This image plots the orbital paths of all known stars orbiting the enormous black hole at the center of the Milky Way. One of the stars, S301, comes very close to the black hole. At its closest point, the star travels at more than 15,000 miles per second. Max Planck Institute for Extraterrestrial Physics hide legend toggle title Max Planck Institute for Extraterrestrial Physics In the fall of 2002, scientists calculated the mass of a truly gigantic entity at the heart of our galaxy, the Milky Way. It was four million times the mass of our Sun, so large that it almost certainly had to be a supermassive black hole. The object “probably looks like Interstellar,” says Stefan Gillessen, an astronomer at the Max Planck Institute for Extraterrestrial Physics in Germany, referring to the 2014 science fiction film starring Matthew McConaughey and Anne Hathaway. “You have this dark shadow, this silhouette, where absolute darkness is” surrounded by a halo of bright light. There’s a reason some of our favorite images of black holes come from fiction: They’re actually very difficult to see. Black holes are, by their very nature, enormous enigmas (their gravitational pull is so powerful that not even light can escape), so learning something about them is like rescuing information from an abyss. But astronomers may have found an assistant luminary to help them solve that challenge. In new research published in the journal Nature on Wednesday, Gillessen and his colleagues describe the fastest star ever observed, racing around Sagittarius A*, the black hole at the heart of the Milky Way. Gillessen says that what is important about the discovery is not the speed of the star, but its proximity to the black hole. “This way we can use the star [as a probe] “We want to understand how black holes work and how they influence their direct environment,” says Gillessen, including the critical role they play in helping shape their galaxies. “And if you want to know more about black holes,” he adds, “the center of the Milky Way is the best laboratory we have.” It’s right on our doorstep.” Gillessen and his team used four of the European Southern Observatory’s telescopes in Chile at the Very Large Telescope site to collect infrared light, allowing them to see through cosmic dust and gas that might otherwise obscure their vision. “Just by using infrared light, you can look into the most central part of the Milky Way’s core,” says Felix Mang, a doctoral student at the Max Planck Institute for Extraterrestrials Physics The first time he noticed something curious in the data was a few years ago: “We were struck by a small flash of light, a very faint star moving at a very high speed,” he recalls. The stellar speed demon Mang followed the position of the star called S301 for the next two years and also looked back to determine where the star’s 8.7-year orbit took the shape of a super-elongated ellipse. of that oval. “The star moves forward in one direction, becoming faster and faster and then rotates very sharply around the black hole,” says Gillessen. This makes S301 the fastest star ever observed in the galaxy, after rotating around the supermassive black hole, “it flies away again and decelerates until it reaches its farthest point,” says Gillessen. “Once the orbit is known, it looks a lot like the Swiss railway system. Things are there exactly on time.” This discovery can teach researchers “about the gravitational potential of the black hole,” he says. “The star feels how space and time are distorted by the black hole. And so we can use the star to visualize how gravity acts in space and time.” Shedding light “This is a really exciting result,” says Erin Kara, an astrophysicist at MIT who was not involved in the study. “It kind of sets the stage in the next decade for making these kinds of unprecedented measurements of black holes.” This includes determining how fast the black hole at the center of our galaxy spins, a behavior that can drag surrounding space-time with it. “What I love about black holes,” Kara says, “is that both are exotic and where our understanding of physics breaks down. And at the same time, they’re really instrumental in explaining why our galaxy looks the way it does.” The notion of a star buzzing around a black hole tickles Gillessen’s imagination. “You’re always working at the edge of the possible,” he says. Consider what it would be like to be an alien living on a hypothetical planet orbiting S301. “Every nine years, you might see this black hole popping up big in the sky,” he says. “I mean, it must be absolutely stunning to have that kind of thing. experience.” It evokes the view, looking toward a pitch-black disk enveloped in light: a portal into the very fabric of the universe.
