Observations Of Supermassive Black Holes Research Articles

Constraints on thermalizing surfaces from infrared observations of supermassive black holes

Infrared observations of Sgr A* and M87* are incompatible with the assumption that these sources have physical surfaces in thermal equilibrium with their accreting environments. In this paper we discuss a general parametrization of the energy balance in a horizonless object, which permits to quantify how close a horizonless object is in its behavior to a black hole, and analyze the timescale in which its surface can thermalize. We show that the thermalization timescale is unbounded, growing large for objects that mimic closely the behavior of a black hole (and being infinite for the latter). In particular, the thermalization timescale is proportional to the time that energy spends inside the horizonless object due to propagation and interactions with the bulk. Hence, these observations can be used to quantitatively restrict the dynamical behavior of horizonless objects, without being able to discard the existence of a physical surface.

Constraints on the Cosmological Coupling of Black Holes from the Globular Cluster NGC 3201

Globular clusters are among the oldest stellar populations in the Milky Way; consequently, they also host some of the oldest known stellar-mass black holes, providing insight into black hole formation and evolution in the early (z ≳ 2) universe. Recent observations of supermassive black holes in elliptical galaxies have been invoked to suggest the possibility of a cosmological coupling between astrophysical black holes and the surrounding expanding universe, offering a mechanism for black holes to grow over cosmic time and potentially explaining the origin of dark energy. In this paper, I show that the mass functions of the two radial velocity black hole candidates in NGC 3201 place strong constraints on the cosmologically coupled growth of black holes. In particular, the amount of coupling required to explain the origin of dark energy would either require both NGC 3201 black holes to be nearly face on (a configuration with probability of at most 10−4) or one of the BHs would need to have formed with a mass below that of the most massive neutron stars (2.2 M ⊙). This emphasizes that these and other detached black hole–star binaries can serve not only as laboratories for compact object and binary astrophysics but as constraints on the long-term evolution of astrophysical black holes.

Revisiting the Affleck-Dine mechanism for primordial black hole formation

We study a primordial black hole (PBH) formation scenario based on the Affleck-Dine (AD) mechanism and investigate two PBH mass regions: M ∼ 30 M ⊙ motivated by the LIGO-Virgo observations of the binary black hole mergers and M ≳ 104 M ⊙ motivated by the observations of supermassive black holes at the center of galaxies. In the previous studies, it has been considered that the inhomogeneous AD baryogenesis generates regions with a large baryon asymmetry, some of which collapse into PBHs. In this paper, we show that this scenario is severely constrained due to the baryon asymmetry remaining outside PBHs, which would spoil the success of the big bang nucleosynthesis. Then, we propose an alternative scenario where the AD leptogenesis results in the inhomogeneous formation of Q-balls with lepton charges, which collapse into PBHs. As a result, we find that our scenario can explain the favorable PBH abundance without conflicting with the observational constraints.

Double flows anchored in a Kerr black hole horizon – I. Meridionally self-similar MHD models with loading terms

ABSTRACT Recent observations of supermassive black holes have brought us new information on their magnetospheres. In this study, we attempt a theoretical modelling of the coupling of black holes with their jets and discs, via three innovations. First, we propose a semi-analytical MHD description of a steady relativistic inflow–outflow structure characteristic to the extraction of the hole rotational energy. The mass-loading is ensured in a thin layer, the stagnation surface, by a two-photon pair production originating to a gamma-ray emission from the surrounding disc. The double flow is described near the polar axis by an axisymmetric meridionally self-similar MHD model. Secondly, the inflow and outflow solutions are crossing the MHD critical points and are matched at the stagnation surface. Knowledge of the MHD field on the horizon gives us the angular momentum and energy extracted from the black hole. Finally, we illustrate the model with three specific examples of double-flow solutions by varying the energetic interaction between the MHD field and the rotating black hole. When the isorotation frequency is half of the black hole one, the extracted Poynting flux is comparable to the one obtained using the force-free assumption. In two of the presented solutions, the Penrose process dominates at large colatitudes, while the third is Poynting flux dominated at mid-colatitudes. Mass injection rate estimations, from disc luminosity and inner radius, give an upper limit just above the values obtained for two solutions. This model is pertinent to describe the flows near the polar axis, where pair production is more efficient.

Equatorial orbits and imaging of hairy cubic Galileon black holes

Null and timelike equatorial orbits are investigated in a family of hairy black holes in the cubic Galileon theory. These include rotating generalizations of static black hole metrics supporting a time-dependent scalar field. Depending on the coupling and rotation, the properties of the geodesics expectedly deviate from general relativity. In particular, it is found that stable circular geodesics only exist below a critical coupling, which is related to the existence of an outermost stable circular orbit. Focusing on the strong-field region, images of an accretion disk are also produced to highlight tendencies that would constrain the model given further accurate observations of supermassive black holes.

Angular correlation as a novel probe of supermassive primordial black holes

We investigate the clustering property of primordial black holes (PBHs) in a scenario where PBHs can explain the existence of supermassive black holes (SMBHs) at high redshifts. We analyze the angular correlation function of PBHs originating from fluctuations of a spectator field which can be regarded as a representative model to explain SMBHs without conflicting with the constraint from the spectral distortion of cosmic microwave background. We argue that the clustering property of PBHs can give a critical test for models with PBHs as the origin of SMBHs and indeed show that the spatial distribution of PBHs in such a scenario is highly clustered, which suggests that those models may be disfavored from observations of SMBHs although a careful comparison with observational data would be necessary.

The Effects of Tilt on the Images of Black Hole Accretion Flows

Abstract We analyze two 3D general-relativistic magnetohydrodynamic accretion simulations in the context of how they would manifest in Event Horizon Telescope (EHT) observations of supermassive black holes. The two simulations differ only in whether the initial angular momentum of the plasma is aligned with the rapid (a = 0.9) spin of the black hole. Both have low net magnetic flux. Ray tracing is employed to generate resolved images of the synchrotron emission. When using parameters appropriate for Sgr A* and assuming a viewing angle aligned with the black hole spin, we find the most prominent difference is that the central shadow in the image is noticeably eccentric in tilted models, with the ring of emission relatively unchanged. Applying this procedure to M87 with a viewing angle based on the large-scale jet, we find that adding tilt increases the angular size of the ring for fixed black hole mass and distance, while at the same time increasing the number of bright spots in the image. Our findings illustrate observable features that can distinguish tilted from aligned flows. They also show that tilted models can be viable for M87, and that not accounting for tilt can bias inferences of physical parameters. Future modeling of horizon-scale observations should account for potential angular momentum misalignment, which is likely generic at the low accretion rates appropriate for EHT targets.

Interferometric observations of supermassive black holes in the millimeter wave band

We present a theoretical description of different types of accretion disks and jets near supermassive black holes (SMBHs) that can be observed in the (sub)millimeter wave band. Special attention is paid to the possible formation of the shadow of a black hole illuminated by an accretion disk or a jet. We suggest a simple criterion for identifying such a shadow in current and planned SMBH observations using very long baseline interferometry (VLBI). As an example, we propose a number of potential SMBH candidates satisfying this criterion for observations with the future Millimetron space observatory in the VLBI regime and with the Event Horizon Telescope.

A radio telescope in the Arctic region

A former ALMA prototype antenna has a new lease of life in the harsh conditions of Greenland, where it will play a key role in very-long-baseline interferometry observations of supermassive black holes, explain Nimesh Patel and Paul Ho.

Black hole shadow as a test of general relativity: quadratic gravity

Observations of the black hole shadow of supermassive black holes, such as Sagittarius A* at the center of our Milky Way galaxy, allow us to study the properties of black holes and the nature of strong-field gravity. According to the Kerr hypothesis, isolated, stationary, and axisymmetric astrophysical black holes are described by the Kerr metric. The Kerr hypothesis holds in general relativity and in some modified gravity theories, but there are others in which it is violated. In principle, black hole shadow observations can be used to determine if the Kerr metric is the correct description for black holes, and in turn, they could be used to place constraints on modified gravity theories that do not admit the Kerr solution. We here investigate whether black hole shadow observations can constrain deviations from general relativity, focusing on two well-motivated modified quadratic gravity theories: Einstein-dilaton-Gauss–Bonnet gravity and dynamical Chern–Simons gravity. We show that current constraints on Einstein-dilaton-Gauss–Bonnet gravity are stronger than any that could be placed with black hole shadow observations of supermassive black holes. We also show that the same holds for dynamical Chern–Simons gravity through a systematic bias and a likelihood analysis when considering slowly-rotating supermassive black holes. However, observations of more rapidly-rotating black holes, with dimensionless spins , could be used to better constrain dynamical Chern–Simons gravity.

Интерферометричекие наблюдения сверхмассивных черных дыр в миллиметровом диапазоне

Интерферометричекие наблюдения сверхмассивных черных дыр в миллиметровом диапазоне

Testing theories of modified gravity

With further refinement, observations of supermassive black holes could test the presence of a universal scalar field. With further refinement, observations of supermassive black holes could test the presence of a universal scalar field.

Imaging black holes with sparse modeling

We introduce a new imaging method for radio interferometry based on sparse- modeling. The direct observables in radio interferometry are visibilities, which are Fourier transformation of an astronomical image on the sky-plane, and incomplete sampling of visibilities in the spatial frequency domain results in an under-determined problem, which has been usually solved with 0 filling to un-sampled grids. In this paper we propose to directly solve this under-determined problem using sparse modeling without 0 filling, which realizes super resolution, i.e., resolution higher than the standard refraction limit. We show simulation results of sparse modeling for the Event Horizon Telescope (EHT) observations of super-massive black holes and demonstrate that our approach has significant merit in observations of black hole shadows expected to be realized in near future. We also present some results with the method applied to real data, and also discuss more advanced techniques for practical observations such as imaging with closure phase as well as treating the effect of interstellar scattering effect.

Radial structure, inflow and central mass of stationary radiative galaxy clusters

We analyse the radial structure of self-gravitating spheres consisting of multiple interpenetrating fluids, such as the X-ray emitting gas and the dark halo of a galaxy cluster. In these dipolytropic models, the adiabatic dark matter sits in equilibrium, while the gas develops a gradual, smooth, quasi-stationary cooling flow. Both affect and respond to the collective gravitational field. We find that all subsonic, radially continuous, steady solutions require a non-zero minimum central point mass. For Mpc-sized haloes with 7–10 effective degrees of freedom (F2), the minimum central mass is compatible with observations of supermassive black holes. Smaller gas mass influxes enable smaller central masses for wider ranges of F2. The halo comprises a sharp spike around the central mass, embedded within a core of nearly constant density (at 101–102.5 kpc scales), with outskirts that attenuate and naturally truncate at finite radius (several Mpc). The gas density resembles a broken power law in radius, but the temperature dips and peaks within the dark core. A finite minimum temperature occurs due to gravitational self-warming, without cold mass dropout nor needing regulatory heating. X-ray emission from the intracluster medium mimics a β-model plus bright compact nucleus. Near-sonic points in the gas flow are bottlenecks to the allowed steady solutions; the outermost are at kpc scales. These sites may preferentially develop cold mass dropout during strong perturbations off equilibrium. Within the sonic point, the profile of gas specific entropy is flatter than s∝r1/2, but this is a shallow ramp and not an isentropic core. When F2 is large, the inner halo spike is only marginally Jeans stable in the central parsec, suggesting that a large non-linear disturbance could trigger local dark collapse on to the central object.

Retaining Black Holes with Very Large Recoil Velocities

Recent numerical simulations of binary black hole mergers show the possibility of producing very large recoil velocities (> 3000 km/s). Kicks of this magnitude should be sufficient to eject the final black hole from virtually any galactic potential. This result has been seen as a potential contradiction with observations of supermassive black holes residing in the centers of most galaxies in the local universe. Using an extremely simplified merger tree model, we show that, even in the limit of very large ejection probability, after a small number of merger generations there should still be an appreciable fraction (>50%) of galaxies with supermassive black holes today. We go on to argue that the inclusion of more realistic physics ingredients in the merger model should systematically increase this retention fraction, helping to resolve a potential conflict between theory and observation. Lastly, we develop a more realistic Monte Carlo model to confirm the qualitative arguments and estimate occupation fractions as a function of the central galactic velocity dispersion.

Workshop on gravitational waves and relativistic astrophysics

Discussions related to gravitational wave experiments viz. LIGO and LISA as well as to observations of supermassive black holes dominated the workshop sessions on gravitational waves and relativistic astrophysics in the ICGC-2004. A summary of seven papers that were presented in these workshop sessions has been provided in this article.