Black Hole Research Articles

Another one (BH+OB pair) bites the dust

Most (or possibly all) massive stars reside in multiple systems. From stellar evolution models, numerous systems with an OB star coupled to a black hole would be expected to exist. There have been several claimed detections of such pairs in recent years and this is notably the case of Using high-quality photometry and spectroscopy in the optical range, we revisited the system. We also examined complementary X-ray observations to provide a broader view of the system properties. The light curves of clearly show eclipses, ruling out the black hole companion scenario. This does not mean that the system is not of interest. Indeed, the combined analysis of photometric and spectroscopic data indicates that the system most likely consists of a O8.5 giant star paired with a stripped-star companion with a mass of ∼4.5,M_⊙, a radius of ∼1,R_⊙, and a surface temperature of ∼50,kK. While several B+sdOB systems have been reported in the literature, this would be the first case of a Galactic system composed of an O star and a faint stripped star. In addition, the system appears brighter and harder than normal OB stars in the X-ray range, albeit less so than for X-ray binaries. The high-energy observations provide hints of phase-locked variations, as typically seen in colliding wind systems. As a post-interaction system actually represents a key case for probing binary evolution, even if it is not ultimately found to host a black hole.

Search and analysis of giant radio galaxies with associated nuclei (SAGAN). V. Study of giant double-double radio galaxies from LoTSS DR2

To test the hypothesis that megaparsec-scale giant radio galaxies (GRGs) experience multiple epochs of recurrent activity leading to their giant sizes and to understand the nature of double-double radio galaxies (DDRGs), we have built the largest sample of giant DDRGs from the LOFAR Two Metre Sky Survey (LoTSS) data release 2. This sample comprises 111 sources, including 76 newly identified DDRGs, with redshifts ranging from 0.06 to 1.6 and projected sizes between 0.7 Mpc and 3.3 Mpc. We conducted a detailed analysis to characterise their properties, including arm-length ratios, flux density ratios of pairs of lobes, and misalignment angles. These measurements allow us to study the symmetry parameters, which are influenced by the immediate and large-scale environments of DDRGs. Our study shows that based on the observed asymmetries of the inner lobes, the cocoons in which the inner lobes of DDRGs grow are often (approximately about 26%) asymmetrically contaminated with surrounding material from the external medium. Our analysis also reveals highly misaligned DDRGs, which could be due to environmental factors and/or changes in the supermassive black hole jet ejection axes. By studying the misalignment angles, we assess the stability of the jets in these systems in relation to their environment. For the first time, we systematically characterised the large-scale environments of DDRGs, identifying their association with dense galaxy clusters and revealing the influence of `cluster weather' on their morphologies. We have discovered a DDRG in a distant galaxy cluster at z∼,1.4. Our findings empirically confirm that dynamic cluster environments can induce significant misalignment in DDRGs, which aligns with previous simulation predictions and offers insights into how cluster weather shapes their morphology. Additionally, we have identified two gigahertz peaked-spectrum (GPS) candidates in the unresolved cores of the DDRGs, as well as one triple-double candidate, which, if confirmed, would be only the fifth known case. Overall, this study enhances our understanding of the life cycle of radio AGNs and underscores the critical role of the environment in shaping the properties and evolution of giant DDRGs.

Signature of Strange Star as the Central Engine of GRB 240529A

Abstract GRB 240529A is a long-duration gamma-ray burst (GRB) whose light curve of prompt emission is composed of a triple-episode structure, separated by quiescent gaps of tens to hundreds of seconds. More interestingly, its X-ray light curve of afterglow exhibits two plateau emissions, namely, an internal plateau emission that is smoothly connected with a ∼t −0.1 segment and followed by a ∼t −2 power-law decay. The three episodes in the prompt emission, together with two plateau emissions in X-ray, are unique in the Swift era. They are very difficult to explain with the standard internal/external shock model by invoking a black hole central engine. However, it could be consistent with the prediction of a supramassive magnetar as the central engine, the physical process of phase transition from a magnetar to a strange star, as well as the cooling and spin-down of the strange star. In this paper, we propose that the first- and second-episode emissions in the prompt gamma ray of GRB 240529A are from the jet emission of a massive star collapsing into a supramassive magnetar and the reactivity of the central engine, respectively. Then, the third-episode emission of the prompt is attributed to the phase transition from a magnetar to a strange star. Finally, the first and second plateau emissions of the X-ray afterglow are powered by the cooling and spin-down of the strange star, respectively. The observational data of each component of GRB 240529A are roughly coincident with the estimations of the above physical picture.

Revisiting the observation-theory confrontation in high-frequency QPOs: a new QPO in NGC 5506, intermediate mass black holes, and the crucial role of accretion state

Abstract The scale invariance of accretion processes (SIAP) is crucial for understanding the physical processes of black hole accretion systems at different scales. When applying this rule to high-frequency quasi-periodic oscillations (HFQPOs), there is an observation–theory confrontation in active galactic nuclei (AGNs). By compiling an updated X-ray HFQPO catalog, we found that the ultraluminous X-ray sources support the HFQPO models, similar to black hole X-ray binaries. More importantly, we identified two supermassive black hole (SMBH) sources (Sgr A* and NGC 1365) with possible advection-dominated accretion flow (ADAF) configurations that support existing HFQPO models, even though many AGNs still do not. Furthermore, we report a new HFQPO candidate in NGC 5506. This source exhibits an accretion state similar to that of Sgr A* and NGC 1365, and it also supports the HFQPO models. Our results are consistent with previous numerical simulations and suggest that the accretion state of HFQPOs in SMBHs may differ from that of stellar-mass black holes (SBHs). To reconcile the sources that do not support the models, either a global general-relativistic HFQPO model based on magnetohydrodynamics needs to be considered, or the HFQPOs in these sources may originate from entirely different physical processes. This discovery significantly extends the SIAP rule to a broader scale, confirming that the paradigm of accretion scale invariance remains consistent from SBHs to SMBHs.

Deep in the knotted black hole

We consider the transition rate of a freely falling Unruh-DeWitt detector, coupled linearly to a massless scalar quantum field prepared in the Hartle-Hawking-Israel state, as a probe of the interior of a black hole. Specifically, we consider the transition rate of a detector in the spinless Bañados-Teitelboim-Zanelli (BTZ) black hole as it freely falls toward and across the horizon and compare it to the corresponding situation for an RP2 geon. Both the BTZ black hole and its geon counterpart are quotients of AdS3 spacetime that are identical exterior to the horizon but have different interior topologies. We find outside the horizon that the rates are qualitatively similar, but with the amplitude in the geon spacetime larger than in the BTZ case. Once the detector crosses the horizon, there are notable distinctions characterized by different discontinuities in the temporal derivative of the response rate. These discontinuities can appear outside the horizon if the detector is switched on at a sufficiently early time, within the past white hole horizon. In general, the detector can act as an “early warning system” that both spots the black hole horizon and discerns its interior topology. Published by the American Physical Society 2025

Revisiting chronology protection conjecture in the Dyonic Kerr–Sen black hole spacetime

The chronology protection conjecture (CPC) was first introduced by Hawking after his semi-classical investigation of the behaviour of a spacetime with closed timelike curves (CTCs) in response to scalar perturbations. It is argued that there would be instabilities leading to amplification of the perturbation and finally causing collapse of the region with CTCs. In this work, we investigate the CPC by exactly solving the Klein–Gordon equation in the region inside the inner horizon of the non-extremal Dyonic Kerr–Sen (DKS) black hole, where closed timelike curves exist. Successfully find the exact radial solution, we apply the polynomial condition that turns into the rule of energy quantization. Among the quasi-resonance modes, only certain modes satisfy the boundary conditions of quasinormal modes (QNMs). QNMs in the region inside the inner horizon of the rotating black hole with nonzero energy have only positive imaginary parts which describe states that grow in time. The exponentially growing modes will backreact and deform the spacetime region where CTC exists, hence the CPC is proven to be valid in the non-extremal Dyonic Kerr–Sen black hole spacetime. Since the Dyonic Kerr–Sen black hole is the most general axisymmetric black hole solution of the string inspired Einstein–Maxwell-dilaton-axion (EMDA) theory, the semiclassical proof in this work is also valid for all simpler rotating black holes of the EMDA theory. The structure of the Dyonic KS spacetime distinctive from the Kerr–Newman counterpart is also explored.

Black Hole Singularity Resolution in Unimodular Gravity from Unitarity

We study the quantum dynamics of an interior planar anti–de Sitter black hole, requiring unitarity in the natural time coordinate conjugate to the cosmological “constant of motion” appearing in unimodular gravity. Both the classical singularity and the horizon are replaced by a nonsingular highly quantum region; semiclassical notions of spacetime evolution are only valid in an intermediate region. For the singularity, our results should be applicable to general black holes: unitarity in unimodular time always implies singularity resolution. Published by the American Physical Society 2025

Flares from plasmoids and current sheets around Sgr A*

The supermassive black hole Sgr A* at the center of our galaxy produces repeating near-infrared flares that are observed by ground- and space-based instruments. This activity has been simulated in the past with magnetically arrested disk models that include stable jet formations. We used a different approach, considering a standard and normal evolution (SANE) multi-loop model that lacks a stable jet structure. The main objective of this research is to identify regions that contain current sheets and high magnetic turbulence, and to subsequently generate a 2.2 μm light curve from nonthermal particles. These aims required the identification of areas that contain current sheets and high magnetic turbulence, and the averaging of the magnetization in the regions surrounding these areas. Subsequently, particle-in-cell fitting formulas were applied to determine the nonthermal particle distribution and to obtain the sought-after light curve. Additionally, we investigated the properties of the flares, in particular their evolution during flare events, and the similarity of flare characteristics between the generated and observed light curves. We employed 2D general relativistic magnetohydrodynamic simulation data from a SANE multi-loop model and introduced thermal radiation to generate a 230 GHz light curve. Physical variables were calibrated to align with the 230 GHz observations. We identified current sheets by analyzing toroidal currents, magnetization, plasma β, density, and dimensionless temperatures. We studied the evolution of current sheets during flare events and calculated higher-energy nonthermal light curves, focusing on the 2.2 μm near-infrared range. We obtain promising $2.2 μ$m light curves whose flare duration and spectral index behavior align well with observations. Our findings support the association of flares with particle acceleration and nonthermal emission in current sheet plasmoid chains and at the boundary of the disk inside the funnel above and below the central black hole.

Quantum radiation from round-trip flying mirrors

Erasing a black hole leaves spacetime flat, so light passing through the region before any star forms and after the black hole’s evaporation shows no time delay, just like a flying mirror that returns to its initial starting point. Quantum radiation from a round-trip flying mirror has not been solved despite the model’s mathematical simplicity and physical clarity. Here, we solve the particle creation from worldlines that asymptotically start and stop at the same spot, resulting in interesting spectra and symmetries, including the time dependence of thermal radiance associated with Bose-Einstein and Fermi-Dirac Bogoliubov coefficients. Fourier analysis, intrinsically linked to the Bogoliubov mechanism, shows that a thermal Bogoliubov distribution does not describe the spin-statistics of the quantum field. Published by the American Physical Society 2025

Mapping inspiral-merger-ringdown waveforms of binary black holes from black hole perturbation waveforms by machine learning

Mapping inspiral-merger-ringdown waveforms of binary black holes from black hole perturbation waveforms by machine learning

Revisiting black holes surrounded by cloud and fluid of strings in general relativity

Revisiting black holes surrounded by cloud and fluid of strings in general relativity

An optical perspective on early-stage active galactic nuclei with extreme radio flares

Over the last decade of active galactic nucleus (AGN) monitoring programs, the Metsähovi Radio Observatory has made multiple detections of seven powerful flaring narrow-line Seyfert 1 (NLS1) galaxies at 37 GHz. Several hypotheses have been proposed, but understanding this unique phenomenon is still far away. To look at the case from a different point of view, we performed an emission line analysis of the optical spectra, with the aim of identifying similarities among the sources, which in turn can possibly be tied with radio behavior. Our data were obtained with the Gran Telescopio Canarias. The results we obtained show that six out of the seven sources have typical properties for the NLS1 class, and one of them is an intermediate Seyfert galaxy. We found on average black hole masses above the median value for the class (> 10^7 M_⊙), and a strong Fe II emission, which could be a proxy for an intense ongoing accretion activity. Although interesting, the characteristics we found are not unusual for this kind of AGN: the optical spectra of our sources do not relate with their unique radio properties. Therefore, further multi-wavelength studies will be necessary to narrow the field of hypotheses for this peculiar phenomenon.

GA-NIFS: High number of dual active galactic nuclei at z∼ 3

Merger events can trigger gas accretion onto supermassive black holes (SMBHs) located at the centre of galaxies and form close pairs of active galactic nuclei (AGNs). The fraction of AGNs in pairs offers critical insights into the dynamics of galaxy interactions, SMBH growth, and their co-evolution with host galaxies. However, the identification of dual AGNs is difficult, as it requires high-quality spatial and spectral data; hence, very few pairs have been found in the distant Universe so far. This study is aimed at providing a first observational estimate of the fraction of dual AGNs at $2 < z < 6$ by analysing a sample of 16 AGNs observed with the JWST Near-InfraRed Spectrograph (NIRSpec) in integral field mode, as part of the GA-NIFS survey. For two AGNs in our sample, we also incorporated archival VLT/MUSE data to expand the search area. We searched for nearby companion galaxies and emission-line sources within the ∼ 20 20 kpc field of view of the NIRSpec data cubes, extending up to ∼50 kpc using the MUSE data cubes. We analysed the spectra of such emitters to determine their physical and kinematic properties. We report the serendipitous discovery of a triple AGN system and four dual AGNs (two of which had been considered as candidates), with projected separations in the range 3--28 kpc. The results of this study more than double the number of known multiple AGNs at z > 3 at these separations. Their AGN classification is mainly based on standard optical emission line flux ratios, as observed with JWST/NIRSpec, and complemented with additional multi-wavelength diagnostics. The identification of these 3-5 multiple AGNs out of the 16 AGN systems in the GA-NIFS survey (i.e. ∼ 20--30%) suggests they might be more common than previously thought from other observational campaigns. Moreover, our inferred fraction of dual AGN moderately exceeds predictions from cosmological simulations that mimic our observational criteria (∼ 10%). This work highlights the exceptional capabilities of NIRSpec for detecting distant dual AGNs, prompting new investigations to constrain their fraction across cosmic time.

Topologically charged BPS microstates in AdS3/CFT2

In the standard N = (4, 4) AdS3/CFT2 with symN (T4), as well as the N = (2, 2) Datta-Eberhardt-Gaberdiel variant with symN (T4/ℤ2), supersymmetric index techniques have not been applied so far to the CFT states with target-space momentum or winding. We clarify that the difficulty lies in a central extension of the SUSY algebra in the momentum and winding sectors, analogous to the central extension on the Coulomb branch of 4d N = 2 gauge theories. We define modified helicity-trace indices tailored to the momentum and winding sectors, and use them for microstate counting of the corresponding bulk black holes. In the N = (4, 4) case we reproduce the microstate matching of Larsen and Martinec. In the N = (2, 2) case we resolve a previous mismatch with the Bekenstein-Hawking formula encountered in the topologically trivial sector by going to certain winding sectors.

JWST + ALMA ubiquitously discover companion systems within <18 kpc around four z≈3.5 luminous radio-loud AGN

Mergers play important roles in galaxy evolution at and beyond cosmic noon (z∼3). They have been found to be a trigger of active galactic nuclei (AGN) activity and a process for growing stellar mass and black hole mass. High-z radio galaxies (HzRGs=type-2 radio-loud AGN) are among the most massive galaxies known, and they reside in dense environments on scales of tens of kiloparsecs to Megaparsecs. We present the first search for kiloparsec-scale companions using matched 0.2 resolution ALMA and JWST/NIRSpec integral field unit data in a sample of four z∼3.5 HzRGs with many supporting datasets. We discovered a total of ∼12 companion systems within lesssim18,kpc across all four HzRG fields using two independent detection methods: peculiar O iii $4959,5007$ kinematics offset from the main (systemic) ionized gas component and C ii μ m$ emitters. We examined the velocity fields of these companions and find evidence of disk rotation along with more complex motions. We estimate the dynamical masses of these nearby systems to be dyn ∼10^ ⊙ which may indicate a minor merger scenario. Our results indicate that these companions may be the trigger of the powerful radio-loud AGN. We discuss the roles of the discovered companion systems in galaxy evolution for these powerful jetted AGN and indicate that they may impede jet launch and deflect the jet.

Tension of the toroidal magnetic field in reconnection plasmoids and relativistic jets

The toroidal magnetic field is a key ingredient of relativistic jets launched by certain accreting astrophysical black holes, and of plasmoids emerging from the tearing instability during magnetic reconnection, which is a candidate dissipation mechanism in jets. Tension of the toroidal field is an anisotropic force that can compress local energy and momentum densities. We investigate this effect in plasmoids produced during relativistic reconnection initiated from a Harris layer by means of kinetic particle-in-cell numerical simulations, varying the system size (including 3D cases), magnetisation, or guide field. We find that: (1) plasmoid cores are dominated by plasma energy density for guide fields up to B_z ∼ B_0; (2) relaxed `monster' plasmoids compress plasma energy density only modestly (by a factor of ∼ 3 above the initial level for the drifting particle population); (3) energy density compressions by factors ≳ 10 are achieved during plasmoid mergers, especially with the emergence of secondary plasmoids. This kinetic-scale effect can be combined with a global focusing of the jet Poynting flux along the quasi-cylindrical bunched spine (a proposed jet layer adjacent to the cylindrical core) due to poloidal line bunching (a prolonged effect of tension in the jet toroidal field) to enhance the luminosity of rapid radiation flares from blazars. The case of M87 as a misaligned blazar is discussed.

Strong Gravitational Lensing and Shadows by Quantum Schwarzschild Black Hole in Homogeneous Plasma

Strong Gravitational Lensing and Shadows by Quantum Schwarzschild Black Hole in Homogeneous Plasma

Tripling the Census of Dwarf AGN Candidates Using DESI Early Data

Abstract Using early data from the Dark Energy Spectroscopic Instrument (DESI) survey, we search for active galactic nuclei (AGN) signatures in 410,757 line-emitting galaxies. By employing the BPT emission-line ratio diagnostic diagram, we identify AGNs in 75,928/296,261 (≈25.6%) high-mass ( log ( M ⋆ / M ⊙ ) > 9.5) and 2444/114,496 (≈2.1%) dwarf ( log ( M ⋆ / M ⊙ ) ≤ 9.5) galaxies. Of these AGN candidates, 4181 sources exhibit a broad Hα component, allowing us to estimate their BH masses via virial techniques. This study more than triples the census of dwarf AGNs and doubles the number of intermediate-mass black hole (M BH ≤ 106 M ⊙) candidates, spanning a broad discovery space in stellar mass (7 < log ( M ⋆ / M ⊙ ) < 12) and redshift (0.001 <z < 0.45). The observed AGN fraction in dwarf galaxies (≈2.1%) is nearly four times higher than prior estimates, primarily due to DESI’s smaller fiber size, which enables the detection of lower-luminosity dwarf AGN candidates. We also extend the M BH–M ⋆ scaling relation down to log ( M ⋆ / M ⊙ ) ≈ 8.5 and log ( M BH / M ⊙ ) ≈ 4.4, with our results aligning well with previous low-redshift studies. The large statistical sample of dwarf AGN candidates from current and future DESI releases will be invaluable for enhancing our understanding of galaxy evolution at the low-mass end of the galaxy mass function.

BPS fivebrane stars. Part III. Effective actions

An effective action for NS5-branes coupled to supergravity is used to derive the full 10d form of horizon-free BPS solutions of fivebranes carrying momentum waves, including both transverse scalar and internal gauge excitations of the branes. When internal modes are highly excited, we find solutions that plausibly mediate the transition between the Coulomb phase of NS5-branes and the black hole phase. We also compute the two-point functions of fivebrane density fluctuations and of gravitons absorbed by the branes. Finally, we begin an exploration of near-BPS perturbations of the fivebrane ensemble, and propose the use of the brane+bulk effective action as a tool to explore the black hole phase, even in the AdS decoupling limit.

Regular Schwarzschild black holes and cosmological models

Regular Schwarzschild black holes and cosmological models