100,000 times faster than a passenger plane: The fastest star in the Milky Way
Astronomers have discovered S301, a star orbiting the black hole at the center of the Milky Way at a speed reaching about 25,000 km/s. Researchers hope that with its help, they will be able to test Einstein's theory and measure the rotation of the black hole.
Astronomers have discovered what is considered the fastest star ever observed in the Milky Way — it moves at a speed that is almost impossible to imagine: about 25,000 kilometers per second. The star, named S301, orbits the supermassive black hole at the center of our galaxy, Sagittarius A*, in an extremely tight and fast orbit. The results of the discovery were published in the journal Nature, and researchers hope that the new star will become an especially important tool in the coming years for studying the black hole and testing some of the predictions of Einstein's theory of relativity.
According to Reinhard Genzel, director of the Max Planck Institute for Extraterrestrial Physics and winner of the 2020 Nobel Prize in Physics, long years of precise tracking of the stars orbiting Sagittarius A* are what made the discovery possible. According to him, the extreme proximity of S301 to the black hole "opens a new window" for studying the fundamental characteristics of space and time in a region where gravity is immense.
One of the things that makes S301 exceptional is its orbit. The star completes a full orbit around the black hole in just 8.7 years — a very short time in astronomical terms. At the closest point in its orbit, it reaches a distance equal to about 12 times the distance between the Earth and the Sun. It is precisely there that it accelerates to its maximum speed: about 25,000 kilometers per second.
"For comparison, this is a speed about 100,000 times higher than that of a passenger plane, and about 8% of the speed of light. In doing so, it surpasses all other stars currently known in the galaxy in terms of speed."
The star was discovered using the Very Large Telescope (VLT) array of the European Southern Observatory in Chile, and using the GRAVITY+ instrument, which allows scientists to perform highly accurate measurements of objects in the vicinity of the galactic center.
For the researchers, the impressive speed is only part of the story. Because of S301's extreme orbit and its proximity to the black hole, it may allow scientists to more directly measure the rotation rate of Sagittarius A*. The expectation is that within about ten years, it will be possible to use observations of it to test how well the behavior of space and time in the vicinity of the black hole matches Einstein's predictions. In other words, the fastest star in the Milky Way may also become one of the most intriguing natural laboratories of modern astronomy.
