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 to a supermassive black hole that has ever been spotted. Named S301, this astonishing star could help us unravel the secrets of gravity. Stefan Gillessen at the Max Planck Institute for Extraterrestrial Physics in Germany and his colleagues found S301 using the Very Large Telescope in Chile.
They have been watching it since 2023 to get enough data to pin down its orbit, and the results are unprecedented. Everything from cells to stars to particles exists on the edge of chaos At its closest approach, S301 is only about 1.8 billion kilometres from Sagittarius A*, the supermassive black hole at the centre of our galaxy. That’s just 12 times the distance between Earth and the sun, 10 times closer to Sagittarius A* than the previous record-holder.
Such a close pass by the black hole means that S301 spends part of its orbit in one of the most extreme gravitational environments in the universe. Next to a black hole, space-time stretches and warps. If a black hole is spinning, it should warp space-time even more, twisting it up in what is known as the frame-dragging effect.
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. If you can find a population of these stars, then you’re in business.” Gillessen and his team have several candidates for stars slightly further from the black hole than S301, but none yet that are closer, he says. But when we finally do measure the spin of a black hole, it will be a crucial piece of the cosmic jigsaw.
It will not only help us understand how black holes have contributed to the evolution of the universe, but will also provide a probe into the behaviour of gravity in extreme environments, which has proved extremely difficult to study. The mass was worth a Nobel prize in 2020, so, if you find the spin, you might expect a call from Stockholm in 20 years,” says Gillessen.
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