Ergosphere

Ergospheres and horizons of a rotating black hole with the spin parameter a = 0.99.

Ergosphere refers to the outermost area of a rotating black hole drawn in violet in the sketch opposite and the innermost area of a rotating black hole drawn in red . From the outer limit, it is not possible for an object not to rotate; A prograde movement is thus imposed on the object . The reason for this phenomenon is the fact that a rotating mass "carries away" the space-time geometry, ie everything that is within the ergosphere is forced to rotate the black hole. In order for an object to be stationary relative to a distant observer, it would have to locally fly at faster than light speed against the direction of rotation of the central mass, which is physically impossible. However, up to the horizon it is still possible to escape into infinity with a radial impulse. From the outer limit of the inner ergosphere, it is again possible to move in any direction, as the frame dragging effect there is again below the speed of light. The size and behavior of the ergospheres are described by the Kerr metric .

A test particle that approaches the ergosphere in a retrograde direction is forced to change its direction of movement. Coordinate system: Boyer – Lindquist

The entrainment of spacetime geometry can be imagined visually like the deformation of a spider's web. When the object bending space-time is not moving, the spider web is wheel-shaped and the individual “spokes” of the wheel are running straight towards the object. But when the object rotates, it "twirls" the spider web in its center; H. the “spokes” are bent towards the center, and an image is created that resembles a whirlpool. Because of this continuous deformation , an object can no longer escape the rotation of the ergosphere , even if it were moving at the speed of light .

The spatial figure of the outer edge of the ergosphere is pumpkin-shaped, while its inner edge connects to the outer event horizon in the shape of a flattened ellipsoid of revolution. The extraction of rotational energy through the decay of a particle within the ergosphere is described by the Penrose process .

literature

Charles Misner , Kip S. Thorne , John A. Wheeler : Gravitation. WH Freeman, San Francisco 1973, ISBN 0-7167-0344-0 .
EF Taylor , JA Wheeler : Exploring black holes: Introduction to General Relativity , Addison-Wesley Longman, San Francisco 2000, ISBN 0-201-38423-X (Project F: The Spinning Black Hole).

Web links

Individual evidence

^ Matt Visser: The Kerr spacetime - a brief introduction. (First publication: arxiv : 0706.0622 ), page 35 , Fig. 3
^ Philip Russell Wallace : Physics: Imagination and Reality
^ Katherine Blundell: Black Holes: A Very Short Introduction p. 31

[1] Matt Visser: The Kerr spacetime - a brief introduction. (First publication: arxiv : 0706.0622 ), page 35 , Fig. 3

[2] Philip Russell Wallace : Physics: Imagination and Reality

[3] Katherine Blundell: Black Holes: A Very Short Introduction p. 31