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A black hole is not a hole
Aspiring astronomers can learn what black holes are, what causes them, how scientists first discovered them and more, in an informative science book that includes space paintings, real telescopic images, funny doodles and speech bubbles.
Book
Charged Particle Circular Orbits around Weakly Charged and Magnetized Kerr Black Holes
We study the circular orbits of charged particles around a weakly charged Kerr black hole immersed in a weak, axisymmetric magnetic field. First, we review the circular orbits of neutral particles. We then review the circular orbits of charged particles around a weakly charged Kerr black hole and weakly magnetized Kerr black hole. The case of a weakly magnetized and charged black hole is investigated thereafter. We investigate, in particular, the effect of the electromagnetic forces on the charged particles’ innermost stable circular orbits. We examine the conditions for the existence of negative-energy stable circular orbits and the possibility of the emergence of a gap or double orbit in thin accretion disks. Some of the interesting astrophysical consequences of our findings are discussed as well.
Journal Article
Black holes
\"An examination of the science behind the astronomical phenomena known as black holes, including relevant theories and history-making discoveries as well as topics of current and future research\" \"--Provided by publisher.
Book
First Sagittarius A Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
We present the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A*), the Galactic center source associated with a supermassive black hole. These observations were conducted in 2017 using a global interferometric array of eight telescopes operating at a wavelength of λ = 1.3 mm. The EHT data resolve a compact emission region with intrahour variability. A variety of imaging and modeling analyses all support an image that is dominated by a bright, thick ring with a diameter of 51.8 ± 2.3 μas (68% credible interval). The ring has modest azimuthal brightness asymmetry and a comparatively dim interior. Using a large suite of numerical simulations, we demonstrate that the EHT images of Sgr A* are consistent with the expected appearance of a Kerr black hole with mass ∼4 × 106 M ⊙, which is inferred to exist at this location based on previous infrared observations of individual stellar orbits, as well as maser proper-motion studies. Our model comparisons disfavor scenarios where the black hole is viewed at high inclination (i > 50°), as well as nonspinning black holes and those with retrograde accretion disks. Our results provide direct evidence for the presence of a supermassive black hole at the center of the Milky Way, and for the first time we connect the predictions from dynamical measurements of stellar orbits on scales of 103–105 gravitational radii to event-horizon-scale images and variability. Furthermore, a comparison with the EHT results for the supermassive black hole M87* shows consistency with the predictions of general relativity spanning over three orders of magnitude in central mass.
Journal Article
Black holes : a space discovery guide
\"This book explores the latest discoveries about black holes while also exploring various theories and discoveries throughout history and even looking into the future.\"-- Provided by publisher.
Book
Testing Rotating Regular Metrics with EHT Results of Sgr A
The Event Horizon Telescope (EHT) observation unveiled the first image of supermassive black hole Sgr A* showing a shadow of diameter θ sh = 48.7 ± 7 μas with fractional deviation from the Schwarzschild black hole shadow diameter δ=−0.08−0.09+0.09(VLTI),−0.04−0.10+0.09(Keck) . The Sgr A* shadow size is within 10% of the Kerr predictions, providing us with another tool to investigate the nature of strong-field gravity. We use the Sgr A* shadow observables to constrain metrics of four independent and well-motivated, parametrically different from Kerr spacetime, rotating regular spacetimes and the corresponding no-horizon spacetimes. We present constraints on the deviation parameter g of rotating regular black holes. The shadow angular diameter θ sh within the 1σ region places bounds on the parameters a and g. Together with EHT bounds on the θ sh and δ of Sgr A*, our analysis concludes that the three rotating regular black holes, i.e., Bardeen, Hayward, and Simpson–Visser black holes, and corresponding no-horizon spacetimes agree with the EHT results of Sgr A*. Thus, these three rotating regular spacetimes and Kerr black holes are indiscernible in some parameter space, and one cannot rule out the possibility of the former being strong candidates to be astrophysical black holes.
Journal Article
Photon Shells, Black Hole Shadows, and Accretion Toroids
We analyze the properties of the Kerr black hole (BH) photon shell, focusing on the influence of aggregates of corotating and counterrotating toroids (ringed accretion disks, hereafter RAD), orbiting in the BH photon shell (photon shell “obscuration”). The particular case of a corotating accretion disk orbiting in the BH ergoregion is also investigated. We study influence on the BH shadow boundary, fixing the conditions under which it is possible to observe the ergoregion and RAD “imprint” on the shadows boundary. In general, remarkable differences appear between the counterrotating photon components of the boundary with respect to the corotating ones. Various regions of the shadow boundary generated from orbital regions linked to the aggregates of orbiting structures have been analyzed. In particular, we investigate the bound unstable spherical photon orbits in the ergoregion, or at the inversion point, where (toroidal) ϕ̇=0 , or with the impact parameter ℓ = 0 to characterize the effects of the frame dragging on the boundary. Five main classes of BHs have been identified by distinguishable features of their photon shells (and shadow boundaries) in the context of the orbiting RAD.
Journal Article
The hole story
When Hamish and Hermione Hole are chased out of the cheese where they live, they search for a new home wreaking havoc wherever they go, but their luck turns when they are discovered resting in a piece of wood by a palace carpenter, who knows that holes can be really useful, especially when making two beautiful flutes.
Book
Bumblebee Black Holes in Light of Event Horizon Telescope Observations
We report the existence of novel static spherical black hole solutions in a vector–tensor gravitational theory called the bumblebee gravity model, which extends the Einstein–Maxwell theory by allowing the vector to nonminimally couple to the Ricci curvature tensor. A test of the solutions in the strong-field regime is performed for the first time using the recent observations of the supermassive black hole shadows in the galaxy M87 and the Milky Way from the Event Horizon Telescope Collaboration. The parameter space is found largely unexcluded and more experiments are needed to fully bind the theory.
Journal Article