Nature Of Black Holes Research Articles

Phase transition and quantum corrections of quintessential Kerr–Newman black hole with cloud of strings

The purpose of this manuscript is to inspecting the phase transition and the critical phenomenon of charged quintessential Kerr-Newman-anti-de Sitter black hole with cloud of strings. In this regard, we evaluate the thermodynamic factors (Hawking temperature, angular momentum and entropy) in the framework of extended phase space. These factors fulfill the Smarr-Gibbs-Dehum equation in the existence of quintessence and cloud of strings. The critical behavior of thermodynamic factors is discussed via two techniques such as Maxwell equal-area law and Van-der Waal like equation of state . It is obtained that the former one is more effective to observe the critical nature of the complex black holes. Further, we study the phase diagram in T − S plane using equal-area law and obtain an isobar depicting the coexistence era of two phases. It is concluded that black holes lower than the critical temperature exhibit the phase transition same as that of Van-der Waal fluid. At the end, we analyze the influence of thermal variations on the black hole’s stability. • We inspect the critical phenomenon of quintessential string Kerr-Newman-AdS BH. • The critical behavior via Maxwell equal-area law and Van-der Waal EoS is studied. • Below the critical temperature, BHs show the VdW fluid like phase transition. • At the end, we analyze the influence of thermal variations on the black hole’s stability.

Way down in the hole… and up again

I argue that an approach which uses an appropriate admixture of both classical and semiclassical effects is essential for understanding the ultimate fate of gravitational collapse and the nature of black holes (BHs). I provide an example of a problem which pushes the boundaries of what is known in both the classical and semiclassical approaches: the evolution of the inner horizon of a BH. I show that solving this problem requires considering perturbations of both classical and semiclassical origins. In fact, it has been found that classical mass inflation might be counteracted by a semiclassical tendency for the inner horizon to inflate outward.

Why do we study black holes?

<p indent="0mm">Black holes are arguably the most mysterious object in the universe. They are an important research subject in physics and astronomy, as well as a favorite topic among the general public. The concept was conceived in the 18th century based on the mathematical form of Newton’s gravitational theory. Now, more than <sc>200 years</sc> later, black-hole research has evolved from pure mathematical speculation to a “hard-core’’ science with sound theoretical and observational foundations. Many Noble prizes in physics were, in some degree, related to black holes. In particular, not long into the 21st century, three Nobels prizes in physics have been awarded to the studies directly related to black holes. Why is an object seemingly so disconnected with daily life attracting so much attention from the scientific community? By reviewing some of the most important breakthroughs over the history of studying black holes, I will try to show the readers that black-hole research is important. First, it has shaped our perception of space and time. The theory of general relativity predicts the existence, at least in theory, of black holes. However, it cannot self-consistently explain the existence of a singularity which is bound to form at the “center’’ of a black hole. The motivation of resolving the singularity problem has inspired the later studies of the quantum nature of black holes, but has also led to the discovery of the paradox of information loss. The potential solution of such a paradox has pointed to a more fundamental relationship between quantum mechanics and the nature of spacetime. Second, it has inspired a chain of scientific discoveries. Here, I will focus on the discoveries made by astronomers. I will show that the different approaches adopted by astronomers have given rise to a series of breakthroughs in black-hole research. These discoveries not only proved that black holes exist in our university, but also have greatly enriched our understanding of the formation and evolution of stars, galaxies, and even the whole universe. Third, black-hole research has triggered major technological developments in various fields. I will show that the history of discovering black holes is closely tied to the development of radio astronomy, X-ray detectors, measurement theory, as well as quantum technology. In particular, the requirements raised by the observation of black holes have, in turn, driven many technological breakthroughs. These breakthroughs have also resulted in inventions which have become important in our daily life. China is currently running and also planning many large-scale astronomy projects which list black holes as one of their major targets. These projects will place China in the forefront of scientific exploration and technological innovation, and probably open a new era of black-hole revolution.

Effective theory of quantum black holes

We explore the quantum nature of black holes by introducing an effective framework that takes into account deviations from the classical results. The approach is based on introducing quantum corrections to the classical Schwarzschild geometry in a way that is consistent with the physical scales of the black hole and its classical symmetries. This is achieved by organizing the quantum corrections in inverse powers of a physical distance. By solving the system in a self-consistent way we show that the derived physical quantities, such as event horizons, temperature and entropy can be expressed in a well-defined expansion in the inverse powers of the black hole mass. The approach captures the general form of the quantum corrections to black hole physics without requiring us to commit to a specific model of quantum gravity.

Black holes decohere quantum superpositions

We show that if a massive body is put in a quantum superposition of spatially separated states, the mere presence of a black hole in the vicinity of the body will eventually destroy the coherence of the superposition. This occurs because, in effect, the gravitational field of the body radiates soft gravitons into the black hole, allowing the black hole to acquire “which path” information about the superposition. A similar effect occurs for quantum superpositions of electrically charged bodies. We provide estimates of the decoherence time for such quantum superpositions. We believe that the fact that a black hole will eventually decohere any quantum superposition may be of fundamental significance for our understanding of the nature of black holes in a quantum theory of gravity.

An Isolated Stellar-mass Black Hole Detected through Astrometric Microlensing* *This research is based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

We report the first unambiguous detection and mass measurement of an isolated stellar-mass black hole (BH). We used the Hubble Space Telescope (HST) to carry out precise astrometry of the source star of the long-duration (t E ≃ 270 days), high-magnification microlensing event MOA-2011-BLG-191/OGLE-2011-BLG-0462 (hereafter designated as MOA-11-191/OGLE-11-462), in the direction of the Galactic bulge. HST imaging, conducted at eight epochs over an interval of 6 yr, reveals a clear relativistic astrometric deflection of the background star’s apparent position. Ground-based photometry of MOA-11-191/OGLE-11-462 shows a parallactic signature of the effect of Earth’s motion on the microlensing light curve. Combining the HST astrometry with the ground-based light curve and the derived parallax, we obtain a lens mass of 7.1 ± 1.3 M ⊙ and a distance of 1.58 ± 0.18 kpc. We show that the lens emits no detectable light, which, along with having a mass higher than is possible for a white dwarf or neutron star, confirms its BH nature. Our analysis also provides an absolute proper motion for the BH. The proper motion is offset from the mean motion of Galactic disk stars at similar distances by an amount corresponding to a transverse space velocity of ∼45 km s−1, suggesting that the BH received a “natal kick” from its supernova explosion. Previous mass determinations for stellar-mass BHs have come from radial velocity measurements of Galactic X-ray binaries and from gravitational radiation emitted by merging BHs in binary systems in external galaxies. Our mass measurement is the first for an isolated stellar-mass BH using any technique.

Testing gravity with black hole shadow subrings

The black hole shadow, first observed by the Event Horizon Telescope in 2017, is the newest method for studying black holes and understanding gravity. Much work has gone into understanding the shadow of a Kerr black hole, including all of the complex astrophysics of the accretion disk, and there are numerous studies of the ideal shadow in non-Kerr black holes and exotic compact objects. This paper presents one of the first studies of the black hole shadow of non-Kerr black holes when the illumination source is an accretion disk. In particular, the ability of current and future very long baseline interferometers to estimate the physical parameters of the black hole spacetime and accretion disk is investigated using two different parametrized black hole metrics that encode a number of possible deviations from Kerr. Both the full shadow image and the individual subrings of the shadow are analyzed as the higher order subrings are weakly dependent on the disk physics and may be a more viable observable for studying the spacetime. The results suggest that with current telescope capabilities and any future earth-based telescopes it will be quite difficult to place strong constraints on departures from the Kerr spacetime, primarily due to the low resolution and strong degeneracies between the spacetime parameters. More optimistically, space-based interferometers may be capable of testing the Kerr nature of black holes and general relativity to comparable or better precision than is currently possible with other observations.

New kind of echo from quantum black holes

We propose that a quantum black hole can produce a new kind of late-time gravitational echoes, facilitated by a near-horizon process analogous to Andreev reflection in condensed matter systems. In comparison to the traditional echo scenarios where the near-horizon region is treated as an ordinary reflector, we argue that, consequent to near-horizon gravitational scattering, this region is better described by an Andreev reflector. Such interactions lead to a novel contribution to gravitational echoes with a characteristic phase difference, an effect which is analogous to how Andreev reflections lead to propagating particle-like and hole-like components with a relative phase in certain condensed matter scenarios. Moreover, this novel contribution to the echo signal encodes information about the `near-horizon quantum state', hence offering a possible new window to probe the quantum nature of black holes.

Unveiling the nature of SgrA* with the geodesic motion of S-stars

Despite the huge improvements guaranteed by future GRAVITY observations of the S0-2 star, these will not be able to unveil the fundamental nature, whether black hole or wormhole, of the central supermassive object. Nevertheless, observing stars orbiting closer to the central gravitational source could allow to distinguish between the black hole and wormhole nature of this object at more than 5σ. Firstly, we have used publicly available astrometric and spectroscopic measurements of the S0-2 star to constrain the metric around the supermassive object without finding any evidence either favouring or ruling out the wormhole nature. Secondly, we have designed a mock catalogue of future observations of the S0-2 star mirroring the accuracy and precision of GRAVITY. Afterwards, we firstly tested our methodology showing that our procedure recovers the input model, and subsequently we demonstrated that the constraining power of such a dataset is not enough to distinguish between black hole and wormhole. Finally, we built some toy models representing stars orbiting much closer the central object than S0-2. We used these toy models to investigate which are the ideal orbital features and observational strategies to achieve our aim of unveiling the fundamental nature of the central supermassive object, demonstrating that a star with a period of the order of ∼ 5 years and a pericentre distance of ∼ 5 AU could identify the nature of the central object at almost 5σ accuracy.

Hard-state Optical Wind during the Discovery Outburst of the Black Hole X-Ray Dipper MAXI J1803–298

Abstract We present 12 epochs of optical spectroscopy taken across the discovery outburst of the black hole (BH) candidate MAXI J1803−298 with the Gran Telescopio Canarias and Very Large Telescope. The source followed a standard outburst evolution with hard and soft states. The system displays a triangular shape in the hardness intensity diagram, consistent with that seen in high-inclination BH transients and the previously reported detection of X-ray dips. The two epochs observed during the initial hard state exhibited asymmetric emission-line profiles, including a P-Cygni profile simultaneously detected in Hα and He i 6678, which indicates the presence of an optical wind in the system. The remaining spectra, obtained during the transition to the soft state and the subsequent decay, are instead characterized by narrower, double-peaked emission lines embedded into broad absorption components. One epoch (intermediate state) also includes near-infrared (NIR) coverage, revealing complex line profiles in the Paschen and Bracket series, which suggests that the outflow is still present during the outburst decay through the soft state. The growing list of low-mass X-ray binaries with optical and NIR outflow signatures indicates that these are common features. Furthermore, the lowest luminosity spectrum exhibits an Hα FWHM of 1570 ± 100 km s−1. This, together with previous constraints on the binary parameters, allows us to favor a compact object mass of ∼3–10 M ⊙, further supporting its BH nature.

Reshaping our understanding on structure formation with the quantum nature of the dark matter

We study the nonlinear structure formation in cosmology accounting for the quantum nature of the dark matter (DM) particles in the initial conditions at decoupling, as well as in the relaxation and stability of the DM halos. Different from cosmological N-body simulations, we use a thermodynamic approach for collisionless systems of self-gravitating fermions in general relativity, in which the halos reach the steady state by maximizing a coarse-grained entropy. We show the ability of this approach to provide answers to crucial open problems in cosmology, among others: the mass and nature of the DM particle, the formation and nature of supermassive black holes in the early Universe, the nature of the intermediate mass black holes in small halos, and the core-cusp problem.

A Novel Explanation for the Arrangement of the Universe–Solar System–Planets–Earth. Part 3

New ideas are presented about the nature of the evolution of the Universe, which call for a deeper scientific understanding and reassessment of the existing views on the so-called Big Bang cosmological model. According to this model, the Universe has now been expanding for ~20 Ga, with the lightest elements forming during the first few seconds at T ~ 109 K as a result of nuclear fusion. These elements are H, D, and 3,4He; at first, hydrogen turns into helium, and then helium transforms into carbon, oxygen, nitrogen, etc., up to iron group elements. The probability is examined of the action of attraction forces due to electromagnetic interaction of rotating charged baryonic particles, instead of the classical Newton theory of gravitation, i.e., the law describing gravitational interaction in classical mechanics. A discussion is provided of the nature and role of black holes in the Universe, which are seen as an integral and obligatory part of all physical structures of the Cosmos. So far, no theory has been able to fully describe the internal structure of black holes; however, as follows from the Planck and Boltzmann laws, these holes are a perpetuum mobile of evolution for the entire Universe, controlling the transformation mechanism through electromagnetic resonance oscillations of the entire cosmic ether (like the human brain), which propagate across all structures of the Universe. Space objects are Earth-like planets with a solid core, liquid mantle, and a hard crust, above which the atmosphere immediately begins; gas giants with no solid surface (a substantial part of them is the atmosphere, which at low altitudes turns into a liquid due to increased pressure, while there is no clear boundary between the liquid ocean and the atmosphere); and stars, all of which have a solid core and poles synchronized with black holes. Although our conceptions about the existence of dark matter and dark energy in the Universe still remain the most mysterious ones, we argue that the bulk of matter and energy is concentrated in cosmic–plasma electromagnetic fields (>95%). All stars and planets must be increasing in volume with time while retaining their angular momentum and position in space. Both space and time are equivalent to each other and are the most uncertain and multivector universal functions of the Universe. They change simultaneously and proportionally with the form of existence of matter, which inevitably leads to the emergence of a fundamentally new quality—life. Living beings evolve and acquire spirituality, i.e., the ability to cognize not only themselves but the surrounding world. However, space–time is an extremely complex system, yet to be understood by new generations of scientists: physicists, cosmologists, and others.

The astrophysics of rotational energy extraction from a black hole

Recent work has called into question whether nature can extract the rotational energy of a black hole via electromagnetic fields by appealing to an alleged ability to absorb current. We describe the strategies needed to properly treat the astrophysics in curved spacetime near black holes, showing that while the Blandford-Znajek effect is sound, the deeper nature of the electric nature of black holes remains unresolved.

Inference with finite time series: Observing the gravitational Universe through windows

Time series analysis is ubiquitous in many fields of science including gravitational-wave astronomy, where strain time series are analyzed to infer the nature of gravitational-wave sources, e.g., black holes and neutron stars. It is common in gravitational-wave transient studies to apply a tapered window function to reduce the effects of spectral artifacts from the sharp edges of data segments. We show that the conventional analysis of tapered data fails to take into account covariance between frequency bins, which arises for all finite time series---no matter the choice of window function. We discuss the origin of this covariance and derive a framework that models the correlation induced by the window function. We demonstrate this solution using both simulated Gaussian noise and real Advanced LIGO/Advanced Virgo data. We show that the effect of these correlations is similar in scale to widely studied systematic errors, e.g., uncertainty in detector calibration and power spectral density estimation.

Image features of spinning regular black holes based on a locality principle

To understand the true nature of black holes, fundamental theoretical developments should be linked all the way to observational features of black holes in their natural astrophysical environments. Here, we take several steps to establish such a link. We construct a family of spinning, regular black-hole spacetimes based on a locality principle for new physics and analyze their shadow images. We identify characteristic image features associated to regularity (increased compactness and relative stretching) and to the locality principle (cusps and asymmetry) that persist in the presence of a simple analytical disk model. We conjecture that these occur as universal features of distinct classes of regular black holes based on different sets of construction principles for the corresponding spacetimes.

Effective thermodynamical system of Schwarzschild–de Sitter black holes from Rényi statistics

It has been known that the Schwarzschild-de Sitter (Sch-dS) black hole may not be in thermal equilibrium and also be found to be thermodynamically unstable in the standard black hole thermodynamics. In the present work, we investigate the possibility to realize the thermodynamical stability of the Sch-dS black hole as an effective system by using the R\'{e}nyi statistics, which includes the non-extensive nature of black holes. Our results indicate that the non-extensivity allows the black hole to be thermodynamically stable which gives rise to the lower bound on the non-extensive parameter. By comparing the results to ones in the separated system approach, we find that the effective temperature is always smaller than the black hole horizon temperature and the thermodynamically stable black hole in effective approach is always larger than one in separated approach at a certain temperature. There exists only the zeroth-order phase transition from the the hot gas phase to the black hole phase for the effective system while it is possible to have the transition of both the zeroth order and the first order for the separated system.

Qualifying ringdown and shadow of black holes under general parametrized metrics with photon orbits

The motion of photons around black holes determines the shape of shadow and match the ringdown properties of a perturbed black hole. Observations of shadows and ringdown waveforms will reveal the nature of black holes. In this paper, we study the motion of photons in a general parametrized metric beyond the Kerr hypothesis. We investigated the radius and frequency of the photon circular orbits on the equatorial plane and obtained fitted formula with varied parameters. The Lyapunov exponent which connects to the decay rate of the ringdown amplitude is also calculated. We also analyzed the shape of shadow with full parameters of the generally axisymmetric metric. Our results imply the potential constraint on black hole parameters by combining the Event Horizon Telescope and gravitational wave observations in the future.

Dynamical confirmation of a stellar mass black hole in the transient X-ray dipping binary MAXI J1305-704

ABSTRACT MAXI J1305-704 has been proposed as a high-inclination candidate black hole X-ray binary in view of its X-ray properties and dipping behaviour during outburst. We present photometric and spectroscopic observations of the source in quiescence that allow us to reveal the ellipsoidal modulation of the companion star and absorption features consistent with those of an early K-type star ($T_{\rm eff}=4610^{+130}_{-160}\, {\rm K}$). The central wavelengths of the absorption lines vary periodically at $P_{\rm orb}=0.394\pm 0.004\, {\rm d}$ with an amplitude of $K_2=554\pm 8\, {\rm km \, s^{-1}}$. They imply a mass function for the compact object of $f(M_1)=6.9\pm 0.3\, {\rm M}_\odot$, confirming its black hole nature. The simultaneous absence of X-ray eclipses and the presence of dips set a conservative range of allowed inclinations $60\, {\rm deg}\lt i\lt 82\, {\rm deg}$, while modelling of optical light curves further constrain it to $i=72^{+5}_{-8}\, {\rm deg}$. The above parameters together set a black hole mass of $M_1= 8.9_{-1.0}^{+1.6}\, {\rm M}_{\odot }$ and a companion mass of $M_2= 0.43\pm 0.16\, {\rm M}_{\odot }$, much lower than that of a dwarf star of the observed spectral type, implying it is evolved. Estimates of the distance to the system ($d=7.5^{+1.8}_{-1.4}\, {\rm kpc}$) and space velocity ($v_{\rm space}=270\pm 60 \, {\rm km\, s^{-1}}$) place it in the Galactic thick disc and favour a significant natal kick during the formation of the BH if the supernova occurred in the Galactic Plane.

Probing the nature of black holes: Deep in the mHz gravitational-wave sky

Black holes are unique among astrophysical sources: they are the simplest macroscopic objects in the Universe, and they are extraordinary in terms of their ability to convert energy into electromagnetic and gravitational radiation. Our capacity to probe their nature is limited by the sensitivity of our detectors. The LIGO/Virgo interferometers are the gravitational-wave equivalent of Galileo’s telescope. The first few detections represent the beginning of a long journey of exploration. At the current pace of technological progress, it is reasonable to expect that the gravitational-wave detectors available in the 2035-2050s will be formidable tools to explore these fascinating objects in the cosmos, and space-based detectors with peak sensitivities in the mHz band represent one class of such tools. These detectors have a staggering discovery potential, and they will address fundamental open questions in physics and astronomy. Are astrophysical black holes adequately described by general relativity? Do we have empirical evidence for event horizons? Can black holes provide a glimpse into quantum gravity, or reveal a classical breakdown of Einstein’s gravity? How and when did black holes form, and how do they grow? Are there new long-range interactions or fields in our Universe, potentially related to dark matter and dark energy or a more fundamental description of gravitation? Precision tests of black hole spacetimes with mHz-band gravitational-wave detectors will probe general relativity and fundamental physics in previously inaccessible regimes, and allow us to address some of these fundamental issues in our current understanding of nature.

Hinting a dark matter nature of Sgr A* via the S-stars

ABSTRACT The motion data of the S-stars around the Galactic Centre gathered in the last 28 yr imply that Sgr A* hosts a supermassive compact object of about $4 \times 10^6\, {\rm M}_{\odot }$, a result awarded with the Nobel Prize in Physics 2020. A non-rotating black hole (BH) nature of Sgr A* has been uncritically adopted since the S-star orbits agree with Schwarzschild geometry geodesics. The orbit of S2 has served as a test of general relativity predictions such as the gravitational redshift and the relativistic precession. The central BH model is, however, challenged by the G2 post-peripassage motion and by the lack of observations on event-horizon-scale distances robustly pointing to its univocal presence. We have recently shown that the S2 and G2 astrometry data are better fitted by geodesics in the spacetime of a self-gravitating dark matter core–halo distribution of 56 keV-fermions, ‘darkinos’, which also explains the outer halo Galactic rotation curves. This letter confirms and extends this conclusion using the astrometry data of the 17 best-resolved S-stars, thereby strengthening the alternative nature of Sgr A* as a dense core of darkinos.