Higher Spin Black Holes Research Articles

Chaotic magnetic disconnections trigger flux eruptions in accretion flows channeled onto magnetically saturated Kerr black holes

Magnetized accretion flow onto a black hole (BH) may lead to the accumulation of poloidal magnetic flux across its horizon, which for high BH spin can power far-reaching relativistic jets. The BH magnetic flux is subject to a saturation mechanism by means of magnetic flux eruptions involving relativistic magnetic reconnection. Such accretion flows have been described as magnetically arrested disks (MAD) or magnetically choked accretion flows (MCAF). The main goal of this work is to describe the onset of relativistic reconnection and initial development of magnetic flux eruption in accretion flow onto magnetically saturated BHs. We analyzed the results of 3D general relativistic ideal magnetohydrodynamic (GRMHD) numerical simulations in the Kerr metric, starting from weakly magnetized geometrically thick tori rotating either prograde or retrograde. We integrate d large samples of magnetic field lines in order to probe magnetic connectivity with the BH horizon. The boundary between magnetically connected and disconnected domains coincides roughly with enthalpy equipartition. The geometrically constricted innermost part of the disconnected domain develops a rigid structure of magnetic field lines -- rotating slowly and insensitive to the BH spin orientation. The typical shape of innermost disconnected lines is a double spiral converging to a sharp inner tip anchored at the single equatorial current layer. The foot points of magnetic flux eruptions are found to zip around the BH along with other azimuthal patterns. Magnetic flux eruptions from magnetically saturated accreting BHs can be triggered by minor density gaps in the disconnected domain, resulting from the chaotic disconnection of plasma-depleted magnetospheric lines. Accretion flow is effectively channeled along the disconnected lines toward the current layer, and further toward the BH by turbulent cross-field diffusion. Rotation of flux eruption foot points may contribute to the variability of BH crescent images.

An upper limit on the spins of merging binary black holes formed through isolated binary evolution

As the sensitivity of ground-based gravitational wave detectors progressively increases, observations of black hole mergers will provide us with the joint distribution of their masses and spins. This will be a critical benchmark to validate different formation scenarios. Merging binary black holes formed through the evolution of isolated binary systems require both components to be stripped of their hydrogen envelopes before core-collapse. The rotation rates of such stripped stars are constrained by the critical rotation limit at their surface, including its deviation from the Keplerian value owing to the outward force provided by radiation. This sets a restriction on their angular momentum content at core-collapse. We aim to determine if this restriction plays a role in the spins of binary black hole mergers. We used detailed calculations of stripped stars with the MESA code at low metallicities ($Z=Z_ $Z_ and $Z_ to determine the dimensionless spins of black holes produced by critically rotating stellar progenitors. To study how such progenitors can arise, we considered their formation through chemically homogeneous evolution (CHE) in binary stars. We used a semi-analytical model to study the physical processes that determine the final angular momentum of CHE binaries, and compared our results against available population synthesis models that rely on detailed binary evolution calculations. We find that above black hole masses of $ 25M_ the dimensionless spin parameter of critically rotating stripped stars ($a=Jc/(GM^2)$) is below unity. This results in an exclusion region at high chirp masses and effective spins that cannot be populated by isolated binary evolution. CHE can produce binaries where both black holes hit this limit, producing a pileup at the boundary of the excluded region. High-spin black holes arise from very low-metallicity CHE systems with short delay times, which merge at higher redshifts. On the other hand, the contribution of CHE to merging binary black holes detected in the third observing run of the LVK collaboration is expected to be dominated by systems with low spins ($ eff <0.5$) that merge near redshift zero. Owing to its higher projected sensitivity and runtime, the fourth observing run of the LVK collaboration can potentially place constraints on the high-spin population and the existence of a limit set by critical rotation.

Jets, accretion and spin in supermassive black holes

Abstract The theoretical model suggests that relativistic jets of AGN rely on the black hole spin and/or accretion. We study the relationship between jet, accretion, and spin using supermassive black hole samples with reliable spin of black holes.
Our results are as follows: (1) There is a weak correlation between radio luminosity and the spin of black hole for our sample, which may imply that the jet of the supermassive black hole in our sample depends on the other physical parameters besides black hole spins, such as accretion disk luminosity. (2) The jet power of a supermassive black hole can be explained by the hybrid model with magnetic field of corona. (3) There is a significant correlation between radio-loudness and black hole spin for our sample. These sources with high radio-loudness tend to have high black hole spins. These results provide observational evidence that the black hole spin may explain the bimodal phenomena of radio-loud and radio-quiet AGN.

Accretion Properties of Soft X-Ray Transient XTE J1856+053 during Its 2023 Outburst

Soft X-ray transients (SXTs) are a subclass of the low-mass X-ray binaries that occasionally show a sudden rise in their soft X-ray luminosity; otherwise, they remain in an extremely faint state. We investigate the accretion properties of the SXT XTE J1856+053 during its 2023 outburst obtained by NICER and NuSTAR data in July. We present detailed results on the timing and spectral analysis of the X-ray emission during the outburst. The power spectral density shows no quasi-periodic oscillation features. The source’s spectrum on July 19 can be well fitted with a multicolor blackbody component, a power-law component, and a reflection component with a broadened iron emission line. NICER spectra can be well fitted by considering a combination of a blackbody and a power law. The source exhibits a transition within just 5 days from a soft state to an intermediate state during the outburst decline phase. The inner accretion disk has a low inclination angle (∼18°). The spectral analysis also suggests a high-spin (a > 0.9) black hole as the central accreting object.

Photon emissions from Kerr equatorial geodesic orbits

We consider the light emitters moving freely along the geodesics on the equatorial plane near a Kerr black hole and study the observability of these emitters. To do so, we assume these emitters emit photons isotropically and monochromatically, and we compute the photon escaping probability (PEP) and the maximum observable blueshift (MOB) of the photons that reach infinity. We obtain numerical results of PEP and MOB for the emitters along various geodesic orbits, which exhibit distinct features for the trajectories of different classes. In particular, we find that the plunging emitters could have considerable observability even in the near-horizon region. This interesting observational feature becomes more significant for the high-energy emitters near a high-spin black hole. As the radiatively-inefficient accretion flow may consist of plunging emitters, the present work could be of great relevance to the astrophysical observations.

Modeling the inner part of the jet in M87: Confronting jet morphology with theory.

The formation of jets in black hole accretion systems is a long-standing problem. It has been proposed that a jet can be formed by extracting the rotation energy of the black hole ("BZ-jet") or the accretion flow ("disk-jet"). While both models can produce collimated relativistic outflows, neither has successfully explained the observed jet morphology. By using general relativistic magnetohydrodynamic simulations and considering nonthermal electrons accelerated by magnetic reconnection that is likely driven by magnetic eruption in the underlying accretion flow, we obtain images by radiative transfer calculations and compared them to millimeter observations of the jet in M87. We find that the BZ-jet originating from a magnetically arrested disk around a high-spin black hole can well reproduce the jet morphology, including its width and limb-brightening feature.

Research on the uncertainties of black hole spin measurement

Black hole is an important object and research object in astronomy and spin is one of the three physical quantities used to describe them. Its vital to get the spin parameter of a black hole as accurate as possible. Recently, researchers have used many methods to measure the spin parameter and two of them are most commonly used, the continuum-fitting method and the reflection-fitting method. Its difficult to avoid errors in the measurement of the two methods, but we can use various methods to minimize the error in the measurement. In this paper, we try to figure out using the two methods in measuring what kind of black holes spin can we reduce errors. We consider both the systematic error caused by model assumptions and the accidental error caused by dynamical parameter. Finally, we conclude that both the two methods can only measure black holes with certain accretion rate between 0.01 - 0.3. The continuum-fitting method can reduce errors in measuring high-spin black hole with small viscosity of the accretion disk. The reflection-fitting method can reduce errors in measuring high-spin/ low corona-height black hole.

The SOUX AGN sample: optical/UV/X-ray SEDs and the nature of the disc

ABSTRACT We use the SOUX sample of ∼700 active galactic nucleus (AGN) to form average optical-ultraviolet (UV)-X-rays spectral energy distributions (SEDs) on a two-dimensional (2D) grid of MBH and L2500. We compare these with the predictions of a new AGN SED model, qsosed, which includes prescriptions for both hot and warm Comptonization regions as well as an outer standard disc. This predicts the overall SED fairly well for 7.5 < log(MBH/M⊙) < 9.0 over a wide range in L/LEdd, but at higher masses the outer disc spectra in the model are far too cool to match the data. We create optical-UV composites from the entire Sloan Digital Sky Survey sample and use these to show that the mismatch is due to there being no significant change in spectral shape of the optical-UV continuum across several decades of MBH at constant luminosity. We show for the first time that this cannot be matched by standard disc models with high black hole spin. These apparently fit, but are not self-consistent as they do not include the General Relativistic effects for the emission to reach the observer. At high spin, increased gravitational redshift compensates for almost all of the higher temperature emission from the smaller inner disc radii. The data do not match the predictions made by any current accretion flow model. Either the disc is completely covered by a warm Comptonization layer whose properties change systematically with L/LEdd, or the accretion flow structure is fundamentally different to that of the standard disc models.

The Hard-to-soft Transition of GX 339–4 as Seen by Insight–HXMT

We present an analysis of the relativistic reflection spectra of GX 339–4 during the hard-to-soft transition of its 2021 outburst observed by Insight–HXMT. The strong relativistic reflection signatures in the data suggest a high black hole spin (a * > 0.86) and an intermediate disk inclination angle (i ≈ 35°–43°) of the system. The transition is accompanied by an increasing temperature of the disk and a softening of the corona emission, while the inner disk radius remains stable. Assuming a lamppost geometry, the corona height is also found to stay close to the black hole across the state transition. If we include the Comptonization of the reflection spectrum, the scattering fraction parameter is found to decrease during the state transition. We also perform an analysis with a reflection model designed for hot accretion disks of stellar mass black holes where the surface of the innermost accretion disk is illuminated by emission from the corona and the thermal disk below. Our results support the scenario in which the state transition is associated with variations in the corona properties.

The Spin of a Newborn Black Hole: Swift J1728.9-3613

The origin and distribution of stellar-mass black hole spins are a rare window into the progenitor stars and supernova events that create them. Swift J1728.9-3613 is an X-ray binary, likely associated with the supernova remnant (SNR) G351.9-0.9. An NuSTAR X-ray spectrum of this source during its 2019 outburst reveals reflection from an accretion disk extending to the innermost stable circular orbit. Modeling of the relativistic Doppler shifts and gravitational redshifts imprinted on the spectrum measures a dimensionless spin parameter of a = 0.86 ± 0.02 (1σ confidence), a small inclination angle of the inner accretion disk θ < 10°, and a subsolar iron abundance in the disk A Fe < 0.84. This high spin value rules out a neutron star primary at the 5σ level of confidence. If the black hole is located in a still visible SNR, it must be young. Therefore, we place a lower limit on the natal black hole spin of a > 0.82, concluding that the black hole must have formed with a high spin. This demonstrates that black hole formation channels that leave an SNR, and those that do not (e.g., Cyg X-1), can both lead to high natal spin with no requirement for subsequent accretion within the binary system. Emerging disparities between the population of high-spin black holes in X-ray binaries and the low-spin black holes that merge in gravitational wave events may therefore be explained in terms of different stellar conditions prior to collapse, rather than different environmental factors after formation.

Rimmed and rippled accretion disc models to explain AGN continuum lags

ABSTRACT We propose a solution to the problem of accretion disc sizes in active galactic nuclei being larger when measured by reverberation mapping than predicted by theory. Considering the disc’s exposed-surface thickness profile H(r), our solution invokes a steep rim or rippled structures irradiated by the central lamp-post. We model the continuum lags and the faint and bright disc spectral energy distribution (SED) in the best-studied case NGC 5548 (black hole mass $M_\bullet =7\times 10^7\, \mathrm{M}_\odot$, disc inclination i = 45°). With the lamp-post off, the faint-disc SED fixes a low accretion rate $\dot{M}\simeq 0.0014~\mathrm{M}_\odot \, {\rm yr}^{-1}$ and high prograde black hole spin a• ≃ 0.93, for which $r_{\rm in}=2\, G\, M_\bullet /c^2$ and $L_{\rm disc}=0.25\, \dot{M}\, c^2$. The bright-disc SED then requires a lamp-post luminosity ${L_{\rm LP}}\simeq 5\, \dot{M}\, c^2/(1-A)$ for disc albedo A. Reprocessing on the thin disc with T ∝ r−3/4 gives time lags τ ∝ λ4/3 but three times smaller than observed. Introducing a steep H(r) rim, or multiple crests, near r ∼ 5 light days, reprocessing on the steep centre-facing slope increases temperatures from ∼1500 to ∼6000 K, and this increases optical lags to match the lag data. Most of the disc surface maintains the cooler T ∝ r−3/4 profile that matches the SED. The bright lamp-post may be powered by magnetic links tapping the black hole spin. The steep rim occurs near the disc’s dust sublimation radius as in the ‘failed disc wind model for broad-line clouds’. Lens–Thirring torques aligning the disc and black hole spin may also raise a warp and associated waves. In both scenarios, the small density scale height implied by the inferred value of H(r) suggests possible marginal gravitational instability in the disc.

Mechanisms for high spin in black-hole neutron-star binaries and kilonova emission: inheritance and accretion

ABSTRACT A black-hole neutron-star binary merger can lead to an electromagnetic counterpart called a kilonova if the neutron star is disrupted prior to merger. The observability of a kilonova depends on the amount of neutron star ejecta, which is sensitive to the aligned component of the black hole spin. We explore the dependence of the ejected mass on two main mechanisms that provide high black hole spin in isolated stellar binaries. When the black hole inherits a high spin from a Wolf–Rayet star that was born with least $\sim 10{{\ \rm per\ cent}}$ of its breakup spin under weak stellar core-envelope coupling, relevant for all formation pathways, the median of the ejected mass is ≳10−2 M⊙. Though only possible for certain formation pathways, similar ejected mass results when the black hole accretes $\gtrsim 20{{\ \rm per\ cent}}$ of its companion’s envelope to gain a high spin. Together, these signatures suggest that a population analysis of black-hole neutron-star binary mergers with observed kilonovae may help distinguish between mechanisms for spin and possible formation pathways. We show that these kilonovae will be difficult to detect with current capabilities, but that future facilities, such as the Vera Rubin Observatory, can do so even if the aligned dimensionless spin of the black hole is as low as ∼0.2. Our model predicts kilonovae as bright as Mi ∼ −14.5 for an aligned black hole spin of ∼0.9 and mass ratio Q = 3.6.

The jet formation mechanism of gamma-ray narrow-line Seyfert 1 galaxies

ABSTRACT Under a coronal magnetic field, we estimate the maximal jet power of the Blandford–Znajek (BZ) mechanism, Blandford–Payne (BP) mechanism, and hybrid model. The jet power of the BZ and hybrid model mechanisms depends on the spin of the black hole, while the jet power of the BP mechanism does not depend on the spin of the black hole. At high black hole spin, the jet power of the hybrid model is greater than that of the BZ and BP mechanisms. We find that the jet power of almost all gamma-ray narrow-line Seyfert 1 galaxies (γNLS1s) can be explained by the hybrid model. However, one source with jet power ∼0.1–1 Eddington luminosity cannot be explained by the hybrid model. We suggest that a magnetic field dragged inward by the accretion disc with magnetization-driven outflows may accelerate the jets in this γNLS1.

An elliptical accretion disk following the tidal disruption event AT 2020zso

Aims. The modelling of spectroscopic observations of tidal disruption events (TDEs) to date suggests that the newly formed accretion disks are mostly quasi-circular. In this work we study the transient event AT 2020zso, hosted by an active galactic nucleus (AGN; as inferred from narrow emission line diagnostics), with the aim of characterising the properties of its newly formed accretion flow. Methods. We classify AT 2020zso as a TDE based on the blackbody evolution inferred from UV/optical photometric observations and spectral line content and evolution. We identify transient, double-peaked Bowen (N III), He I, He II, and Hα emission lines. We model medium-resolution optical spectroscopy of the He II (after careful de-blending of the N III contribution) and Hα lines during the rise, peak, and early decline of the light curve using relativistic, elliptical accretion disk models. Results. We find that the spectral evolution before the peak can be explained by optical depth effects consistent with an outflowing, optically thick Eddington envelope. Around the peak, the envelope reaches its maximum extent (approximately 1015 cm, or ∼3000–6000 gravitational radii for an inferred black hole mass of 5−10 × 105 M⊙) and becomes optically thin. The Hα and He II emission lines at and after the peak can be reproduced with a highly inclined (i = 85 ± 5 degrees), highly elliptical (e = 0.97 ± 0.01), and relatively compact (Rin = several 100 Rg and Rout = several 1000 Rg) accretion disk. Conclusions. Overall, the line profiles suggest a highly elliptical geometry for the new accretion flow, consistent with theoretical expectations of newly formed TDE disks. We quantitatively confirm, for the first time, the high inclination nature of a Bowen (and X-ray dim) TDE, consistent with the unification picture of TDEs, where the inclination largely determines the observational appearance. Rapid line profile variations rule out the binary supermassive black hole hypothesis as the origin of the eccentricity; these results thus provide a direct link between a TDE in an AGN and the eccentric accretion disk. We illustrate for the first time how optical spectroscopy can be used to constrain the black hole spin, through (the lack of) disk precession signatures (changes in inferred inclination). We constrain the disk alignment timescale to &gt; 15 days in AT2020zso, which rules out high black hole spin values (a &lt; 0.8) for MBH ∼ 106 M⊙ and disk viscosity α ≳ 0.1.

Solutions in Nonlinear Electrodynamics and their double copy regular black holes

We study solutions in non-linear electrodynamics (NED) and establish several general results. We show, that the SO(2) electric-magnetic duality symmetry is restrictive enough to allow for reconstruction of the NED Lagrangian from the spherically-symmetric electrostatic (Coulomb-like) solution — although there are infinitely many different NED theories admitting a given solution, there exists a unique SO(2) invariant one among them under a simple analyticity assumption (that leaves out some interesting physical theories). We introduce a general algorithm for constructing new SO(2) invariant NED theories in the conventional approach, where only a few examples are available. We also show how to derive the Lagrangian of the SO(2) invariant theory admitting a given electrostatic solution. We further show on a simple example that some NED theories may require sources (particles) of finite (non-zero) size. Such a non-zero size source not only regularizes the infinite energy of the point charge but also satisfies the condition of regularity, that the electric field is zero at the origin. The latter condition was identified earlier as necessary and sufficient for the NED solution to generate a regular black hole via so-called double copy construction and is also satisfied by solitons. We propose a large class of solitonic NED solutions that give rise to regular black holes via double copy construction and contain solutions of Maxwell and Born-Infeld as different limits. This class of NED solutions acquires two new properties in the limit where the corresponding regular black hole’s asymptotics becomes Minkowski: it gives rise to regular higher-spin black holes via generalization of double copy — “higher-copy” construction, and for very short distances changes the sign of the force becoming repulsive/attractive for opposite/similar signs of charges.

MIGHTEE: the nature of the radio-loud AGN population

ABSTRACT We study the nature of the faint radio source population detected in the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Early Science data in the COSMOS field, focusing on the properties of the radio-loud active galactic nuclei (AGNs). Using the extensive multiwavelength data available in the field, we are able to classify 88 per cent of the 5223 radio sources in the field with host galaxy identifications as AGNs (35 per cent) or star-forming galaxies (54 per cent). We select a sample of radio-loud AGNs with redshifts out to z ∼ 6 and radio luminosities 1020 &amp;lt; L1.4 GHz/W Hz−1 &amp;lt; 1027 and classify them as high-excitation and low-excitation radio galaxies (HERGs and LERGs). The classification catalogue is released with this work. We find no significant difference in the host galaxy properties of the HERGs and LERGs in our sample. In contrast to previous work, we find that the HERGs and LERGs have very similar Eddington-scaled accretion rates; in particular we identify a population of very slowly accreting AGNs that are formally classified as HERGs at these low radio luminosities, where separating into HERGs and LERGs possibly becomes redundant. We investigate how black hole mass affects jet power, and find that a black hole mass ≳ 107.8 M⊙ is required to power a jet with mechanical power greater than the radiative luminosity of the AGN (Lmech/Lbol &amp;gt; 1). We discuss that both a high black hole mass and black hole spin may be necessary to launch and sustain a dominant radio jet.

Efficient simulations of high-spin black holes with a new gauge

We present a new choice of initial data for binary black hole simulations that significantly improves the efficiency of high-spin simulations. We use spherical Kerr-Schild coordinates, where the horizon of a rotating black hole is spherical, for each black hole. The superposed spherical Kerr-Schild initial data reduce the runtime by a factor of 2 compared to standard superposed Kerr-Schild for an intermediate resolution spin-0.99 binary-black-hole simulation. We also explore the possibility of delaying the transition from the initial data gauge to the evolution gauge, which produces an additional speed-up of 1.3.

Photon emission from circular equatorial Kerr orbiters

We consider monochromatic and isotropic photon emission from circular equatorial Kerr orbiters. We derive analytic expressions for the photon escape probability and the redshift-dependent total flux collected on the celestial sphere as a function of emission radius and black hole parameters. These calculations crucially involve the critical curve delineating the region of photon escape from that of photon capture in each emitter's sky. This curve generalizes to finite orbital radius the usual Kerr critical curve and displays interesting features in the limit of high spin, which we investigate by developing a perturbative expansion about extremality. Although the innermost stable circular orbit appears to approach the event horizon for very rapidly spinning black holes, we find in this regime that the photon escape probability tends to $5/12+1/(\sqrt{5}\pi)\arctan\sqrt{5/3}\approx54.65\%$. We also obtain a simple formula for the flux distribution received on the celestial sphere, which is nonzero. This confirms that the near-horizon geometry of a high-spin black hole is in principle observable. These results require us to introduce a novel type of near-horizon double-scaling limit. We explain the dip observed in the total flux at infinity as an imprint of the black hole: the black hole "bite".

Optical follow-up of the neutron star–black hole mergers S200105ae and S200115j

LIGO and Virgo’s third observing run revealed the first neutron star–black hole (NSBH) merger candidates in gravitational waves. These events are predicted to synthesize r-process elements1,2 creating optical/near-infrared ‘kilonova’ emission. The joint gravitational wave and electromagnetic detection of an NSBH merger could be used to constrain the equation of state of dense nuclear matter3, and independently measure the local expansion rate of the Universe4. Here, we present the optical follow-up and analysis of two of the only three high-significance NSBH merger candidates detected to date, S200105ae and S200115j, with the Zwicky Transient Facility5. The Zwicky Transient Facility observed ~48% of S200105ae and ~22% of S200115j’s localization probabilities, with observations sensitive to kilonovae brighter than −17.5 mag fading at 0.5 mag d−1 in the g- and r-bands; extensive searches and systematic follow-up of candidates did not yield a viable counterpart. We present state-of-the-art kilonova models tailored to NSBH systems that place constraints on the ejecta properties of these NSBH mergers. We show that with observed depths of apparent magnitude ~22 mag, attainable in metre-class, wide-field-of-view survey instruments, strong constraints on ejecta mass are possible, with the potential to rule out low mass ratios, high black hole spins and large neutron star radii.

Relativistic accretion disc reflection in AGN X-ray spectra at z = 0.5–4: a study of four Chandra Deep Fields

ABSTRACT We confirm that the spectra are best fit by a model containing two Compton reflection components, one from distant material, and the other displaying relativistic broadening, most likely from the inner accretion disc. The degree of relativistic broadening indicates a preference for high black hole spin, but the reflection is weaker than that expected for a flat disc illuminated by a point source. We investigate the Compton reflection signatures as a function of luminosity, redshift, and obscuration, confirming an X-ray Baldwin effect for both the narrow and broad components of the iron line. Anticorrelations are also seen with redshift and obscuring column density, but are difficult to disentangle from the Baldwin effect. Our methodology is able to extract information from multiple spectra with low signal-to-noise ratio (SN), and can be applied to future data sets such as eROSITA. We show using simulations, however, that it is necessary to apply an appropriate S/N cut to the samples to ensure the spectra add useful information.