How to glide in Schwarzschild spacetime

Veselý, Vítek; Žofka, Martin

doi:10.1088/1361-6382/ab0976

Cited by 7 publications

(4 citation statements)

References 18 publications

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“…Indeed, it can be difficult even to verify that certain models fall freely and do not violate energy conditions. Difficulties of this kind have led [8,9] to certain claims [10] for qualitatively non-Newtonian effects in general relativity, claims which were later refuted by a more general analysis related to the one considered here [11].…”

Section: Discussionmentioning

confidence: 99%

Extended-body effects and rocket-free orbital maneuvering

Harte,

Gaffney

2020

Preprint

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Celestial mechanics is most often concerned with the motion of pointlike, or at least sphericallysymmetric, masses. However, the orbits of more-complicated extended bodies can differ considerably from their point-particle counterparts. This is especially so if such a body-say a spacecraft-is able to actively modulate its shape. Except where forbidden by symmetries and their associated conservation laws, shape-changing spacecraft can in fact adjust their orbits arbitrarily (though slowly) without the use of reaction mass. We show that such maneuvers can be understood using elementary methods and without constructing any detailed model of a spacecraft's interior. In many cases, all of a spacecraft's design can be abstracted to the specification of a single time-dependent eigenvalue of its quadrupole moment. Appropriately varying this eigenvalue allows the energy and eccentricity of an orbit to be increased or decreased and its apses to be rotated arbitrarily. In other contexts, we show that extended-body effects can be used instead to stabilize unstable orbits.

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Section: Discussionmentioning

confidence: 99%

Extended-body effects and rocket-free orbital maneuvering

Harte,

Gaffney

2020

Preprint

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“…In this sense, KdS metric describes the geometry of spacetime when a single axially symmetric object is immersed in de Sitter background [22,23,24]. As a result, the photon sphere for KdS metric can be obtained by solving the following cubic equation…”

Section: Gm R 2 −mentioning

confidence: 99%

Black hole shadow to probe modified gravity

Stepanian,

Khlghatyan,

Gurzadyan

2021

Preprint

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We study the black hole's shadow for Schwarzschild-de Sitter and Kerr-de Sitter metrics with the contribution of the cosmological constant Λ. Based on the reported parameters of the M87* black hole shadow we obtain constraints for the Λ and show the agreement with the cosmological data. It is shown that, the coupling of the Λ-term with the spin parameter reveals peculiarities for the photon spheres and hence for the shadows. Within the parametrized post-Newtonian formalism the constraint for the corresponding Λ-determined parameter is obtained.

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“…In that case, there is one interesting question: Can a mass use extended-body effects to slow or accelerate its fall? This question has been addressed before [15,18,[21][22][23], using constrained Lagrangians which were purported to describe cyclicallydeforming spacecraft. Here, we show-without introducing interior models-that non-spinning, torque-free spacecraft can indeed control their falls.…”

Section: B Radial Infallmentioning

confidence: 99%

“…Following initial work by Wisdom [14], there has been a significant amount of literature already devoted to understanding rocket-free motion in general relativity [15][16][17][18][19][20][21][22][23]. The most striking claim which has sometimes been made is that relativistic extended bodies can "swim in spacetime" [14,17], a description chosen due to similarities with the swimming of microorganisms at low Reynolds numbers [24,25]: In certain limits, net translations were found to depend only on the sequence of shapes a spacecraft attains, and not on the speed of that sequence.…”

Section: Introductionmentioning

confidence: 99%

Extended-body motion in black hole spacetimes: What is possible?

Harte

2020

Preprint

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Free-fall is only approximately universal in general relativity: Different extended bodies can fall in different ways, depending on their internal dynamics. Nevertheless, certain aspects of free-fall are independent of those dynamics. This paper derives universal constraints on extended-body motion which hold in all vacuum type D spacetimes. Working in the quadrupole approximation, we show that in addition to the (previously-known) constraints imposed by Killing vectors, two components of the gravitational torque must vanish. Furthermore, of the ten components of a body's quadrupole moment, four are found to be irrelevant, two can affect only the force, and the remaining four can affect both forces and torques. As an application, we consider the capabilities of a hypothetical spacecraft which controls its motion by controlling its internal structure. In the Schwarzschild spacetime, such a spacecraft can control its mass, and by doing so, it can stabilize unstable orbits, escape from bound orbits, and more-all without a rocket.

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How to glide in Schwarzschild spacetime

Cited by 7 publications

References 18 publications

Extended-body effects and rocket-free orbital maneuvering

Extended-body effects and rocket-free orbital maneuvering

Black hole shadow to probe modified gravity

Extended-body motion in black hole spacetimes: What is possible?

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