An international team of astronomers has discovered the fastest known star in the Milky Way galaxy, moving at speeds of up to 25,000 kilometers per second, or more than 8% of the speed of light, as it orbits the supermassive black hole at the center of the galaxy.
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This discovery gives scientists an unprecedented opportunity to measure the rotation of the black hole itself, and to test Einstein's predictions about the impact of massive objects on space and time.
The results were published in the journal Nature on August 19, 2026, after researchers were able to observe the star using advanced equipment at the European Southern Observatory in Chile, and analyze previous observations to track its precise movement.
A faint star in the most crowded region of the galaxy
The black hole known as Sagittarius A* is located at the heart of the Milky Way. Its mass is about 4.3 million times that of the Sun, and stars orbit it, subject to its enormous gravity. However, observing them is not easy due to the crowding of the region and the difficulty of distinguishing faint objects.
The discovery of S-301 was a particular challenge, as it was about two billion times fainter than Betelgeuse, one of the brightest stars in the sky, and its detection was only made possible by using the GRAVITY instrument, which combines observations from huge telescopes to obtain extremely accurate measurements.
Researchers believe the star was part of a binary star system before it was torn apart by the gravity of the black hole, with one star being propelled away and the other remaining trapped in an extremely elongated orbit.
Does the star reveal the rotation of the black hole?
The great value of the discovery lies in the star's proximity to the black hole, as its intense gravity causes it to move within a region where the effect of the black hole's rotation can appear in the surrounding fabric of spacetime.
According to Einstein's theory of general relativity, a rotating black hole partially pulls the surrounding spacetime in the direction of its rotation, causing subtle changes in the orbits of nearby objects. Scientists can detect these changes by observing the star over the coming years.
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