Frame-dragging
Frame-dragging is an effect on spacetime, predicted by Albert Einstein's general theory of relativity, that is due to non-static stationary distributions of mass–energy.
More generally, the subject that deals with the effects caused by mass–energy currents is known as gravitoelectromagnetism, which is analogous to the magnetism of classical electromagnetism.
[1][2][3] They predicted that the rotation of a massive object would distort the spacetime metric, making the orbit of a nearby test particle precess.
Under the Lense–Thirring effect, the frame of reference in which a clock ticks the fastest is one which is revolving around the object as viewed by a distant observer.
For example, imagine that a north–south-oriented ice skater, in orbit over the equator of a rotating black hole and rotationally at rest with respect to the stars, extends her arms.
Curiously, any denizens inside the yoyo will not feel any torque and will not experience any felt change in angular momentum.
In 1976 Van Patten and Everitt[6][7] proposed to implement a dedicated mission aimed to measure the Lense–Thirring node precession of a pair of counter-orbiting spacecraft to be placed in terrestrial polar orbits with drag-free apparatus.
[14] Recently, a comprehensive overview of the attempts to measure the Lense-Thirring effect with artificial satellites was published in the literature.
[16][17][18] The Gravity Probe B experiment[19][20] was a satellite-based mission by a Stanford group and NASA, used to experimentally measure another gravitomagnetic effect, the Schiff precession of a gyroscope,[21][22][23] to an expected 1% accuracy or better.
[25] In 2008 the Senior Review Report of the NASA Astrophysics Division Operating Missions stated that it was unlikely that the Gravity Probe B team will be able to reduce the errors to the level necessary to produce a convincing test of currently untested aspects of General Relativity (including frame-dragging).
[26][27] On May 4, 2011, the Stanford-based analysis group and NASA announced the final report,[28] and in it the data from GP-B demonstrated the frame-dragging effect with an error of about 19 percent, and Einstein's predicted value was at the center of the confidence interval.
A research group in Italy,[33] USA, and UK also claimed success in verification of frame dragging with the Grace gravity model, published in a peer reviewed journal.
Gravitomagnetic forces produced by the Lense–Thirring effect (frame dragging) within the ergosphere of rotating black holes[36][37] combined with the energy extraction mechanism by Penrose[38] have been used to explain the observed properties of relativistic jets.
The gravitomagnetic model developed by Reva Kay Williams predicts the observed high energy particles (~GeV) emitted by quasars and active galactic nuclei; the extraction of X-rays, γ-rays, and relativistic e−– e+ pairs; the collimated jets about the polar axis; and the asymmetrical formation of jets (relative to the orbital plane).
It touches the inner surface at the poles of the rotation axis, where the colatitude θ equals 0 or π; its radius in Boyer-Lindquist coordinates is defined by the formula where the purely temporal component gtt of the metric changes sign from positive to negative.
However, this is impossible within the ergosphere, where gtt is negative, unless the particle is co-rotating with the interior mass M with an angular speed at least of Ω.
