IM Pegasi

Gravity Probe B gyroscope rotor and housing, 1995

The Gravity Probe B experiment was designed to test predictions of Einstein’s general theory of relativity: that a massive body such as the Earth should warp and twist the space-time around it. Four spheres like this one – among the most perfect ever made – were set spinning on a spacecraft precisely pointed towards a guide star. Scientists are currently analysing the mission data to see if the angle of the spheres’ spin was altered by the warp and twist.