Magnetars are the bizarre super-dense remnants of supernova explosions. They are the strongest magnets known in the universe — millions of times more powerful than the strongest magnets on Earth. Astronomers now believe they’ve found the partner star of a magnetar for the first time. This discovery helps to explain how magnetars form — a conundrum dating back 35 years — and why this particular star didn’t collapse into a black hole as astronomers would expect.