Abstract:
We study formation of black holes in the Friedmann universe. We present a formulation of the Einstein equations under the constant mean curvature time-slicing condition. Our formalism not only gives us the analytic solution of the perturbation equations for non-linear density and metric fluctuations on superhorizon scales, but also allows us to carry out a numerical relativity simulation for black hole formation after the scale of the density fluctuations is well within the Hubble horizon scale. We perform a numerical simulation of spherically symmetric black hole formation in the radiation-dominated, spatially flat background universe for a realistic initial condition supplied from the analytic solution. It is found that the initial metric perturbation has to be non-linear (the maximum value of 3D conformal factor $\psi_0$ at $t=0$ should be larger than $\sim 1.4$) for a black hole to be formed, but the threshold amplitude for black hole formation and the final black hole mass considerably depend on the initial density (or metric) profile of the perturbation: The threshold value of $\psi_0$ at $t=0$ for formation of a black hole is smaller for a high density peak surrounded by a low density region than for that surrounded by the average density region of the flat universe. This suggests that it is necessary to take into account the spatial correlation of density fluctuations in the study of primordial black hole formation.

Abstract:
Throughout its journey universe follows strong gravity. By unifying general theory of relativity and quantum mechanics a simple derivation is given for rotating black hole's temperature. It is shown that when the rotation speed approaches light speed temperature approaches Hawking's black hole temperature. Applying this idea to the cosmic black hole it is noticed that there is "no cosmic temperature" if there is "no cosmic rotation". Starting from the Planck scale it is assumed that universe is a rotating and expanding black hole. Another key assumption is that at any time cosmic black hole rotates with light speed. For this cosmic sphere as a whole while in light speed rotation "rate of decrease" in temperature or "rate of increase" in cosmic red shift is a measure of "rate of cosmic expansion". Since 1992, measured CMBR data indicates that, present CMB is same in all directions equal to $2.726^circ$ K, smooth to 1 part in 100,000 and there is no continuous decrease! This directly indicates that, at present rate of decrease in temperature is practically zero and rate of expansion is practically zero. Universe is isotropic and hence static and is rotating as a rigid sphere with light speed. At present galaxies are revolving with speeds proportional to their distances from the cosmic axis of rotation. If present CMBR temperature is $2.726^circ$ K, present value of obtained angular velocity is $2.17 imes 10^{-18}$ rad/sec $cong$ 67 Km/sec$ imes$Mpc. Present cosmic mass density and cosmic time are fitted with a $ln (volume ratio)$ parameter. Finally it can be suggested that dark matter and dark energy are ad-hoc and misleading concepts.

Abstract:
A new alternative cosmological model called black hole universe was recently developed by the author on the basis of the following three fundamentals: 1) the principle of spacetime black hole equivalence, 2) the cosmological principle of spacetime isotropy and homogeneity, and 3) the Einsteinian general theory of relativity that describes the effect of matter on spacetime. According to this black hole model of the universe, the author up-to-dately has self-consistently described the origin, structure, evolution, expansion, and acceleration of the universe, quantitatively explained the measurements of cosmic microwave background radiation, type Ia supernovae’s luminosity distance and redshift, and dynamic properties of star-like, massive, and supermassive black holes such as gamma-ray bursts, X-rays flares from galactic centers, and quasars, and fully overcome the difficulties of the conventional model of the universe such as the problems of horizon, flatness, monopole, inflation, dark matter, dark energy, and so on. In this paper, the author will examine and overview thoroughly this new cosmological model and completely describe its development from the three fundamentals and its creative explanations to the existing observations of the universe. From this comprehensive investigation of the new cosmological model, the author will further reveal the fundamental regularities and laws of the black hole universe with respect to the spacetime mass and radius, spacetime equilibrium, spacetime expansion and acceleration, spacetime radiation energy, and spacetime entropy variation. These efforts will help us to uncover various regularities and mysteries of the universe.

Abstract:
Nature abhors an infinity. The limits of general relativity are often signaled by infinities: infinite curvature as in the center of a black hole, the infinite energy of the singular big bang. We might be inclined to add an infinite universe to the list of intolerable infinities. Theories that move beyond general relativity naturally treat space as finite. In this review we discuss the mathematics of finite spaces and our aspirations to observe the finite extent of the universe in the cosmic background radiation.

Abstract:
Gravitational waves (GWs) are fluctuations in the fabric of spacetime predicted by Einstein's theory of general relativity. Using a collection of millisecond pulsars as high-precision clocks, the nanohertz band of this radiation is likely to be directly detected within the next decade. Nanohertz-frequency GWs are expected to be emitted by mergers of massive black hole binary systems, and potentially also by cosmic strings or superstrings formed in the early Universe. Direct detection of GWs will open a new window to the Universe, and provide astrophysical information inaccessible via electromagnetic observations. In this paper, we describe the potential sources of low-frequency GWs and the current status and key advances needed for the detection and exploitation of GWs through pulsar timing.

Abstract:
Black holes are popping up all over the place: in compact binary X-ray sources and GRBs, in quasars, AGNs and the cores of all bulge galaxies, in binary black holes and binary black hole-neutron stars, and maybe even in the LHC! Black holes are strong-field objects governed by Einstein's equations of general relativity. Hence general relativistic, numerical simulations of dynamical phenomena involving black holes may help reveal ways in which black holes can form, grow and be detected in the universe. To convey the state-of-the art, we summarize several representative simulations here, including the collapse of a hypermassive neutron star to a black hole following the merger of a binary neutron star, the magnetorotational collapse of a massive star to a black hole, and the formation and growth of supermassive black hole seeds by relativistic MHD accretion in the early universe.

Abstract:
Formation and energy emission of quasars are investigated in accord with the black hole universe, a new cosmological model recently developed by Zhang. According to this new cosmological model, the universe originated from a star-like black hole and grew through a supermassive black hole to the present universe by accreting ambient matter and merging with other black holes. The origin, structure, evolution, expansion, and cosmic microwave background radiation of the black hole universe have been fully explained in Paper I and II. This study as Paper III explains how a quasar forms, ignites and releases energy as an amount of that emitted by dozens of galaxies. A main sequence star, after its fuel supply runs out, will, in terms of its mass, form a dwarf, a neutron star, or a black hole. A normal galaxy, after its most stars have run out of their fuels and formed dwarfs, neutron stars, and black holes, will eventually shrink its size and collapse towards the center by gravity to form a supermassive black hole with billions of solar masses. This collapse leads to that extremely hot stellar black holes merge each other and further into the massive black hole at the center and meantime release a huge amount of radiation energy that can be as great as that of a quasar. Therefore, when the stellar black holes of a galaxy collapse and merge into a supermassive black hole, the galaxy is activated and a quasar is born. In the black hole universe, the observed distant quasars powered by supermassive black holes can be understood as donuts from the mother universe. They were actually formed in the mother universe and then swallowed into our universe. The nearby galaxies are still very young and thus quiet at the present time. They will be activated and further evolve into quasars after billions of years. At that time, they will enter the universe formed by the currently observed distant quasars as similar to the distant quasars entered our universe. The entire space evolves iteratively. When one universe expands out, a new similar universe is formed from its inside star-like or supermassive black holes.

Abstract:
A new cosmological model called black hole universe is proposed. According to this model, the universe originated from a hot star-like black hole with several solar masses, and gradually grew up through a supermassive black hole with billion solar masses to the present state with hundred billion-trillion solar masses by accreting ambient materials and merging with other black holes. The entire space is structured with infinite layers hierarchically. The innermost three layers are the universe that we are living, the outside called mother universe, and the inside star-like and supermassive black holes called child universes. The outermost layer is infinite in radius and limits to zero for both the mass density and absolute temperature. The relationships among all layers or universes can be connected by the universe family tree. Mathematically, the entire space can be represented as a set of all universes. A black hole universe is a subset of the entire space or a subspace. The child universes are null sets or empty spaces. All layers or universes are governed by the same physics - the Einstein general theory of relativity with the Robertson-walker metric of spacetime - and tend to expand outward physically. The evolution of the space structure is iterative. When one universe expands out, a new similar universe grows up from its inside. The entire life of a universe begins from the birth as a hot star-like or supermassive black hole, passes through the growth and cools down, and expands to the death with infinite large and zero mass density and absolute temperature. The black hole universe model is consistent with the Mach principle, the observations of the universe, and the Einstein general theory of relativity. Its various aspects can be understood with the well-developed physics without any difficulty. The dark energy is not required for the universe to accelerate its expansion. The inflation is not necessary because the black hole universe does not exist the horizon problem.

Abstract:
Based on the big bang concepts- in the expanding universe, ‘rate of decrease in CMBR temperature’ is a measure of the cosmic ‘rate of expansion’. Modern standard cosmology is based on two contradictory statements. They are - present CMBR temperature is isotropic and the present universe is accelerating. In particle physics also, till today there is no practical evidence for the existence of ‘dark matter’ and ‘dark energy’. Astronomers are puzzled by the announcement that the masses of the largest objects in the Universe appear to depend on which method is used to weigh them. Recent observations and discussions at Astrophysics Research Institute (ARI) supported by the Royal Astronomical Society create new thoughts on the existence of the ‘cosmic axis of evil’. In this connection an attempt is made to study the universe with a closed and growing model of cosmology. If the primordial universe is a natural setting for the creation of black holes and other non-perturbative gravitational entities, it is also possible to assume that throughout its journey, the whole universe is a primordial (growing and rotating) cosmic black hole. Planck particle can be considered as the baby universe.

Abstract:
The discovery of cosmic acceleration has presented a unique challenge for cosmologists. As observational cosmology forges ahead, theorists have struggled to make sense of a standard model that requires extreme fine tuning. This challenge is known as the cosmological constant problem. The theory of gravitational aether is an alternative to general relativity that does not suffer from this fine-tuning problem, as it decouples the quantum field theory vacuum from geometry, while remaining consistent with other tests of gravity. In this paper, we study static black hole solutions in this theory and show that it manifests a UV-IR coupling: Aether couples the spacetime metric close to the black hole horizon, to metric at infinity. We then show that using the Trans-Planckian ansatz (as a quantum gravity effect) close to the black hole horizon, leads to an accelerating cosmological solution, far from the horizon. Interestingly, this acceleration matches current observations for stellar mass black holes. Based on our current understanding of the black hole accretion history in the Universe, we then make a prediction for how the effective dark energy density should evolve with redshift, which can be tested with future dark energy probes.