GP-B Post-Flight Analysis—Final Report - Gravity Probe B - Stanford ...

Figure 2-9. Frame-dragging around a black holeAt the GP-B press conference held at NASA Headquarters in April 2004, just prior to the GP-B launch, Caltechphysicist Kip Thorne, one of the world’s leading experts on black holes, made the following comments on thesignificance of the frame-dragging effect:“The black dot in the center [of Figure 2-9 above] represents a black hole. It is surrounded by anaccretion disc of gas, shown in yellow, that we believe is forced into the equatorial plane of the blackhole by the dragging of spacetime in that vicinity. Jets of energy [blue light in the figure] shoot out inboth directions along the spin axis produced by frame-dragging around the black hole. Furthermore,the interaction of the frame-dragging around black holes with magnetic fields is responsible for theenormous and destructive power generation that produces the jets of energy streaming out of theseobjects.”Thorne then concluded:“The results of the GP-B experiment will enable us to verify that the frame-dragging effect doesindeed exist, and that it is directly proportional to the angular momentum of our spinning Earth.Physicists and cosmologists will then be able to extrapolate these frame-dragging measurementsaround the Earth to much more massive celestial objects, such as black holes and quasars.”2.1.6 The Basic GP-B Experimental DesignConceptually, the GP-B experiment is simple: Place a gyroscope and a telescope in a polar-orbiting satellite,about 642 km (400 mi) above the Earth. (GP-B actually uses four gyroscopes for redundancy.) At the start of theexperiment, align both the telescope and the spin axis of the gyroscope with a distant reference point—a guidestar. Keep the telescope aligned with the guide star for a year, as the spacecraft makes over 5,000 orbits aroundthe Earth, and measure the change in the spin axis alignment of the gyros over this period in both the plane ofthe orbit (the geodetic drift) and orthogonally in the plane of the Earth’s rotation (frame-dragging drift).Figure 2-10 below shows a conceptual diagram of the GP-B experimental design.Gravity Probe B — Post Flight Analysis • Final Report March 2007 35