Astronomers find fastest star S301 orbiting Milky Way black hole at 25,000 km/s

Stellar speed record at the galactic core

Astronomers have detected S301, the fastest known star in the Milky Way, orbiting the supermassive black hole Sagittarius A* at the centre of the galaxy. The star reaches velocities of 25,000 kilometres per second (approximately 56 million miles per hour or 15,534 miles per second), which represents more than 8% of the speed of light. This velocity is roughly 100,000 times faster than a commercial airliner. Sagittarius A* is situated 26,000 light-years from Earth and contains a mass equal to roughly 4 million to 4.3 million solar masses. The research, led by astrophysicists at the Max Planck Institute for Extraterrestrial Physics, appeared in the journal Nature on 19 August 2026.

That star is really, extremely fast.

Orbital mechanics and binary star origin

S301 is about 50% more massive and five times brighter than the Sun. The star travels in an eccentric orbit with a period of 8.7 years, bringing it ten times closer to the black hole than any previously tracked celestial body. At pericentre, its closest approach, S301 passes within 11.5 to 12 astronomical units of Sagittarius A*, a distance comparable to the gap between the Sun and Saturn. At its apocentre, the star recedes to approximately 1,360 astronomical units. Astrophysicists deduce that S301 originally belonged to a binary pair. Gravitational interaction with Sagittarius A* separated the system, ejecting one partner star out of the Milky Way while capturing S301 in an enduring orbit.

What is special about this star is that it's orbiting Sagittarius A* on a very tight orbit, taking just 8.7 years to complete it, and is approaching the black hole at a mere 12 times the distance of Earth to the Sun. That is unprecedented.

Measuring black hole spin and spacetime warping

Because black holes emit no light, researchers rely on nearby stars as natural probes to examine the surrounding environment. According to general relativity and the no-hair theorem, an isolated black hole is characterised by its mass, charge, and angular momentum. While the mass of Sagittarius A* (nearly 10^37 kilograms) has been calculated using roughly 40 to 50 mapped stellar trajectories, its spin has never been directly measured. A spinning black hole drags local spacetime along with its rotation, altering the precession of nearby orbits. Astronomers aim to determine the rotation rate of Sagittarius A* within the next decade by monitoring perturbations in S301's flight path.

For the first time, we would actually be able to measure very directly the spin of a massive black hole, which would be a key test of Einstein's theory.

Observations with the Very Large Telescope

The detection relied on the European Southern Observatory's Very Large Telescope Interferometer, located in the Atacama Desert in Chile. The system combines infrared signals from four individual eight-metre telescopes to resolve faint targets through dense interstellar dust. Researchers first noticed the faint light of S301 in spring 2023, subsequently assembling 19 precise positional measurements from data extending back to 2017. Those records revealed that the star made its closest pass by the black hole in early 2023. Astronomers expect additional high-velocity stars to emerge as infrared observation instruments become more sensitive.