The discovery
Astronomers have found a star that passes closer to the Milky Way's central black hole than any known star. The star is called S301. It orbits Sagittarius A*, the supermassive black hole at the center of our galaxy. The discovery was made using the GRAVITY instrument at the Very Large Telescope Interferometer in Chile.
The team tracked several stars orbiting the black hole over many years. One of them, S301, came remarkably close during its orbit. Its path bends sharply as the black hole's gravity pulls on it. The motion matches predictions from Einstein's theory of general relativity.
Why it matters
Stars that pass close to a black hole act as natural probes. Their motion reveals the strength of the gravitational field. Scientists can use these measurements to test physics under extreme conditions. S301 gives researchers a new tool for this work.
The star could help measure the spin of Sagittarius A*. A black hole's spin affects how space curves around it. Measuring spin has been a long-standing goal in astronomy. S301's close approach makes that measurement possible.
What the spin would reveal
Knowing the spin would tell scientists how the black hole grew. A fast spin suggests the black hole accumulated matter steadily. A slow spin could mean it grew through mergers. The answer would shed light on the history of our galaxy.
The team plans to keep watching S301. Each orbit gives more data. The next close approach could provide the needed measurements. Astronomers say the results may come within a few years.