Related papers: Ghost stars in general relativity
Recently modified gravitational theories which mimic the behaviour of dark matter, the so-called "Mimetic Dark Matter", have been proposed. We study the consistency of such theories with respect to the absence of ghost instability and…
Dark energy is the component in the present Universe with the greatest abundance, and it is responsible for the accelerating expansion of the Universe. As a result, dark energy is likely to interact with any compact astrophysical object…
We develop a theoretical framework to study slowly rotating compact stars in a rather general class of alternative theories of gravity, with the ultimate goal of investigating constraints on alternative theories from electromagnetic and…
Both the static and homogeneous metrics describing the spherically symmetric gravitational field of a crossflow of incoming and outgoing null dust streams are generalized for the case of the two-component ghost radiation. Static solutions…
A new, Eddington inspired theory of gravity was recently proposed by Banados and Ferreira. It is equivalent to General Relativity in vacuum, but differs from it inside matter. This viable, one parameter theory was shown to avoid…
A static, spherically symmetric spacetime with negative pressures is conjectured inside a star. The gravitational field is repulsive and so a central singularity is avoided. The positive energy density and the pressures of the imperfect…
Strange stars with low masses are suggested to exist in reality, the origin of which could be via accretion-induced collapse (AIC) of white dwarfs. Such a strange star is likely bare, and would thus spin very fast, even to a period of < 0.1…
Motivated by the recent "Cosmos Project" observation of dark-matter concentrations with no ordinary matter in the same place, we study the question of the existence of compact objects made of pure dark matter. We assume that the dark matter…
A general relativistic solution, composed of a Zel'dovich-Letelier interior made of radial strings matched through a spherical thin shell at radius $r_0$ to an exterior Schwarzschild solution with mass $m$, is presented. It is the…
The properties of exotic stars are investigated. In particular, we study objects made entirely of dark matter and we take into account intrinsic anisotropies which have been ignored so far. We obtain exact analytical solutions to the…
The existence of extremely dark and compact astronomical bodies is by now a well established observational fact. On the other hand, classical General Relativity predicts the existence of black holes which fit very well with the…
We investigate the gravitational collapse of a spherically symmetric, inhomogeneous star, which is described by a perfect fluid with heat flow and satisfies the equation of state $p=\rho/3$ or $p=C\rho^\ga$ at its center. Different from the…
The interest in studying relativistic compact objects play an important role in modern astrophysics with an aim to understand several astrophysical issues. It is therefore natural to ask for internal structure and physical properties of…
Neutron stars are highly compact astrophysical objects and therefore of utmost relevance to learn about theories of gravity. Whereas the proper equation of state of the nuclear matter inside neutron stars is not yet known, and a wide range…
We study the first cosmological implications of the mimetic theory of massive gravity recently proposed by Chamseddine and Mukhanov. This is a novel theory of ghost-free massive gravity which additionally contains a mimetic dark matter…
In this lecture, we give a first introduction to neutron stars, based on fundamental physical principles. After outlining their outstanding macroscopic properties, as obtained from observations, we infer the extreme conditions of matter in…
A new final state of gravitational collapse is proposed. By extending the concept of Bose-Einstein condensation to gravitational systems, a cold, dark, compact object with an interior de Sitter condensate $p_{_V} = -\rho_{_V}$ and an…
Oppenheimer and Snyder found in 1939 that gravitational collapse in vacuum produces a "frozen star", i.e., the collapsing matter only asymptotically approaches the gravitational radius (event horizon) of the mass, but never crosses it…
We argue that there may exist spacetime defects embedded in Minkowski spacetime, which have negative active gravitational mass. One such spacetime defect then repels a test particle, corresponding to what may be called "antigravity."
The cosmological constant problem represents an evident tension between our present description of gravity and particle physics. Many solutions have been proposed, but experimental tests are always difficult or impossible to perform and…