87* (M87*) and Sagittarius A* (Sgr A*) from the Event Horizon Telescope (EHT) grow in number, we gain a better understanding of the typical conditions of the near-horizon region of these objects, and slowly approach a converged time-average of the black hole image. In this article, we briefly review the signatures of black hole spin that manifest most apparently in these time-averaged images. We divide our discussion between coarse spatial features that are accessible with time averages from terrestrial very-long-baseline interferometry (VLBI) at 230 and 345 GHz, and fine spatial features which require either the extension of VLBI at these frequencies to space or the operation of global VLBI at much higher frequencies. We find that, while both coarse spatial features available from the ground and fine spatial features available only from space can both greatly inform spin, the primary difference is the degree of sensitivity to unknown astrophysical conditions, with photon ring-dominated observables benefitting from the exponential suppression of the details of the accretion disk. We conclude that spin measurements from resolved features of strong lensing are likely to provide sharp (∼±10%) spin measurements of both M87* and Sgr A* in the near future. Full article

A new mechanism for the formation of spectral–spatial distortions in cosmic microwave background radiation near primordial massive compact objects (such as primordial black holes) at redshifts from $z\sim 1000$ to ∼100 is proposed. After hydrogen recombination, the radiation from these objects leads to a significant increase in the population of hydrogen subordinate levels in their surrounding environment. Consequently, this allows for the observation of a Fraunhofer-like absorption spectrum in the cosmic microwave background. Such a distortion is formed due to the temperature difference between matter and relic radiation at the corresponding epoch. Ultimately, we should observe circular absorption or emission features around the objects with small angular sizes. These subordinate hydrogen lines currently lie in the radio wavelength range. Estimates indicate that the effect under consideration is accessible for the observations with planned large radiotelescopes. The possibility of the proposed mechanism lies in the ability of an object (e.g., accretion disk around black hole) to emit few-eV photons that populate the $n=2,3,4$ and higher levels of hydrogen, enabling the required excitation. Full article

We report a timing and spectral study of the 2024 outburst of the Be/X-ray binary pulsar 2S 1553-542 using NuSTAR and NICER observations. From the NuSTAR light curve, we measure a pulse period of $9.285022\pm 0.000001$ s. The energy-resolved pulse profiles are dominated by a single peak and show a wing-like structure most clearly in the 12–22 keV band. The pulsed fraction remains above 60% and increases with energy. The phase-averaged NuSTAR spectrum is described by an absorbed blackbody plus cutoff power-law continuum, together with an iron emission line and a cyclotron absorption feature. Using the cyclabs model, we obtain a cyclotron energy of $E_{\mathrm{cyc}}\simeq 24.1$ keV, corresponding to a magnetic field strength of $B\sim 3\times {10}^{12}$ G. Phase-resolved spectroscopy shows that the continuum and cyclotron-line parameters vary with pulse phase, and that the line becomes poorly constrained around the pulse-wing phase. We also searched the short NICER GTIs for transient mHz variability using wavelet analysis and a CEEMDAN-based Hilbert–Huang transform. Localized excesses near ∼10 mHz and ∼20 mHz are found, but the short exposures, COI effects, red-noise fluctuations, and the lack of a well-constrained Fourier peak limit their significance. We therefore treat them as candidate mHz variability rather than firm mHz QPO detections. Full article

The well-established anti-correlation between disk winds and relativistic jets in X-ray binaries is often interpreted in a scale-invariant black hole accretion context. If so, active galactic nuclei (AGN) should exhibit a direct mass-scaled analog. We test this prediction across FRII radio quasars, radio-quiet quasars, and jetted and non-jetted Narrow Line Seyfert 1 galaxies (NLS1) in spirals, among others. They exclude simple scale invariance. The highest-velocity winds occur exclusively in radio-quiet quasars, while powerful FRII quasars host systematically weaker winds despite equally large black hole masses. Jetted NLS1s show strong wind suppression consistent with X-ray binary behavior, whereas FRII quasars occupy a distinct regime in which jets and winds coexist. Black hole mass and spin magnitude alone cannot account for this dichotomy. We argue that the angular momentum direction of the disk relative to that of the black hole (aligned versus anti-aligned or co-rotation versus counter-rotation) is the critical parameter: secularly fueled spiral systems and most post-merger systems favor co-rotation, which is associated with compact ISCO radii, high radiative efficiency, strong winds, and jet suppression, while the counter-rotating subset of merger-influenced ellipticals can sustain powerful jets alongside moderate winds. Moreover, while spiral AGN and merger-driven radio-quiet quasars experience similar strong jet/wind anti-correlation, they cannot be treated as strict scaled analogs of X-ray binaries, which undergo rapid state transitions involving magnetic flux redistribution absent in AGN. At least two distinct wind–jet regimes therefore operate across the mass scale. We identify the details of this behavior across AGN subclasses. Full article

X-ray reflection spectroscopy provides one of the most effective electromagnetic routes to measuring the dimensionless spin parameter of accreting black holes. The method has produced spin constraints for both stellar-mass black holes in X-ray binaries and supermassive black holes in active galactic nuclei, and it is central to the science objectives of present and future X-ray telescopes. At the same time, this method is vulnerable to a set of coupled observational and modeling systematics: continuum-reflection degeneracy, insufficient passband, unresolved distant reflection or absorption, detector effects, source variability, accretion-state dependence, and assumptions built into the reflection model itself. This article synthesizes the talks and discussions held at the 2025 Wake Forest workshop Recent Progress on Black Hole Spin Measurements Across the Electromagnetic and Gravitational Spectra; motivated by them, we propose a practical quality-control framework for assessing whether a published reflection-based spin measurement should be treated as robust, provisional, or not assessable from the published information alone. We organize the problem around three pillars: detectability, meaning that the relativistic reflection signal is unambiguously present in the data; uniqueness, meaning that the relativistic component can be separated from the continuum, from distant reflection, absorption, and instrumental effects; and robustness, meaning that the inferred spin is stable against plausible changes in model assumptions, data selection, and accretion-state treatment. We then translate these principles into applicable criteria, a tiered quality-classification scheme, and a reporting checklist for future analyses. The quantitative calibration of each criterion requires a dedicated campaign of simulations over realistic scenarios, which we outline here and defer to a future publication. We aim to define a reproducible path toward a curated, community-maintained compilation of reliable spin constraints and to guide the implementation of reflection spectroscopy in the high-throughput, high-resolution era. Full article

Be/X-ray binaries constitute the largest and most diverse subgroup of neutron star high-mass X-ray binaries. These systems feature a rapidly rotating Be star surrounded by a circumstellar decretion disk that serves as the primary reservoir of accreted matter onto a strongly magnetized neutron star. While a few Be/X-ray binaries remain persistently active, the majority manifest as hard X-ray transient sources, becoming detectable only during X-ray outbursts. This review synthesizes current understanding of their rich phenomenology across optical and X-ray wavelengths, focusing on variability ocurring over timescales that span from seconds to years. Full article

We perform three-dimensional general relativistic magnetohydrodynamic (GRMHD) simulations of a near-maximally spinning black hole (spin parameter $a=0.998$) with varying initial magnetic field geometries, systematically exploring the parameter space connecting magnetically arrested disk (MAD), intermediate (INT), and standard and normal evolution (SANE) accretion states. The magnetic flux threading the black hole horizon emerges as the fundamental state variable controlling jet efficiency, flow magnetization, and radiative output across all three states. We introduce complementary diagnostics—broadband spectral energy distributions spanning radio through hard X-ray frequencies and time-resolved X-ray light curves—that together connect simulation dynamics directly to multiwavelength observables. The radiative output follows a clear MAD > INT > SANE hierarchy in time-averaged luminosity, mean X-ray emission, as well as variability. Furthermore, MAD exhibits the highest fractional variability through quasi-periodic magnetic flux eruption events, and INT and SANE show moderate variability driven by episodic reconnection and stochastic MRI turbulence, respectively. Scaling to GRS 1915+105, Cyg X-1, and HLX-1, we demonstrate that all twelve temporal classes of GRS 1915+105 map naturally onto our three magnetic states, Cyg X-1’s persistent hard state is reproduced by a sustained INT configuration, and HLX-1’s extreme luminosities arise through efficient Blandford–Znajek extraction in MAD states scaled to higher black hole mass. Full article

Recently, the coprecession of both the accretion disk and the jet formed following the tidal disruption event associated with the optical transient AT2020afhd, driven by a supermassive black hole of almost ten million solar masses, were independently measured in both the X and radio bands, respectively, showing a periodicity of nearly 20 days over about 300 days. An analytical model of the general relativistic gravitomagnetic Lense-Thirring precession of the effective orbit of a fictitious test particle revolving about a spinning primary can explain the observed precessional features. It yields allowed regions in the system’s parameter space which, as far as the hole’s dimensionless spin parameter is concerned, are essentially in agreement with those obtained in the literature with general relativistic magnetohydrodynamic simulations. The present analytical approach can be extended to include the precession due to the hole’s quadrupole mass moment as well. It breaks the degeneracy in the allowed regions occurring for negative and positive values of the spin parameter when only the Lense-Thirring effect is considered. The best estimate for the hole’s mass yields the range 0.185–0.215 for the dimensionless spin parameter. Using the same strategy with the gravitomagnetic frequency for an extended disk of finite size with a parameterized power-law mass density yields to distinct, generally non-overlapping allowed regions for each value of the power-law index adopted. Some of the assumptions on which this work is based are critically examined. Full article

The derivations presented in this paper suggest an intimate relationship between geometry and the electroweak sector at the Planck scale. A Lorentz-invariant maximally symmetric stochastically perturbed spacetime transformed to spherical coordinates reveals an emergent Schwarzschild metric, entirely a statistical structure of stochastic spacetime. Similarly, the transition from a maximally symmetric universe with a complex $SU\left(2\right)$ scalar doublet $\varphi$, comprising four independent real scalar fields with a zero vacuum expectation value (VEV), to spherical coordinates at the Planck scale reveals the spontaneously broken electroweak (EW) sector. Working in the unitarity gauge, the resulting EW potential can be simultaneously mapped in space at the Planck scale and across the EW sector. In space, the resulting EW potential includes a deep well within the Schwarzschild sphere and a shallow well just outside corresponding to an accretion disk. The same potential mapped in the EW space provides an entire family of possible sombrero hat potentials with fourth-order coupling specific to a point in space. At the minimum points of the potential in space, inside the Schwarzschild sphere and at the accretion disk, the $\lambda$ corresponding to the Standard Model (SM) fourth-order coupling is instead derived as $\frac{\lambda }{5}$. The factor of $\frac{1}{5}$ is a simple consequence of the conservation of the EW VEV and the fact that the SM formulation of the EW potential does not account for situations where the perturbations in $\varphi$ dominate. A more general formulation of the EW potential restores the SM quartic coupling and preserves $\lambda$ in space. An emergent Higgs field inside the Schwarzschild black hole is found to directly relate to the stochastic spacetime fields normalized by the Schwarzschild radius. The corresponding Higgs vacuum has both a ground and excited state and the possibility of both positive and negative vacuum entropy. Finally, the scalar-field VEV degeneracy in EW space of the metastable Higgs vacuum appears instead differentiated in space with possible probability, tunneling, and entropy implications. Full article

Black hole jets represent one of the most extreme manifestations of astrophysical processes, linking accretion physics, relativistic magnetohydrodynamics, and large-scale feedback in galaxies and clusters. Despite decades of observational and theoretical work, the mechanisms governing jet launching, collimation, and energy dissipation remain open questions. In this article, we discuss how upcoming facilities such as the Event Horizon Telescope (EHT), the Cherenkov Telescope Array (CTA), the Vera C. Rubin Observatory (LSST), and the Whole Earth Blazar Telescope (WEBT) will provide unprecedented constraints on jet dynamics, variability, and multi-wavelength signatures. Furthermore, we highlight theoretical challenges, including the role of magnetically arrested disks (MADs), plasma microphysics, and general relativistic magnetohydrodynamic (GRMHD) simulations in shaping our understanding of jet formation. By combining high-resolution imaging, time-domain surveys, and advanced simulations, the next decade promises transformative progress in unveiling the physics of black hole jets. Full article

Despite several efforts to investigate the accretion disk and torus, near-simultaneous broadband studies of the nuclear regions of radio-quiet AGNs remain lacking. NGC 4151, one of the closest and brightest Seyfert galaxies, provides an excellent laboratory for probing the circum-nuclear regions of AGNs. A detailed, near-simultaneous broadband spectral study of NGC 4151 is carried out during one of its historic minimum activity states, using archival data from the Ultraviolet (UV) to the Infrared (IR) regions. We used the radiative transfer code SKIRT to model the source and to constrain the properties of the torus. We found that the observed broadband spectral energy distribution is best explained by a two-torus geometry with a polar conical shell structure. Full article

Double-double radio galaxies (DDRGs) display inner and outer jets or lobes thought to result from intermittent accretion. Due to randomly triggered accretion events, the lifetime of the retriggered jet is not expected to have any connection to the time of quiescence between jets, yet we show that a correlation between the two quantities may exist, which we interpret as resulting from continued accretion through the quiescent jet phase. Despite continuous accretion, a jet is absent because its presence depends on a non-zero value of black hole spin, but accretion transitions the system from counter-rotation to corotation, and therefore through zero black hole spin where a jet cannot form. The time of jet quiescence depends on how long it takes to spin the black hole up again in corotation, which is longer for lower accretion rates. Once the black hole spin is large enough for a renewed jet, this inner jet will last longer the lower the accretion rate is. Hence, in a continuous accretion scenario, longer quiescent times tend to associate to longer inner jet times. In addition, DDRG jets are of FRII morphology which we show to result from the absence of a tilt in the accretion disk in the transition through zero black hole spin, ensuring the absence of an FRI jet in a way that connects with our understanding of X-shaped radio galaxies. Both correlated timescales as well as sameness in jet morphology offers evidence in favor of our picture. Full article

We investigate the thin accretion disk around Bardeen black hole (BH) surrounded by perfect fluid dark matter (PFDM), focusing on how the magnetic charge g and dark matter (DM) parameter b affect its radiative properties. The results show that increasing g slightly enhances the energy flux, radiation temperature, luminosity, and efficiency, while shifting the innermost stable circular orbit ($r_{\mathrm{isco}}$) inward. Additionally, the influence of b is found to be dominant, making it a key parameter in distinguishing PFDM-surrounded Bardeen BH from their Schwarzschild counterparts. Full article