A STAR near the centre of the Milky Way is hurtling through its orbit with a peak speed of more than 8 per cent the speed of light, making it both the fastest star and the closest one to a supermassive black hole that has ever been spotted. Named S301, this astonishing star could help us unravel the secrets of gravity. Measuring Earth’s spin is relatively easy, but a black hole’s spin is much harder to determine because of its lack of a visible surface. The most precise way to measure it would be by measuring frame dragging, and S301 is the first star close enough to feel that effect. …