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Black hole chasers : the amazing true story of an astronomical breakthrough
Presents the true story of one of the Event Horizon Telescope team's reveal of the first image of a super massive black hole\"--Provided by publisher.
Book
Event Horizon and Environs (ETHER): A Curated Database for EHT and ngEHT Targets and Science
The next generation Event Horizon Telescope (ngEHT) will observe multiple supermassive black hole (SMBH) candidates down to a few tens of mJy, and profoundly transform our understanding of the local SMBH population. Given the impossibility of large-area high-resolution millimeter surveys, multi-frequency spectral energy densities (SEDs), and models are required to both identify source samples tailored to specific science goals, and to predict the feasibility of detection of individual interesting sources. Here, we present the Event Horizon and Environs (ETHER) source and SED model database whose primary use is to enable the selection and optimization of targets for EHT and ngEHT science. The living ETHER database currently consolidates 1.6 million black hole mass estimates, ∼15,500 milliarcsec-scale radio fluxes, ∼14,000 hard X-ray fluxes (expected to grow by factor ≳40 with the eROSITA data release) and SED information as obtained from catalogs and database queries, the literature, and our own new observations. Jet and accretion flow models are fit to individual SEDs in an automated way in order to predict the ngEHT observable fluxes from the jet base and accretion inflow. The database can be filtered by parameters or cross matched to a user source list, with the automated SED fitting models optionally fine tuned by the user. We have identified an initial ngEHT ‘gold sample’ for jet base studies and potentially black hole shadows; this sample will grow significantly in the coming years. While the ngEHT requires and will best exploit the ETHER database, six (eleven) ETHER sources have already been observed (scheduled) with the EHT in 2022 (2023), and the database has wide ranging applications in galaxy and black hole mass evolution studies.
Journal Article
Black holes, Cauchy horizons, and mass inflation
Event horizons and Cauchy horizons are highly idealized mathematical constructions that do not fully capture the key physics of either Hawking radiation or mass inflation. Indeed, because they are teleological, both event horizons and Cauchy horizons are (in a precise technical sense) not physically observable. In contrast, by inspecting the quasi-local behaviour of null geodesics, long-lived apparent horizons (or more generally long-lived quasi-local horizons) are in principle physically observable, and are “good enough\" for then pragmatically redefining a black hole, and “good enough” for generating Hawking radiation. Furthermore it is now also clear that long lived apparent horizons (quasi-local horizons) are also “good enough\" for generating mass inflation. These observations suggest that one should be somewhat careful when trying to extrapolate rigorous mathematical theorems, which often embody mathematical idealizations that do not necessarily correspond to what a finite resource astronomer can actually measure, into the astrophysical realm.
Journal Article
Quantum properties of fermionic fields in multi-event horizon spacetime
We investigated the properties of quantum entanglement and mutual information in the multi-event horizon Schwarzschild-de Sitter (SdS) spacetime for massless Dirac fields. For the first time, we obtained the expression for the evolutions of the quantum state near the black hole event horizon (BEH) and cosmological event horizon (CEH) in the SdS spacetime. Under the Nariai limit, the physically accessible entanglement and mutual information are maximized, and the physically inaccessible correlations are zero. With the increase in temperature of either horizon, the physically accessible correlations experience degradation. Notably, the initial state remains entangled and can be utilized in entanglement-based quantum information processing tasks, which differs from the scalar field case. Furthermore, the degradation of physically accessible correlations is more pronounced for small-mass black holes. In contrast, the physically inaccessible correlations separated by the CEH monotonically increase with the radiation temperature, and such correlations are not decisively influenced by the effect of particle creation at the BEH. Moreover, a similar phenomenon is observed for the inaccessible correlations separated by the BEH. This result differs from the single event spacetime, in which the physically inaccessible entanglement is a monotonic function of the Hawking temperature.
Journal Article
Effeciency of higher dimensional black holes as particle accelerators
The center-of-mass energy of two colliding particles could be arbitrarily high in the vicinity of event horizons of the extremal Myers-Perry black holes if the angular momentum of colliding particles is fine-tuned to the critical values. We investigate the maximum efficiency of two colliding particles in four and six dimensions. The efficiency of collision for two particles near the four-dimensional Kerr black holes is 130%. We show that the efficiency increases to 145% for collision in six dimensions. We also show that the region for the polar angle in which the particle can reach the high energy is larger when the dimension of space-time increases.
Journal Article
Quantum Clones inside Black Holes
A systematic procedure is proposed for better understanding the evolution laws of black holes in terms of pure quantum states. We start with the two opposed regions I and II in the Penrose diagram, and study the evolution of matter in these regions, using the algebra derived earlier from the Shapiro effect in quantum particles. Since this spacetime has two distinct asymptotic regions, one must assume that there is a mechanism that reduces the number of states. In earlier work we proposed that region II describes the angular antipodes of region I, the ‘antipodal identification’, but this eventually leads to contradictions. Our much simpler proposal is now that all states defined in region II are exact quantum clones of those in region I. This indicates more precisely how to restore unitarity by making all quantum states observable, and in addition suggests that generalisations towards other black hole structures will be possible. An apparent complication is that the wave function must evolve with a purely antisymmetric, imaginary-valued Hamiltonian, but this complication can be well-understood in a realistic interpretation of quantum mechanics.
Journal Article
The Evolutionary Versus the All-at-Once Picture of Spacetime
There are two metaphysical pictures of spacetime: The evolutionary picture and the all-at-once picture. According to the evolutionary picture, spacetime is nothing but the evolution of space over time. In contrast, the all-at-once picture considers spacetime as ‘a global, four-dimensional boundary value problem’ that can be solved only in an all-at-once manner, i.e. as a whole which is fundamentally four-dimensional and non-decomposable into spatial and temporal parts. The two most-known formulations of general theory of relativity, i.e. the Hamiltonian (or the canonical) and the Lagrangian (or the standard) formulations, enjoy the evolutionary and all-at-once pictures of spacetime respectively. Here, we have argued that (1) the all-at-once picture is more aligned with the philosophy of relativity theory, i.e. uniting space and time into spacetime, (2) the evolutionary picture is not as general as the all-at-once, since only in special cases, such as globally hyperbolic spacetimes, is it possible to deal with spacetime as the evolution of a spatial slice over time, and (3) the all-at-once picture paves the way to better understanding
four-dimensional
physical entities, like event horizons, which cannot be explained within an evolutionary picture without raising a paradox. Therefore, the evolutionary picture is neither the
fundamentally-true
nor the
naturally-chosen
picture of spacetime. Rather, we choose the evolutionary picture for practical and computational reasons. While the all-at-once picture seems a more appropriate description of the quantum and cosmological reality, the evolutionary picture can be applied occasionally and locally, or quasi-locally, and is not the proper metaphysical picture of spacetime at the fundamental level of reality.
Journal Article
More on Schwarzschild Black Hole with Ultra-Violet Cutoff
Quantum gravity proposals predict the existence of two natural cutoffs, i.e., a minimal measurable length and a maximal measurable momentum in the ultra-violet (UV) regime or Planck scale, which makes the geometry of the Universe to be discrete. UV cutoffs can regularise the high energy scale of the quantum field theories. In this paper, we aim to consider the GUP-modified Schwarzschild black hole metric in the presence of the minimal measurable length and maximal measurable momentum to investigate how these UV cutoffs affect the stability of circular orbits of black hole accretion disks, shadow behavior and deflection angle, redshift of black hole accretion disks, gravitational tidal forces, and the geodetic drift rate. We also, compare the shadow size of the GUP-modified Schwarzschild black hole with the shadow size of the M87* supermassive black hole captured by Event Horizon Telescope (EHT) collaborations to constrain GUP parameter in the setup.
Journal Article
The parameter planes of the spherically symmetric and static relativistic solutions for polytropes
We explore the parameter space of the family of static and spherically symmetric solutions of the Einstein field equations for polytropes, that were presented in a previous paper. This is a four-parameter family of exact solutions, of which one parameter can be factored out, so that there are only three essential free parameters. The solutions are exact in the sense that no approximations are involved, other than those implied by the numerical precision limitations. The primary objectives of this exploration are to establish directly the existence of large collections of specific solutions, and to determine some of their most important properties. For each value of one of the three essential free parameters of the family of solutions, the polytropic index
n
, taken here, for the sake of simplicity, to be either an integer or a half-integer, we define and explore the parameter planes spanned by the other two essential free parameters. In this way, besides establishing their existence, we are also able to classify the solutions according to their overall matter energy density, as well as in terms of their proximity to solutions that display an event horizon. For four values of
n
we successfully establish the allowed regions of the parameter planes, where the solutions not only exist but also correspond to physically acceptable matter. We find that there are solutions within these regions with overall matter energy densities varying all the way from very low to very high, including some that are as close as one may wish to solutions that display an event horizon, and that therefore represent black holes, or extremely dense objects very similar to them.
Journal Article
Imaging supermassive black hole shadows with a global very long baseline interferometry array
The imaging of two supermassive black holes by the Event Horizon Telescope Collaboration proved to a new level the correctness of Einstein's general relativity, regarding its prediction of black hole shadows in the highly curved spacetime regime.
Journal Article