Compact objects in bimetric general relativity

This chapter introduces the different classes of compact objects—white dwarfs, neutron stars, and black holes—that are relevant for gravitational-wave astronomy. The ideas are placed in the context of developing an understanding of the likely endpoint(s) of stellar evolution. Key ideas like Fermi gases and the Chandrasekhar mass are discussed, as is the emergence of general relativity as a cornerstone of astrophysics in the 1950s. Issues associated with different formation channels for, in particular, black holes are considered. The chapter ends with a discussion of the supermassive black holes that are found at the centre of galaxies.

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Compact Objects in General Relativity and Beyond

Modified Gravity and Cosmology ◽

10.1007/978-3-030-83715-0_23 ◽

2021 ◽

pp. 329-355

Author(s):

Jose Luis Blázquez-Salcedo ◽

Burkhard Kleihaus ◽

Jutta Kunz

Keyword(s):

General Relativity ◽

Compact Objects

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Asymptotically flat vacuum solution in modified theory of Einstein’s gravity

The European Physical Journal C ◽

10.1140/epjc/s10052-019-7396-x ◽

2019 ◽

Vol 79 (10) ◽

Author(s):

Surajit Kalita ◽

Banibrata Mukhopadhyay

Keyword(s):

General Relativity ◽

Vacuum Solution ◽

Compact Objects ◽

Schwarzschild Solution ◽

Asymptotically Flat ◽

Symmetric Vacuum ◽

Theory Of Gravity ◽

Bound Orbits ◽

Vacuum Spacetime ◽

The Universe

Abstract A number of recent observations have suggested that the Einstein’s theory of general relativity may not be the ultimate theory of gravity. The f(R) gravity model with R being the scalar curvature turns out to be one of the best bet to surpass the general relativity which explains a number of phenomena where Einstein’s theory of gravity fails. In the f(R) gravity, behaviour of the spacetime is modified as compared to that of given by the Einstein’s theory of general relativity. This theory has already been explored for understanding various compact objects such as neutron stars, white dwarfs etc. and also describing evolution of the universe. Although researchers have already found the vacuum spacetime solutions for the f(R) gravity, yet there is a caveat that the metric does have some diverging terms and hence these solutions are not asymptotically flat. We show that it is possible to have asymptotically flat spherically symmetric vacuum solution for the f(R) gravity, which is different from the Schwarzschild solution. We use this solution for explaining various bound orbits around the black hole and eventually, as an immediate application, in the spherical accretion flow around it.

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Gravitational field of compact objects in general relativity

Physical Review D ◽

10.1103/physrevd.86.064043 ◽

2012 ◽

Vol 86 (6) ◽

Cited By ~ 27

Author(s):

Kuantay Boshkayev ◽

Hernando Quevedo ◽

Remo Ruffini

Keyword(s):

General Relativity ◽

Gravitational Field ◽

Compact Objects

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Beyond Einstein’s General Relativity: Hybrid metric-Palatini gravity and curvature-matter couplings

International Journal of Modern Physics D ◽

10.1142/s0218271820300086 ◽

2020 ◽

Vol 29 (13) ◽

pp. 2030008 ◽

Cited By ~ 2

Author(s):

Tiberiu Harko ◽

Francisco S. N. Lobo

Keyword(s):

General Relativity ◽

Human Mind ◽

Compact Objects ◽

Cosmic Acceleration ◽

Modified Theories Of Gravity ◽

Late Time ◽

Gravitational Fields ◽

Matter Coupling ◽

Theories Of Gravity ◽

Einstein’S General Relativity

Einstein’s General Relativity (GR) is possibly one of the greatest intellectual achievements ever conceived by the human mind. In fact, over the last century, GR has proven to be an extremely successful theory, with a well established experimental footing, at least for weak gravitational fields. Its predictions range from the existence of black holes and gravitational radiation (now confirmed) to the cosmological models. Indeed, a central theme in modern Cosmology is the perplexing fact that the Universe is undergoing an accelerating expansion, which represents a new imbalance in the governing gravitational equations. The cause of the late-time cosmic acceleration remains an open and tantalizing question, and has forced theorists and experimentalists to question whether GR is the correct relativistic theory of gravitation. This has spurred much research in modified theories of gravity, where extensions of the Hilbert–Einstein action describe the gravitational field, in particular, [Formula: see text] gravity, where [Formula: see text] is the curvature scalar. In this review, we perform a detailed theoretical and phenomenological analysis of specific modified theories of gravity and investigate their astrophysical and cosmological applications. We present essentially two largely explored extensions of [Formula: see text] gravity, namely: (i) the hybrid metric-Palatini theory; (ii) and modified gravity with curvature-matter couplings. Relative to the former, it has been established that both metric and Palatini versions of [Formula: see text] gravity possess interesting features but also manifest severe drawbacks. A hybrid combination, containing elements from both of these formalisms, turns out to be very successful in accounting for the observed phenomenology and avoids some drawbacks of the original approaches. Relative to the curvature-matter coupling theories, these offer interesting extensions of [Formula: see text] gravity, where the explicit nonminimal couplings between an arbitrary function of the scalar curvature [Formula: see text] and the Lagrangian density of matter, induces a nonvanishing covariant derivative of the energy-momentum tensor, which implies nongeodesic motion and consequently leads to the appearance of an extra force. We extensively explore both theories in a plethora of applications, namely, the weak-field limit, galactic and extragalactic dynamics, cosmology, stellar-type compact objects, irreversible matter creation processes and the quantum cosmology of a specific curvature-matter coupling theory.

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Gravitational wave astronomy, relativity tests, and massive black holes

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309990469 ◽

2009 ◽

Vol 5 (S261) ◽

pp. 240-248 ◽

Cited By ~ 2

Author(s):

Peter L. Bender

Keyword(s):

General Relativity ◽

Gravitational Wave ◽

Galactic Center ◽

Galactic Nuclei ◽

Compact Objects ◽

Mass Ratio ◽

Intermediate Mass ◽

Massive Black Holes ◽

New Information ◽

Laser Interferometer Space Antenna

AbstractThe gravitational wave detectors that are operating now are looking for several kinds of gravitational wave signals at frequencies of tens of Hertz to kilohertz. One of these is mergers of roughly 10 M⊙ BH binaries. Sometime between now and about 8 years from now, it is likely that signals of this kind will be observed. The result will be strong tests of the dynamical predictions of general relativity in the high field regime. However, observations at frequencies below 1 Hz will have to wait until the launch of the Laser Interferometer Space Antenna (LISA), hopefully only a few years later. LISA will have 3 main objectives, all involving massive BHs. The first is observations of mergers of pairs of intermediate mass (100 to 105M⊙) and higher mass BHs at redshifts out to roughly z=10. This will provide new information on the initial formation and growth of BHs such as those found in most galaxies, and the relation between BH growth and the evolution of galactic structure. The second objective is observations of roughly 10 M⊙ BHs, neutron stars, and white dwarfs spiraling into much more massive BHs in galactic nuclei. Such events will provide detailed information on the populations of such compact objects in the regions around galactic centers. And the third objective is the use of the first two types of observations for testing general relativity even more strongly than ground based detectors will. As an example, an extreme mass ratio event such as a 10 M⊙ BH spiraling into a galactic center BH can give roughly 105 observable cycles during about the last year before merger, with a mean relative velocity of 1/3 to 1/2 the speed of light, and the frequencies of periapsis precession and Lense-Thirring precession will be high. The LISA Pathfinder mission to prepare for LISA is scheduled for launch in 2011.

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